Medtronic W1DR01 Reference Guide

AZURE™ MRI SURESCAN™ / ASTRA™ MRI
SURESCAN™

MR Conditional implantable pacemakers with SureScan™ technology

Reference Manual
Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.

AZURE™ MRI SURESCAN™ / ASTRA™ MRI
SURESCAN™

Reference Manual

A reference manual for the Azure™ MRI SureScan™ and Astra™ MRI SureScan™ families of
implantable pacemakers

The following list includes trademarks or registered trademarks of Medtronic in the United
States and possibly in other countries. All other trademarks are the property of their respective
owners.

Astra, Azure, Capture Management, Cardiac Compass, CareAlert, CareLink,
CareLink Encore, Flashback, Marker Channel, Medtronic, Medtronic CareAlert,
Medtronic CareLink, MVP, Quick Look, Reactive ATP, SureScan, TherapyGuide

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Contents

1 Introduction .......................................................... 7

1.1 About the product literature ............................................ 7

1.2 Device features per model ............................................. 8

2 Patient follow-up guidelines .......................................... 11

2.1 In-clinic follow-up appointments and remote monitoring ................... 11

2.2 Optimizing device longevity ........................................... 16

3 Diagnostic data features ............................................. 19

3.1 Quick Look II summary data .......................................... 19

3.2 Medtronic CareAlert Monitoring ....................................... 21

3.3 Cardiac Compass Trends ............................................ 24

3.4 Arrhythmia Episodes data ............................................ 28

3.5 Episode and therapy counters ........................................ 32

3.6 Flashback Memory data ............................................. 34

3.7 Rate Drop Response Episodes ....................................... 35

3.8 MVP Mode Switches data ............................................ 35

3.9 Rate Histograms .................................................... 36

3.10 Device and lead performance data .................................... 37

3.11 Automatic device status monitoring .................................... 41

4 Pacing features ...................................................... 43

4.1 Sensing ........................................................... 43

4.2 Basic pacing ....................................................... 53

4.3 Implant Detection ................................................... 62

4.4 Lead Monitor ....................................................... 64

4.5 Managed Ventricular Pacing (MVP) .................................... 66

4.6 Rate Response ..................................................... 72

4.7 Capture Management ............................................... 77

4.8 Rate Adaptive AV ................................................... 87

4.9 Auto PVARP ....................................................... 89

4.10 Rate Drop Response ................................................ 91

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4.11 Rate Hysteresis ..................................................... 96

4.12 Sleep feature ....................................................... 97

4.13 Non-Competitive Atrial Pacing ........................................ 99

4.14 PMT Intervention .................................................. 100

4.15 PVC Response .................................................... 103

4.16 Ventricular Safety Pacing ............................................ 104

4.17 Mode Switch ...................................................... 106

4.18 Conducted AF Response ........................................... 109

4.19 Atrial Rate Stabilization ............................................. 111

4.20 Atrial Preference Pacing ............................................ 114

4.21 Post-Mode Switch Overdrive Pacing .................................. 118

4.22 Ventricular Rate Stabilization ........................................ 121

5 Tachyarrhythmia detection features .................................. 124

5.1 AT/AF detection ................................................... 124

5.2 VT Monitor ........................................................ 129

5.3 Suspending and resuming tachyarrhythmia detection ................... 132

6 Tachyarrhythmia therapy features ................................... 134

6.1 Atrial therapy scheduling ............................................ 134

6.2 Atrial ATP therapies ................................................ 139

Glossary ................................................................ 148

Index ................................................................... 154

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1 Introduction

1.1 About the product literature

This manual describes the operation and intended use of features offered by the Medtronic
Azure MRI SureScan and Astra MRI SureScan families of dual and single chamber MR
Conditional pacemakers.

Throughout this manual, the word “device” refers to the implanted pacemaker.

Unless otherwise noted, all device features described in this manual apply to Azure XT DR
MRI SureScan devices. To determine which features are available for another model in the
Azure MRI SureScan or Astra MRI SureScan family, refer to Section 1.2, “Device features per
model”, page 8. Any references in this manual to atrial or dual chamber operation apply
to dual chamber devices only. Single chamber devices provide ventricular operation only.

The report images, button labels, and navigation instructions in this manual apply to the
Medtronic Model SW030 software running on a Medtronic CareLink Model 2090
Programmer or a Medtronic CareLink Encore Model 29901 Programmer. The details of the
user interface are provided for reference only and may not match those of other applications.

The names of on-screen buttons are shown within brackets: [Button Name]. Navigation
paths to software screens or programmable parameters are shown with a “>” character
between each step in the path (for example, Params > Additional Features… > Rate
Hysteresis).

1.1.1 Product literature

Before implanting the device, it is recommended that you take the following actions:

●

Read the product literature for information about prescribing, implanting, and using the
device and conducting a patient follow-up session.

●

Thoroughly read the technical manuals for the leads used with the device. Also read the
technical manuals for other system components.

●

Discuss the device and implant procedure with the patient and any other interested
parties, and give them any patient information materials packaged with the device.

Additional information about the device is provided in the following documents:

MRI technical manual – This manual provides MRI-specific procedures and warnings and
precautions.

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Device manual – This manual contains model-specific feature information, indications and
contraindications, warnings and precautions, instructions for implanting the device, quick
reference specifications, and parameter tables.

Programming guide – This manual explains how to use the programmer software to
conduct a patient session.

Explanation of symbols – This document defines the symbols that may appear on the
device package. Refer to the package label to see which symbols apply specifically to this
device.

Radio regulatory compliance insert – This document provides compliance information
related to the radio components of the device.

Medical Procedure and EMI Warnings and Precautions Manual for Health Care
Professionals – This manual provides warnings, precautions, and guidance for health care

professionals who perform medical therapies and diagnostic procedures on cardiac device
patients. The manual also provides patient education information related to sources of
electromagnetic interference (EMI) at home, at work, and in other environments.

1.1.2 Technical support

Medtronic employs highly trained representatives and engineers located throughout the
world to serve you and, upon request, to provide training to qualified hospital personnel in the
use of Medtronic products.

In addition, Medtronic maintains a professional staff of consultants to provide technical
consultation to product users.

For more information, contact your local Medtronic representative, or call or write Medtronic
at the appropriate telephone number or address listed on the back cover.

1.2 Device features per model

The following table describes the availability of features within the Astra MRI SureScan and
Azure MRI SureScan device families. Feature availability for each device model is marked
with an X in the corresponding column.

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Notes:

●

Azure MRI SureScan devices provide wireless telemetry and Medtronic CareAlert
Monitoring using a patient monitor (if available). Astra MRI SureScan devices do not
provide these features.

●

Only those features that vary across device model are included in the following table. All
other features described in this manual are available for all Astra MRI SureScan and
Azure MRI SureScan models.

Table 1. Product feature relationship

Azure MRI SureScan and Astra MRI SureScan

XT DR S DR XT SR S SR

W1DR01

Features

X1DR01

AT/AF Burden Observations X X

AT/AF Detection X — — —

AT/AF Monitor X X — —

Atrial 50 Hz Burst In-Office X — — —

Atrial ATP X — — —

Atrial Preference Pacing X X — —

Atrial Rate Stabilization X — — —

Auto PVARP X X — —

Cardiac Compass X — X —

Capture Management - Atrial X X — —

Capture Management - RV X X X X

Conducted AF Response X — X —

Flashback Memory - Atrial Episodes X X — —

Flashback Memory- Ventricular Epi-

X X X X

sodes

Mode Switch X X — —

Non-Competitive Atrial Pacing X X — —

Pacing modes - atrial (AAIR, AAI, AOO) X X — —

Pacing modes - dual chamber (DDDR,

X X — —

DDD, DDIR, DDI, DOO, ODO)

Pacing modes - MVP (AAIR<=>DDDR,

X X — —

AAI<=>DDD)

Pacing modes - ventricular (VVIR, VVI,

X X X X

VOO, OVOb)

Patient-activated symptom log entries X — X —

PMT Intervention X X — —

W3DR01

X3DR01

a

W1SR01

X1SR01

— —

W3SR01

X3SR01

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Table 1. Product feature relationship (continued)

Azure MRI SureScan and Astra MRI SureScan

XT DR S DR XT SR S SR

W1DR01

Features

X1DR01

Post-Mode Switch Overdrive Pacing X — — —

PVC Response X X — —

Rate Adaptive AV X X — —

Rate Drop Response X X — —

Reactive ATP X — — —

TherapyGuide X X — —

Ventricular Rate Stabilization X — X —

Ventricular Safety Pacing X X — —

a

AT/AF Burden Observations are available for W3DR01 devices only as clinical status alerts for the Medtronic
CareAlert Monitoring feature. AT/AF Burden Observations are not available for X3DR01 devices.

b

OVO mode is only available in single-chamber device models.

W3DR01

X3DR01

W1SR01

X1SR01

W3SR01

X3SR01

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2 Patient follow-up guidelines

2.1 In-clinic follow-up appointments and remote monitoring

Schedule regular in-clinic follow-up appointments with the patient throughout the service life
of the device. For patients enrolled in the Medtronic CareLink Network, remote monitoring
can replace the need for some in-clinic follow-up appointments. With remote monitoring,
data from a patient’s implanted device is sent to the Medtronic CareLink Network, and you
can review the transmitted data on the Medtronic CareLink Network website. Schedule
in-clinic follow-up appointments and CareLink transmissions as follows:

●

Schedule an in-clinic follow-up appointment within 72 hours of implant so that the patient
can be checked for lead dislodgement, wound healing, and postoperative
complications.

●

Schedule an in-clinic follow-up appointment within 2−12 weeks after implant to evaluate
the condition of the patient, the device, and the leads, and to verify that the device is
configured appropriately for the patient.

●

Schedule routine CareLink transmissions or in-clinic follow-up appointments every
3−12 months, with in-clinic follow-up appointments occurring at least annually.

●

When the device battery approaches Recommended Replacement Time (RRT),
schedule CareLink transmissions or in-clinic follow-up appointments every 1−3 months.

●

Schedule in-clinic follow-up appointments as needed (for example, if data from a
CareLink transmission indicates that the patient’s device requires adjustment).

2.1.1 Remote monitoring options

Azure MRI SureScan devices provide automatic wireless remote monitoring using a
Medtronic patient monitor (if available). The transmissions occur automatically at a
scheduled date and time. You can schedule automatic transmissions on the Medtronic
CareLink Network website. In addition, automatic, unscheduled transmissions for specific
clinical or device status events are provided by the CareAlert Monitoring feature (see
Section 3.2, “Medtronic CareAlert Monitoring”, page 21). Patients can also send
unscheduled transmissions manually.

Astra MRI SureScan devices provide remote monitoring using a Medtronic patient monitor
(if available). Patients hold the monitor’s telemetry head over their implanted device and
initiate the transmission at the scheduled time. Patients can also send unscheduled
transmissions manually.

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Note: When viewing a CareLink transmission, the data collected since the last session is
presented differently than it is for a programmer session. For a CareLink transmission, the
last session is defined as either the last programmer session or the last CareLink
transmission. During an in-clinic follow-up appointment, the programmer software defines
the last session as the last programmer session.

2.1.2 Follow-up process

The process for conducting a follow-up evaluation, either during an in-clinic appointment or
with a CareLink transmission, includes the following steps:

1. Review the patient’s presenting rhythm.

2. Verify the status of the implanted system.

3. Verify the clinical effectiveness of the implanted system.

4. During an in-clinic follow-up appointment, adjust device parameters as necessary.

5. If evaluating data remotely, schedule an in-clinic follow-up appointment as necessary.

2.1.3 Reviewing the presenting rhythm

The presenting rhythm may indicate the presence of undersensing, far-field oversensing, or
loss of capture. These are basic pacing issues that can affect the delivery of therapy. These
issues can often be resolved by making basic programming changes.

Review the presenting rhythm as follows:

●

During an in-clinic follow-up appointment, view the Live Rhythm Monitor and record the
EGM and Marker Channel traces.

●

For remote monitoring, review the EGM data that was recorded at the time of the
CareLink transmission.

Viewing this information can help you identify any issues with the patient’s presenting
rhythm. It may be necessary to adjust the pacing parameters.

2.1.4 Verifying the status of the implanted system

Perform the following tasks to verify the status of the implanted system:

●

Assess the battery status.

●

Check lead measurement data.

●

Review any Quick Look II Observations about the device and lead status.

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2.1.4.1 Assessing the battery status

To assess the status of the device battery, review the Remaining Longevity estimate in the
Quick Look II data. If the device battery has reached a replacement threshold, the
associated indicator is displayed. For more detail about the battery status, including battery
voltage, review the Battery and Lead Measurements data as follows:

●

During an in-clinic follow-up appointment with a programmer, select the [>>] button next
to the Remaining Longevity field on the Quick Look II screen.

●

When evaluating a CareLink transmission, review the Battery and Lead Measurements
report.

Warning: Replace the device immediately if the End of Service (EOS) indicator is displayed.
The device may lose the ability to pace, sense, and deliver therapy adequately after the
battery reaches End of Service.

If the Recommended Replacement Time (RRT) indicator or Elective Replacement Indicator
(ERI) is displayed, or if the battery voltage is at or below the displayed RRT voltage, contact
your Medtronic representative and schedule a replacement procedure with your patient. For
more information about the replacement indicators, see Section 3.10, “Device and lead
performance data”, page 37.

2.1.4.2 Checking lead measurements and trend data

In-clinic follow-up appointment – During an in-clinic follow-up appointment, you can

check the status of the implanted leads by reviewing the Impedance, Threshold, and Wave
Amplitude trends on the Quick Look II screen. For a more detailed history of each
measurement, select the [>>] button next to the appropriate trend graph. For more
information about the automatic collection of these trends, see Section 3.10, “Device and
lead performance data”, page 37. If you also want to gather real-time information about the
performance of the device and leads, you can perform the following tests:

●

Lead Impedance Test

●

Pacing Threshold Test

●

Sensing Test

For more information about performing these tests, refer to the programming guide.

Evaluating a CareLink transmission – When evaluating a CareLink transmission, you can
check the status of implanted leads by reviewing the most recent lead impedance, capture
threshold, and sensing amplitude measurements on the Quick Look II report. Compare
these values to the patient history and to the trend data provided on the Lead Trends report.

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2.1.4.3 Reviewing Quick Look II Observations about the device and lead status

The Quick Look II data includes Observations that are based on an analysis of programmed
parameters and collected data. Observations may include information about the status of
the device and battery, the integrity of the implanted leads, or potential issues with
programmed parameter settings. If Medtronic CareAlert Monitoring is enabled, any alert
events detected by the device are presented as Quick Look II Observations. Review the
Observations and check related reports for evidence of a problem with the device or leads.

2.1.5 Verifying the clinical effectiveness of the implanted system

Perform the following tasks to verify the clinical effectiveness of the implanted system:

●

Review any Quick Look II Observations about the patient’s clinical status

●

Assess the effectiveness of pacing therapy

●

Check tachyarrhythmia episode records for appropriate detection and therapy

2.1.5.1 Reviewing Quick Look II Observations about clinical status

The Quick Look II data includes Observations about noteworthy or abnormal patient
conditions such as low patient activity, unexpectedly high rates, or high arrhythmia burden.
If Medtronic CareAlert Monitoring is enabled, any alert events detected by the device are
presented as Quick Look II Observations. Review the Observations and check related data
to help evaluate the clinical effectiveness of the implanted system.

2.1.5.2 Assessing the effectiveness of pacing therapy

1. Review the pacing percentages in the Quick Look II data. To assess the patient’s pacing
and sensing history in more detail, review the Rate Histograms data. For more
information, see Section 3.9, “Rate Histograms”, page 36.

2. Review Cardiac Compass Trends data and compare it with the patient history. Cardiac
Compass Trends data can help you to determine whether changes in the patient’s
activity, pacing therapies, and arrhythmias have occurred during the past 14 months.
For more information about the data collected by the Cardiac Compass Trends feature,
see Section 3.3, “Cardiac Compass Trends”, page 24.

3. Evaluate the patient’s pacing thresholds by reviewing capture threshold trend data or,
for in-clinic follow-up appointments, by performing a Pacing Threshold Test. Check the
programmed pacing parameters to ensure they provide an appropriate safety margin.

4. During in-clinic follow-up appointments, interview the patient to confirm that the patient
is receiving adequate cardiac support for daily living activities.

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2.1.5.3 Assessing tachyarrhythmia detection and therapy

1. Review the Quick Look II data for the counts of each kind of tachyarrhythmia episode.

2. Evaluate AT/AF burden by reviewing the Cardiac Compass Trends data and the Rate
Histograms data. For more information, see Section 3.3, “Cardiac Compass Trends”,
page 24 and Section 3.9, “Rate Histograms”, page 36.

3. Check tachyarrhythmia episode records to evaluate detection accuracy and the
effectiveness of any delivered tachyarrhythmia therapy. For more information about the
data provided in episode records, see Section 3.4, “Arrhythmia Episodes data”,
page 28.

2.1.6 Adjusting device parameters

Adjust the pacing, tachyarrhythmia detection, tachyarrhythmia therapy, and diagnostic data
parameters as needed to address any issues identified during the follow-up appointment.

Caution: Use caution when reprogramming the detection or sensing parameters to ensure
that appropriate sensing is maintained. For more information, see Section 4.1, “Sensing”,
page 43 .

2.1.7 Scheduling an in-clinic follow-up appointment

Data transmitted to the Medtronic CareLink Network may indicate the need to schedule an
in-clinic follow-up appointment with your patient in addition to their regularly scheduled
appointments. You may need to perform manual tests, adjust device parameters, or assess
lead status more directly. The following table shows an example of how data from a CareLink
transmission may be used to make scheduling decisions.

Table 2. Example: Responses to different kinds of CareLink transmissions

Device and lead
status Clinical status

Normal Normal According to the regular schedule
Normal Abnormal, but no urgent or emer-

gency conditions
Normal Abnormal, urgent condition Within 1 week
Normal Abnormal, emergency condition Immediately
Abnormal Any Immediately

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When to schedule an in-clinic fol­low-up appointment

According to the regular schedule

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

2.2 Optimizing device longevity

Optimizing device longevity is a desirable goal because it may reduce the frequency of
device replacement for patients. Optimizing device longevity requires balancing the benefit
of device therapy and diagnostic features with the energy requirements placed on the battery
as a result of these features.

To view the Remaining Longevity estimate for the device, refer to the Quick Look II screen.

The following sections describe strategies that may help reduce the energy requirements
placed on the battery.

2.2.1 Promoting intrinsic AV conduction

Managed Ventricular Pacing (MVP) – The MVP feature promotes AV conduction by

reducing unnecessary right ventricular pacing. The primary benefit of the MVP feature is
therapeutic, but it may also preserve device longevity as a result of a decrease in the
percentage of pacing. For more information about the MVP feature, see Section 4.5,
“Managed Ventricular Pacing (MVP)”, page 66.

Promoting AV conduction with longer AV intervals – Another method of promoting AV
conduction is to increase the Paced AV and Sensed AV intervals. This allows intrinsic
conduction to occur before a ventricular pace. Fewer pacing pulses may help to preserve
device longevity. For more information, see Section 4.2, “Basic pacing”, page 53.

2.2.2 Managing pacing outputs

Capture Management – The Capture Management feature provides the device with

automatic monitoring and follow-up capabilities for managing pacing thresholds. This
feature is designed to monitor the pacing threshold and, optionally, to adjust the pacing
outputs to maintain capture. Programming the Capture Management feature allows the
device to set the pacing amplitude just high enough to maintain capture while preserving
battery energy. For more information, see Section 4.7, “Capture Management”, page 77.

Manual optimization of amplitude and pulse width – If you choose to program the
Capture Management feature to Off, you can optimize the patient’s pacing output
parameters manually. Perform a Pacing Threshold Test to determine the patient’s pacing
thresholds. Select amplitude and pulse width settings that provide an adequate safety
margin above the patient’s pacing threshold. These actions decrease the pacing outputs
and preserve battery energy. Refer to the programming guide for more information about
performing a Pacing Threshold Test.

Pacing rate – The more paced events that are delivered, the more device longevity is
reduced. Make sure that you have not programmed an unnecessarily high pacing rate for the
patient. Carefully consider using features that increase bradycardia pacing rate. Use

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features such as Atrial Preference Pacing (APP), Conducted AF Response, and Rate
Response only for patients who can receive therapeutic benefit from the feature.

2.2.3 Disabling Atrial Sensitivity

Atrial Sensitivity – When atrial monitoring is not needed due to chronic AT/AF, consider

programming Atrial Sensitivity to Off before changing the mode to VVI or VVIR to preserve
battery energy.

Note: When Atrial Sensitivity is programmed to Off, AT/AF monitoring is disabled.

2.2.4 Considering how diagnostic features with data storage impact longevity

Pre-arrhythmia EGM storage – Continual use of Pre-arrhythmia EGM storage reduces

device longevity. For a patient with uniform tachyarrhythmia onset mechanisms, the greatest
benefit of Pre-arrhythmia EGM storage is obtained after capturing a few episodes.

When Pre-arrhythmia EGM storage is on, the device collects up to 20 s of EGM data before
the onset of VT Monitor or SVT episodes.

Note: The Pre-arrhythmia EGM feature does not apply to AT/AF episodes. The device stores
approximately 4 s of EGM before AT/AF detection regardless of the Pre-arrhythmia EGM
storage setting.

To balance the benefit of using the Pre-arrhythmia EGM storage feature with optimizing
device longevity, consider the following programming options:

●

Program Pre-arrhythmia EGM storage to On-1 month, On-3 months, or On Continuous
to capture possible changes in the tachyarrhythmia onset mechanism following
significant clinical adjustments such as device implant, medication changes, and
surgical procedures. Select the setting for the shortest time period that will provide the
necessary data.

●

Program Pre-arrhythmia EGM storage to Off after you have obtained the data of interest.

Note: When Pre-arrhythmia EGM storage is off, the device begins to store EGM information
for VT Monitor and SVT episodes after the third tachyarrhythmia event occurs. Though EGM
is not recorded before the start of the arrhythmia, the device still records up to 20 s of data
before the onset or detection of the episode. This data includes interval measurements and
Marker Channel annotations. In addition, Flashback Memory data is stored for the most
recent tachyarrhythmia episodes.

Holter telemetry – Extended use of the Holter telemetry feature decreases device
longevity. The Holter telemetry feature continues to transmit EGM and Marker Channel data
for the programmed time duration regardless of whether the programming head is
positioned over the device.

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Medtronic CareLink remote transmissions – When scheduling Medtronic CareLink
remote transmissions, be aware that increasing the frequency of remote transmissions
reduces implanted device service life. Refer to the device manual for more information about
the estimated effect on a specific device model. To conserve battery energy, schedule the
lowest frequency of remote transmissions that still allows for the desired monitoring of your
patient’s device.

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3 Diagnostic data features

3.1 Quick Look II summary data

At the start of a patient session, it is useful to quickly view summary information about device
operation and the patient’s condition. This overview can help you to determine whether you
need to look more closely at diagnostic data or reprogram the device to optimize therapy for
the patient.

The Quick Look II data summarizes the most important indicators of system operation and
the patient’s condition. These indicators include device and lead status data, pacing therapy
information, arrhythmia episode data, and system-defined observations.

You can view Quick Look II data on the Quick Look II screen, which is displayed on the
programmer at the beginning of a patient session. To return to the Quick Look II screen from
another screen, select Data > Quick Look II. For more information about using the Quick
Look II screen, refer to the programming guide.

3.1.1 Quick Look II device and lead status information

The Quick Look II data includes the following information about device and lead status:

●

Estimate of remaining battery longevity

●

Trends of the weekly average impedance, capture threshold, and wave amplitude
measurements

●

Most recent measured values for impedance, capture threshold, and wave amplitude

3.1.2 Quick Look II pacing therapy information

The Quick Look II data includes the following information about pacing therapy:

●

programmed values for the Mode, Lower Rate, and Upper Tracking Rate parameters

●

percentage of time spent pacing since the last patient session

●

an indication that the pacing mode is currently programmed to an MVP mode (“MVP
On”) or to another pacing mode (“MVP Off”).

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3.1.3 Quick Look II arrhythmia episode information

The Quick Look II data includes the following information about arrhythmia episodes since
the last patient session:

●

percentage of time spent in AT/AF

●

number of AT/AF episodes treated with tachyarrhythmia therapy

●

number of monitored VT episodes

●

number of monitored Fast A&V episodes

●

number of monitored AT/AF episodes

3.1.4 Quick Look II Observations

Observations are based on an analysis of programmed parameters and data collected since
the last session. The following types of observations may occur:

●

Device status observations inform you of conditions that affect device operation and
require attention. Examples of such conditions include Recommended Replacement
Time (RRT) or the occurrence of a device reset.

●

Lead status observations report any potential issues with the sensing integrity of the
leads, possible lead dislodgments, and abnormal Capture Management results. You
may also be warned about possible inconsistencies in the programming of lead polarity.

●

Parameter observations warn of any inconsistencies in the programming of detection
and therapy parameters. An example is certain parameter settings resulting in a therapy
being disabled.

●

Diagnostic data observations report noteworthy arrhythmia episodes. Examples include
arrhythmias of different types occurring together and episodes for which therapies were
unsuccessful. Conditions that prevent diagnostic data from being collected effectively
are also reported.

●

Medtronic CareAlert observations can report system or device performance conditions
and certain heart rhythm conditions. For more information, see Section 3.2, “Medtronic
CareAlert Monitoring”, page 21.

●

Clinical status observations alert you to abnormal patient conditions, such as low activity
rates, unexpectedly high heart rates, or high arrhythmia burden.

On the Quick Look II screen, if you select one of the displayed observations and more
information about the selected observation is available, the [>>] button becomes active. You
can use the [>>] button to look at relevant details.

Setting parameters for clinical status Observations – The Medtronic CareAlert
Monitoring feature includes clinical status alerts related to high arrhythmia burden (see

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Section 3.2, “Medtronic CareAlert Monitoring”, page 21). For Astra XT DR MRI SureScan
devices, or for Azure XT DR MRI SureScan devices with the Wireless Telemetry with Monitor
parameter programmed to Off, the system provides this information as Quick Look II
Observations. The device records an Observation in the Quick Look II data if either the AT/AF
burden or the ventricular heart rate during AT/AF exceed a programmed threshold. The
threshold parameters are programmed from the Data Collection Setup screen.

Table 3. How to navigate to parameters for clinical status Observations

Parameters Path

AT/AF Daily Burden
Avg. V. Rate During AT/AF Burden
Avg. V. Rate During AT/AF V. Rate

Params > Data Collection Setup… > AT/AF Set­tings…

3.2 Medtronic CareAlert Monitoring

Important clinical management and system performance events may occur between
scheduled patient sessions. These events may relate to clinical management data or system
issues that should be investigated. The early detection and notification of these events,
should they occur, enable you to intervene promptly with appropriate care for your patient.

The Medtronic CareAlert Monitoring feature automatically sends alert data about specified
clinical management and system performance events to the Medtronic CareLink Network
through a Medtronic patient monitor (if available). Depending on the severity of the alert
condition, you can set up Medtronic CareAlert notifications through the CareLink Network to
hold the alert for routine review on the CareLink website, or to notify you via email, voice
message, text message, or pager.

3.2.1 Operation of Medtronic CareAlert Monitoring

If the Wireless Telemetry with Monitor parameter is programmed to On, the Medtronic
CareAlert Monitoring feature is available. If a clinical or system performance event occurs
and Medtronic CareAlert Monitoring is programmed to respond with an alert, the device
automatically attempts to establish wireless communication with the monitor. After
communication is established, the monitor receives the alert data from the device, and then
transmits the alert data to the CareLink Network. The CareLink Network records the alert,
and you are notified based on your preferences. If the transmission is unsuccessful at first,
the device and monitor periodically repeat the process until the transmission is successfully
sent.

Note: After a wireless alert signal has been successfully transmitted, the device does not
retransmit data for that particular alert until the alert is cleared. This is true even if the
threshold for the alert is met again in the interim.

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The CareAlert notification methods (any one or a combination of voice message, text
message, pager, email, or website-only) are set on a per-clinic basis according to alert
urgency and time of day. You can assign the level of urgency to each alert for individual
patients, so that the same alert can be high urgency for one patient and low urgency for
another patient.

3.2.1.1 Clinical management event alerts

AT/AF Daily Burden > Threshold – This alert indicates that the cumulative time in AT/AF

exceeds the programmed threshold.

Avg. V. Rate During AT/AF > Threshold – This alert indicates that the average ventricular
rate during a selectable duration of AT/AF exceeds the programmed threshold.

Monitored VT Episode Detected – This alert indicates that one or more monitored VT
episodes were detected.

Cumulative Right Ventricular Pacing > 40% – This alert indicates that the cumulative
percentage of right ventricular pacing exceeded 40% for 7 consecutive days.

3.2.1.2 System performance event alerts

Low Battery Voltage Recommended Replacement Time – This alert indicates that the

daily automatic battery voltage measurement has been at or below the Recommended
Replacement Time voltage level for 3 consecutive days.

Lead Impedance Out of Range – This alert indicates that the daily lead impedance
measurement for one of the implanted leads is out of range. This could indicate that the lead
has dislodged or is improperly connected.

Capture Management High Threshold – These alerts indicate that 3 consecutive daily
capture threshold measurements in the specified chamber were high.

Device Reset (nonprogrammable) – This alert indicates that the device has been reset.
Diagnostic data may have been cleared and parameters may require reprogramming.
Immediately contact your Medtronic representative if a device reset occurs. For device reset
parameter values, see the parameter tables in the device manual for the specific device
model.

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3.2.2 Programming Alerts

Table 4. How to navigate to CareAlert parameters

Parameters Path

Wireless Telemetry with Monitor Params > Data Collection Setup

Monitored VT Episode Detected
Cumulative Right Ventricular Pacing > 40%
Low Battery Voltage RRT

AT/AF Burden and Rate alert parameters:

AT/AF Daily Burden Enable
AT/AF Daily Burden
Avg. V. Rate During AT/AF Enable
Avg. V. Rate During AT/AF Burden
Avg. V. Rate During AT/AF V. Rate

Lead Impedance Out of Range alert param­eters:

A. Pacing Enable
A. Pacing Less than
A. Pacing Greater than
RV Pacing Enable
RV Pacing Less than
RV Pacing Greater than

Capture Management High Threshold
parameters:

A. Capture Enable
RV Capture Enable

Params > Alert…

Params > Alert… > AT/AF Burden and Rate Set­tings…

Params > Alert… > Lead Impedance Out of
Range…

Params > Alert… > Capture Management High
Threshold…

Programming alert parameters – The Wireless Telemetry with Monitor parameter must be
set to On before you can program Medtronic CareAlert Monitoring parameters.

Repetitive alerts – If a programmable alert is triggered so often that it loses its clinical value,
consider adjusting the alert threshold, programming the device to improve therapy
effectiveness, or disabling the alert.

3.2.3 Evaluation of alert events

The device stores alert events in the Medtronic CareAlert Events log. For each alert event,
a log entry includes the date and time of the alert, a description of the event, and the
measurement or information that caused the event. Up to 15 alert events are stored.

To access alert events, select Data > CareAlert Events.

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3.3 Cardiac Compass Trends

An analysis of clinical information collected over a long term can help you to follow changes
in a patient’s condition and correlate these changes with variations in device programming,
medication, patient activity, or symptoms.

Cardiac Compass Trends data provides information about a patient’s condition over the last
14 months. Graphs show trends in tachyarrhythmias, physical activity, heart rates, device
therapies, and information related to heart failure. Dates and event annotations allow you to
correlate trends from different graphs. The trends can also help you to assess whether
device therapies or antiarrhythmic drugs are effective.

Data storage for the Cardiac Compass Trends feature is automatic. No setup is required. The
device begins storing data after the device is implanted. Each day thereafter, the device
stores a set of trend data. After 14 months of data are collected, the device continues storage
by overwriting the oldest stored data with new data.

Note: The schedule for collecting daily measurements and the time annotations displayed
in the trends are both based on the device clock.

To access Cardiac Compass Trends data, select Data > Clinical Diagnostics >
Cardiac Compass Trends > [Open Data].

3.3.1 Information provided by Cardiac Compass Trends

The Cardiac Compass Trends data includes the following types of information:

●

Programming and interrogation event annotations

●

Trend graphs related to AT/AF burden

●

Trend graphs related to pacing and patient activity

●

Trend graphs related to heart failure

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3.3.1.1 Event information

Figure 1. Event annotations

1 Current session indicator
2 Last session indicator

Programming and interrogation events – Cardiac Compass Trends data includes
annotations showing when the device was interrogated or programmed to allow possible
correlations between device parameter changes and other clinical trends.

When the patient is evaluated during an office visit, an “I” annotation is added for a day on
which the device is interrogated and a “P” annotation is added for a day on which any
programmable parameter is changed (except for temporary changes). If the device is
interrogated and programmed on the same day, only a “P” is displayed.

When the patient is evaluated during a remote monitoring session, an “I” annotation with a
line beneath it is added to the data.

A vertical line runs through all the graphs to indicate the beginning of the current session. If
applicable, the last session is also marked with a vertical line.

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3.3.1.2 AT/AF burden information

Figure 2. AT/AF arrhythmia trend graphs

AT/AF total hours per day – This trend may help you to assess the need to adjust the

patient’s device or drug-based therapies. This trend may also reveal the presence of
asymptomatic episodes of AT/AF.

The device records a daily total for the time the patient spent in atrial arrhythmia. The time in
AT/AF is calculated from the point of AT/AF Onset. This trend may be reported in hours (0 to

24) or minutes (0 to 60) per day depending on the maximum duration per day. For more
information, see Section 5.1, “AT/AF detection”, page 124.

Ventricular rate during AT/AF – You can use this trend to perform the following
assessments:

●

Correlate patient symptoms to rapid ventricular responses to AT/AF.

●

Prescribe or titrate antiarrhythmic and rate control drugs.

●

Assess the efficacy of an AV node ablation procedure.

The graph plots average ventricular rates during episodes of atrial arrhythmia each day. The
vertical lines show the difference between the average rate and the maximum sensed
ventricular rate each day.

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3.3.1.3 Pacing and patient activity information

Figure 3. Pacing and patient activity trend graphs

Percent pacing per day – This trend provides a view of pacing over time that can help you

to identify pacing changes and trends. The graph displays the percentage of all events
occurring during each day that are atrial paces and ventricular paces. The percentages are
calculated from the daily counts of each event type.

Average ventricular rate – The day and night heart rates provide information that may have
the following clinical uses:

●

objective data to correlate with patient symptoms

●

indications of autonomic dysfunction or symptoms of heart failure

●

information regarding diurnal variations

For this trend, “day” is defined as the 12-hour period between 08:00 and 20:00 and “night” as
the 4-hour period between 24:00 and 04:00 (as indicated by the device clock).

Patient activity – The patient activity trend may provide the following information:

●

information about a patient’s exercise regimen

●

an objective measurement of patient response to changes in therapy

●

an early indicator of progressive diseases like heart failure, which cause fatigue and a
consequent reduction in activity

The patient activity trend is a 7-day average of data derived from the device rate response
accelerometer. It is reported only after 14 days of data have been collected.

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3.3.1.4 Heart failure information

Figure 4. Heart rate variability trend

Heart rate variability – Reduced variability in the patient’s heart rate may help you to

identify heart failure decompensation. The device measures each atrial interval and
calculates the median atrial interval every 5 min. It then calculates and plots a variability
value (in ms) for each day.

Note: The heart rate variability calculation does not include events that occur during
arrhythmia episodes.

3.4 Arrhythmia Episodes data

The device stores several different types of data for arrhythmia episodes. The episode log
summarizes key data for each episode. Episode records include more detailed information
for each episode, including an interval plot, stored EGM, and episode text.

To access Arrhythmia Episodes data, select Data > Clinical Diagnostics >
Arrhythmia Episodes > [Open Data]. For more information about using the Arrhythmia
Episodes screen, refer to the programming guide.

3.4.1 Episode log

The device stores the following summary information for each arrhythmia episode:

●

type of episode

●

the number of ATP sequences delivered (if any)

●

whether the last therapy delivered was successful

●

the date, time, and duration of the episode

●

the average atrial and ventricular rates during the episode

●

the maximum ventricular rate during the episode

●

whether EGM data is available for the episode

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Calculating the average rate – For AT/AF, VT Monitor, VT-NS, and Fast A&V episodes, the
average atrial and ventricular rates are calculated from the average cycle lengths throughout
the entire episode. For SVT episodes, the average atrial and ventricular rates are an average
of the 4 beats at detection or just prior to withholding detection.

Display of the maximum ventricular rate – If the ventricle was paced during an AT/AF
episode, the maximum ventricular rate appears in the log as VP. For VT-NS episodes, the
maximum ventricular rate value is not displayed.

Patient-Activated Symptom Log entries – If the patient has a Medtronic patient assistant
instrument, you can instruct them to use their patient assistant to record a Symptom entry in
the arrhythmia episode log. This log entry will include the date, time, and average atrial and
ventricular cycle lengths. If an arrhythmia episode is already in progress when the patient
records a Symptom episode, the device does not store an additional log entry. Instead, the
episode text for the ongoing arrhythmia episode is annotated with the statement “Patient
Symptom detected during episode.”

Notes:

●

Episodes that occur during a device session are not available to view in the episode
records until an interrogation is performed. The interrogation must be performed after
episode termination.

●

For each episode type, when the log capacity is reached, data from the most recent
episodes overwrites the oldest episode data in the log.

3.4.2 Episode records

The device stores detailed information about the arrhythmia episodes recorded in the
episode log. An arrhythmia episode record contains the following information:

●

an interval plot

●

a strip chart of the stored EGM (if available)

●

a text summary

●

Flashback Memory data (if available)

3.4.2.1 Episode interval plot

The device records the durations of the V-V and A-A intervals that occur during the episode.
The episode interval plot graphs these interval durations versus time. The episode interval
plot also includes the following information for an episode:

●

programmed detection intervals

●

point of onset, for AT/AF episodes

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●

point of detection or detection withheld

●

points of therapy delivery

Note: The device may truncate data storage during an episode to conserve device memory.

3.4.2.2 Episode EGM

The device receives EGM data on three separate channels: EGM1, EGM2, and EGM3. The
Source parameter for each channel defines the electrodes between which the device
records the EGM signal. The Range parameters define the upper and lower amplitude limits
of each recorded signal in mV. Using the Monitored parameter, you can select a set of 2 EGM
channels for arrhythmia episode record storage.

The EGM data for each episode record is accompanied by the following additional
information:

●

Marker Channel annotations, showing the classification of cardiac events by the device

●

Interval measurements

●

Decision Channel annotations, identifying when tachyarrhythmia detection occurred,
and which type of rhythm was detected:

– VTM: monitored VT episode

– VTM+SVT: monitored VT episode with SVT

– Fast A&V: simultaneous atrial and ventricular tachyarrhythmias

– AT/AF Detection: detected AT or AF episode

– Fast AT/AF Detection: detected AT or AF episode with a rate in the Fast AT/AF zone

To conserve device memory, EGM data is stored only during specific parts of an episode:

●

prior to episode detection

●

before and after the first tachyarrhythmia therapy is delivered

●

prior to episode termination

As a result, long episodes may contain gaps in the EGM between these events.

When the Pre-arrhythmia EGM feature is enabled, the device continuously collects EGM
data, providing up to 20 s of EGM data for storage prior to the detection of VT Monitor, SVT,
VT-NS, and Fast A&V episodes. When the Pre-arrhythmia EGM feature is programmed to
Off, the device stores EGM data for these episodes starting after the third tachyarrhythmia
event occurs. Though EGM is not recorded before the start of the arrhythmia, the device still
records up to 20 s of interval measurements and Marker Channel annotations.

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Note: The Pre-arrhythmia EGM feature does not apply to AT/AF episodes. The device stores
approximately 4 s of EGM data prior to AT/AF detection, regardless of Pre-arrhythmia EGM
operation.

3.4.2.3 Episode text

The device stores details with each episode record that are displayed in text form:

●

episode number

●

episode type

●

date, time, and duration of the episode

●

maximum atrial and ventricular rates during the episode

●

median atrial or ventricular rate during the episode (depending on the episode type)

●

patient activity at the onset of the episode, along with the calculated sensor rate
associated with the level of activity

●

programmed parameter settings related to sensing, tachyarrhythmia detection,
tachyarrhythmia therapy, and EGM sources

●

for treated AT/AF episodes, the sequence of ATP therapies and a summary of the
number of ATP therapies delivered

3.4.2.4 Flashback Memory data

The episode records for the most recent VT, Fast A&V and AT/AF episodes provide
Flashback Memory data. This data includes up to a total of 2000 V-V and A-A intervals and
stored marker data. For more information, see Section 3.6, “Flashback Memory data”,
page 34.

3.4.3 Programming Arrhythmia Episodes data collection

Arrhythmia episode data collection is automatic when tachyarrhythmia detection features
are programmed to On or Monitor. Parameters that control EGM data storage are available
on the Data Collection Setup screen.

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Table 5. How to navigate to parameters for arrhythmia episode data collection

Parameters Path

EGM1 Source
EGM1 Range
EGM2 Source
EGM2 Range
EGM3 Source
EGM3 Range
Monitored
Pre-arrhythmia EGM

Params > Data Collection Setup…

EGM settings and Live Rhythm Monitor – The signals displayed on the Live Rhythm
Monitor for the EGM1, EGM2, and EGM3 waveform traces are controlled by the
corresponding EGM Source and EGM Range parameters.

EGM source and sensing – The cardiac interval measurements of the device are always
based on the signals sensed through the programmed sensing polarity (not the stored
diagnostic EGM). Therefore, your selection of EGM sources does not affect bradycardia
pacing or tachyarrhythmia detection.

EGM range – The EGM range setting affects the resolution of the EGM signal; the lower the
setting, the higher the resolution. If the EGM signal is illegible or clipped, consider changing
the range selection.

Pre-arrhythmia EGM – Pre-arrhythmia EGM storage works by keeping the EGM circuitry
enabled at all times, and therefore it reduces device longevity. If you select On - 1 Month or
On - 3 Months, Pre-arrhythmia EGM storage is automatically turned off after the time period
expires.

3.5 Episode and therapy counters

The device stores data about the number of times VT/VF episodes, AT/AF episodes, and
therapies have occurred. The counter data for ventricular episodes includes counts of
ventricular episodes of different types, counts of premature ventricular contractions (PVCs),
and counts of Ventricular Rate Stabilization (VRS) paces. The counter data for atrial
episodes includes information about the amount of time spent in AT/AF, counts of different
types of atrial episodes, and information about the time spent in atrial pacing and atrial
intervention pacing. The counter data for atrial therapies includes counts of treated atrial
episodes and the percentage of time the therapies successfully terminated episodes,
grouped by therapy type and atrial cycle length.

To access the episode and therapy counters, select Data > Clinical Diagnostics > Counters >
[Open Data].

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3.5.1 VT/VF episode counters

The device records the following types of counter data related to ventricular arrhythmias
since the last session, and for the lifetime of the device:

VT – The number of VT Monitor episodes.

VT-NS – The number of non-sustained ventricular tachyarrhythmias.

Fast A&V – The number of Fast A&V and SVT episodes.

PVC Runs – The average number of runs per hour of premature ventricular contractions

(PVCs) in which 2, 3, or 4 consecutive ventricular events are premature.

PVC Singles – The average number of single PVCs per hour. PVCs in PVC runs are not
counted as PVC singles.

Runs of VRS Paces – The average number of times per hour that 2 or more consecutive
ventricular events are Ventricular Rate Stabilization (VRS) pacing pulses (VRS escape
interval timeouts).

Single VRS Paces – The average number of single VRS pacing pulses (VRS escape
interval timeouts) per hour. VRS paces in runs of VRS paces are not counted as single VRS
paces.

3.5.2 AT/AF episode counters

The device records the following types of counter data related to atrial arrhythmias since the
last session, and for the lifetime of the device:

% of Time AT/AF – The percentage of total time in AT/AF. AT/AF is defined as starting from
AT/AF onset. The device additionally stores this data for the period between last session and
the session prior to the last session.

Average AT/AF time/day – The average time in AT/AF per day. AT/AF is defined as starting
from AT/AF onset. The device additionally stores this data for the period between last
session and the session prior to the last session.

Monitored AT/AF Episodes – The average number of monitored AT/AF episodes per day.
AT/AF is defined as starting from AT/AF detection.

Treated AT/AF Episodes – The average number of treated AT/AF episodes per day. AT/AF
is defined as starting from AT/AF detection.

Pace-Terminated Episodes – The percentage of pace-terminated AT/AF episodes for the
session. AT/AF is defined as starting from AT/AF detection.

% of Time Atrial Pacing – The percentage of time that atrial pacing was performed.

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% of Time Atrial Intervention – The percentage of time that atrial pacing was performed
due to atrial intervention pacing (Atrial Rate Stabilization or Atrial Preference Pacing). This is
a percentage of total time, not a percentage of atrial pacing time.

AT-NS – The average number of non-sustained AT (AT-NS) episodes per day.

3.5.3 AT/AF therapy counters

The device records the following types of counter data related to atrial tachyarrhythmia
therapies since the last session:

Fast AT/AF Rx – The number of episodes for which therapy was delivered (by therapy type)
and the percentage of successfully terminated episodes per therapy.

AT/AF Rx – The number of episodes for which therapy was delivered (by therapy type) and
the percentage of successfully terminated episodes per therapy.

Treated episodes by cycle length – The number of treated episodes and the percentage
terminated, in 7 groups of cycle lengths.

ATP Sequences – The number of atrial ATP sequences that were delivered and the number
that were aborted.

3.6 Flashback Memory data

Flashback Memory records atrial and ventricular intervals that occur immediately prior to
tachyarrhythmia episodes or the most recent interrogation. The feature plots the interval
data over time and allows you to view and print a graph of the collected data. The graphed
data may help you assess the patient’s heart rhythm and the performance of other features
such as Rate Response.

Flashback Memory automatically records up to a total of 2000 V-V and A-A intervals and
stored marker data for the following events:

●

the most recent interrogation

●

the most recent VT episode

●

the most recent Fast A&V episode

●

the most recent AT/AF episode

If 2 or more episodes are detected within 15 min, the Flashback Memory data before the
episodes may be truncated.

To access Flashback Memory data for the most recent VT, Fast A&V, or AT/AF episode,
select [Flashback] from the record details screen for the episode. Flashback Memory data
prior to the most recent interrogation is available from the Clinical Diagnostics screen.

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3.7 Rate Drop Response Episodes

Rate Drop Response is a pacing feature that monitors the heart for significant rate drops and
responds by pacing the heart at an elevated rate (see Section 4.10, “Rate Drop Response”,
page 91). When Rate Drop Response is programmed to On, the device records data about
episodes that meet the programmed rate drop detection criteria. This data is useful for
analyzing Rate Drop Response episodes and the events leading up to them. You can view
and print data for the last 10 episodes.

The device stores the following summary information for each Rate Drop Response episode:

●

type of episode (Drop Detection or Low Rate Detection)

●

date and time of the episode

●

ventricular rate at the point of detection

●

peak ventricular rate before detection (Drop Detection episodes only)

The following detailed information is provided for each Rate Drop Response episode:

●

an interval plot showing the durations of V-V and A-A intervals that occur during the
episode

●

a strip chart view showing Marker Channel annotations for the events that occur during
the episode

●

a text summary of the Rate Drop Response settings that were in effect at the start of the
programming session

To access Rate Drop Response episode data, select Data > Clinical Diagnostics > Rate
Drop Response Episodes > [Open Data].

3.8 MVP Mode Switches data

The MVP pacing modes reduce unnecessary ventricular pacing by providing AAI(R) mode
pacing when AV conduction is intact, and switching to DDD(R) mode if AV conduction is lost.
For more information about the MVP pacing modes (AAIR<=>DDDR and AAI<=>DDD), see
Section 4.5, “Managed Ventricular Pacing (MVP)”, page 66.

When the device is programmed to an MVP pacing mode and switches from AAI(R) to
DDD(R) mode, it records an MVP mode switch entry, which includes the following
information:

●

type of mode switch

●

date and time when the mode switch occurred

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●

median ventricular rate at the time of the mode switch

●

AV interval at the time of the mode switch

The device stores entries for up to the 10 most recent MVP mode switches to DDD(R) mode.
The MVP Mode Switches data is displayed with annotations showing the dates of
programmer and patient monitor sessions. It also includes a count of MVP mode switches
since the last session.

To access the MVP Mode Switches data, select Data > Clinical Diagnostics > MVP Mode
Switches > [Open Data].

3.9 Rate Histograms

Information about heart rates recorded between patient sessions can help you to monitor a
patient’s condition to assess the effectiveness of therapies. Rate Histograms shows the
distribution of atrial and ventricular rates recorded Since Last Session and Prior to Last
Session.

To access the Rate Histograms data, select Data > Clinical Diagnostics > Rate Histograms >
[Open Data].

3.9.1 Information provided by Rate Histograms

Rate Histograms report the atrial and ventricular event data stored by the device. There are
histograms for 3 types of heart rate data: atrial rate, ventricular rate, and ventricular rate
during AT/AF. They also report data about the patient’s conduction status. The histograms
include data from the current and previous collection periods. Data storage for Rate
Histograms is automatic; no setup is required.

Rate histograms show the percentage of time that the device was pacing and sensing within
rate ranges. There are 20 rate ranges that are each 10 bpm in length. Rates slower than
40 bpm are included in the “<40” range; rates faster than 220 bpm are included in the “>220”
range.

% of Time – This section shows the percentage of the total time that the device provided
pacing therapy during the collection period. This section excludes data about events that
occurred during AT/AF episodes. Dual-chamber devices include data showing the
percentage of time that AS-VS, AS-VP, AP-VS, and AP-VP event sequences occurred.

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Notes:

●

The AS-VS and AS-VP percentages include any sequences that began with an event
other than an atrial paced event.

●

If the patient experienced AT/AF for more than 99% of the time during the collection
period, the % of Time section displays this fact instead of the event sequence
percentages.

Atrial rate histogram – The atrial rate histogram shows the rate distribution of atrial sensed
and paced events (including sensed events that occur during the refractory period).

Ventricular rate histogram – The ventricular rate histogram shows the rate distribution of
ventricular sensed and paced events.

Ventricular rate during AT/AF histogram – The ventricular rate during AT/AF histogram
shows ventricular sensed and paced events that occurred during detected atrial
arrhythmias, and the total time in AT/AF1. This histogram may be used to monitor the
effectiveness of ventricular rate control therapy and drug titration.

3.10 Device and lead performance data

The device automatically measures and records device and lead performance data every
day. This information can help you assess the status of the device battery and identify issues
with lead position or lead integrity. The device records the following types of performance
data:

●

Remaining Longevity estimate and replacement indicators

●

Lead impedance measurements

●

Sensing amplitude measurements

●

Capture thresholds

●

Sensing integrity counter

●

Atrial Lead Position Check results

1

The time in AT/AF is calculated from the point of AT/AF Onset. For more information, see Section 5.1, “AT/AF
detection”, page 124.

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You can access device and lead performance data from several different screens on the
programmer:

●

Quick Look II screen: Data > Quick Look II

●

Battery and Lead Measurements screen: Data > Device/Lead Diagnostics > Battery and
Lead Measurements > [Open Data]

●

Lead Trends screen: Data > Device/Lead Diagnostics > Lead Impedance Trends >
[Open Data]

3.10.1 Remaining Longevity estimate and replacement indicators

The device automatically measures the battery voltage several times a day. At 24:00, the
device calculates the automatic daily battery voltage by averaging the measurements taken
during the previous 24 hours. The device uses this data to evaluate the battery status and to
calculate a Remaining Longevity estimate. This estimate is based on automatic daily battery
voltage measurements, time since implant, programmed parameter settings, and device
recorded events, as applied to a statistical analysis of accelerated battery discharge data.

Note: The Remaining Longevity estimate is updated when parameters are reprogrammed
and when the device is interrogated.

The calculation of the Remaining Longevity estimate provides maximum, minimum, and
mean values for the amount of time remaining until the device reaches the Recommended
Replacement Time (RRT). The mean value is reported as the Remaining Longevity
estimate. The maximum and minimum remaining longevity estimates are 95th percentile
values calculated from the distribution of this data. That is, approximately 95% of devices are
expected to reach RRT before the reported maximum value, and approximately 95% of
devices are expected to reach RRT after the reported minimum value. When scheduling the
replacement of the device, do not use the estimate of remaining longevity. Instead, schedule
the device replacement after the RRT condition is reached.

The device reaches RRT when 3 consecutive automatic daily battery voltage
measurements are less than or equal to the RRT voltage. After this occurs, the programmer
displays the RRT symbol and the date when the battery reached RRT. Also, the programmer
displays “Replace Device” instead of the Remaining Longevity estimate. If the programmer
displays the RRT symbol, contact your Medtronic representative and schedule a
replacement procedure with your patient. The expected service life of the device after RRT,
defined as the Prolonged Service Period (PSP), is 6 months (180 days).

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After the first 90 days of the PSP have passed, the device reaches the Elective Replacement
Indicator (ERI) and the programmer displays the ERI symbol.2 When the device reaches
ERI, it automatically changes the pacing mode to VVI and sets the pacing rate to 65 bpm. It
also sets AT/AF Detection to Monitor and disables the following features:

●

Rate Hysteresis

●

Ventricular Rate Stabilization

●

Sleep

●

Pre-arrhythmia EGM

After the 180-day PSP has expired, the device reaches End of Service (EOS), and the
programmer displays the EOS symbol.

2

Warning: Replace the device immediately if the programmer displays an EOS indicator. The
device may lose the ability to pace, sense, and deliver therapy adequately after the EOS
indicator appears.

Note: After ERI, all pacing parameters can be programmed, including mode and rate.
Reprogramming the pacing parameters may reduce the duration of the ERI to EOS period.

3.10.2 Lead impedance measurements

Every day at 03:00, the device automatically measures the lead impedance for each lead
polarity on each implanted lead using subthreshold electrical pulses. These pulses are
synchronized to sensed or paced events and do not capture the heart.

The daily automatic lead impedance measurements are displayed on the Lead Trends
screen, which plots the data as a graph. The graph displays up to 15 of the most recent
measurements and up to 60 weekly summary measurements (showing minimum,
maximum, and average values for each week). Significant or sudden changes in lead
impedance may indicate a problem with the lead.

If the device is unable to perform automatic lead impedance measurements, gaps are
present in the trend graph.

If Lead Monitor detects a possible lead system failure, a Lead Warning annotation appears
on the impedance trend graph for the affected lead. For more information, see Section 4.4,
“Lead Monitor”, page 64.

2

ERI may be indicated before the end of 90 days, and EOS may be indicated before the end of 180 days if the
actual battery usage exceeds the expected conditions during the PSP. Refer to the device manual for more
information about expected conditions during the PSP.

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Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

3.10.3 Sensing amplitude measurements

Every day at 02:15, the device begins to measure the amplitude of intrinsic sensed events.
The device attempts to measure the amplitude of 9 normal intrinsic sensed events, and then
records the median value from those events. If the device has not collected 9 amplitude
measurements by 24:00, no measurement is recorded. The sensing amplitude trend graph
shows a gap for that day.

The daily automatic sensing amplitude measurements are displayed on the Lead Trends
screen, which plots the data as a graph. The graph displays up to 15 of the most recent
measurements and up to 60 weekly summary measurements (showing minimum,
maximum, and average values for each week). Significant or sudden changes in sensing
amplitude may indicate a problem with a lead.

3.10.4 Capture threshold measurements

If the Capture Management feature is programmed to Adaptive or Monitor, the device
automatically performs daily pacing threshold searches and records the results in the
capture threshold trends data. For more information, see Section 4.7, “Capture
Management”, page 77.

The results of the daily pacing threshold measurements are displayed on the Lead Trends
screen in the Capture Threshold trend graph. The graph displays up to 15 of the most recent
measurements and up to 60 weekly summary measurements, showing minimum,
maximum, and average values for each week.

The Lead Trends screen also displays programmed values for pacing output and Capture
Management parameters, the last measured threshold value, and a link to a detailed view of
the last 15 days of threshold measurement data. The details screen shows daily results from
the last 15 days of threshold measurements. These results include the dates, times,
threshold measurements, pacing amplitude values, and notes describing the results of each
pacing threshold search.

The capture threshold trend data provides a way to evaluate Capture Management
operation and the appropriateness of the current pacing output values. In addition, sudden
or significant changes in pacing threshold may indicate a problem with a lead.

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3.10.5 Sensing Integrity Counter

When the device senses high-frequency electrical noise, the result is often a large number
of ventricular sensed events with intervals near the programmed value for ventricular
blanking after a ventricular sense (V. Blank Post VS). The Sensing Integrity Counter records
the number of ventricular events with intervals that are within 20 ms of the V. Blank Post VS
parameter value. A large number of short ventricular intervals may indicate oversensing,
lead fracture, or a loose setscrew. If the Sensing Integrity Counter reports more than 300
short ventricular intervals, investigate potential sensing and lead integrity issues.

3.10.6 Atrial Lead Position Check results

The device can be programmed to automatically disable atrial tachyarrhythmia therapies if
the daily Atrial Lead Position Check identifies a potential problem with the lead position. The
Battery and Lead Measurements screen displays the result of the most recent Atrial Lead
Position Check. For more information, see Section 6.1, “Atrial therapy scheduling”,
page 134.

3.11 Automatic device status monitoring

The device automatically and continuously monitors internal conditions that affect device
operation and require attention. If any such conditions occur, a device status indicator is
recorded in memory, and a device status indicator warning is displayed on the programmer
screen when the device is interrogated. Device status indicator warnings are displayed on
the programmer screen and are reported as Quick Look II Observations.

Caution: Inform your Medtronic representative if a device status indicator warning is
reported as a Quick Look II Observation or is displayed on the programmer screen after
interrogating a device.

For more information about responding to device status indicator warnings, refer to the
programming guide.

3.11.1 Operation of automatic device status monitoring

The device monitors and records device status indicators for the following conditions:

●

Device reset

●

Serious device memory failure

●

AT/AF therapies disabled

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3.11.1.1 Device reset

A device reset is a safety feature that can automatically change parameter values or clear
diagnostic data in response to a problem with device memory. A device reset may occur
when the device is exposed to extreme conditions, such as cold temperatures (before
implant), electrocautery, external defibrillation, or intense, direct x-ray exposure.

There are two types of device reset: partial and full. A partial reset clears some or all of the
diagnostic data, but the programmed parameters are not affected. A full reset clears all
diagnostic data and changes programmed parameters to default reset values. These
parameters provide basic device functionality (VVI pacing at 65 bpm) and are considered
safe for the majority of patients. For more information about the default reset values for a
device model, refer to the parameter tables in the device manual for that model.

The device records a device status indicator when a device reset occurs that requires
attention. The device status indicator warning describes how data was affected by the reset.
Read the message accompanying the indicator and follow the screen instructions carefully.

3.11.1.2 Serious device memory failure

In rare cases, a disruption of the device memory can occur from which the device cannot
recover. If this happens, a device status indicator is recorded, and device parameters are
reset to values that provide basic functionality (VVI pacing at 65 bpm). After a serious device
memory failure, wireless communication is disabled, and device programming is not
operational. Immediate replacement of the device is recommended.

3.11.1.3 AT/AF therapies disabled

The device can record a device status indicator and automatically disable atrial
tachyarrhythmia therapies if any of the following situations occur:

●

A ventricular episode was detected following delivery of an automatic atrial therapy prior
to either redetection of AT/AF or termination of AT/AF. Atrial therapy is disabled if it
appears that an atrial therapy has initiated a ventricular arrhythmia.

●

The Atrial Lead Position Check failed.

●

The device detected an accelerated ventricular rate during ATP therapy.

For more information about disabling atrial therapies, see Section 6.1, “Atrial therapy
scheduling”, page 134.

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4 Pacing features

4.1 Sensing

The device must sense the occurrence of intrinsic cardiac events while avoiding oversensing
so that it can deliver therapies appropriately. Effective sensing can reduce the effects of long
depolarizations after paced events, oversensing the same event, cross-chamber sensing,
sensing far-field R-waves, sensing T-waves, noise, and interference.

Effective sensing is essential for the safe and effective use of the device. The device senses
in both the atrium and right ventricle using the sensing electrodes of the leads implanted in
those chambers. You can adjust the sensitivity to intracardiac signals. Each sensitivity
setting represents a threshold value that defines the minimum electrical amplitude
recognized by the device as a sensed event in the atrium or right ventricle.

Note: Selecting a higher value for the sensing threshold reduces the sensitivity to lower
amplitude signals.

Programmable blanking periods and refractory periods help to screen out extraneous
sensing or to prevent the device from responding to it. Both blanking periods and refractory
periods follow pacing pulses and sensed events. Sensing is inhibited during blanking
periods. The device is able to sense events that occur during refractory periods, but it marks
them as refractory events. Refractory events generally have no effect on the timing of
subsequent pacing events, but they are used by the tachyarrhythmia detection features.

The device provides both bipolar and unipolar sensing polarities, and sensing operates
differently depending on the polarity.

4.1.1 Operation of sensing thresholds with bipolar sensing

For leads that are configured as bipolar, the device automatically adjusts the sensing
thresholds after certain paced and sensed events to help reduce the oversensing of
T-waves, cross-chamber events, and pacing. Each threshold adjustment depends on the
type of event that precedes the adjustment. During an automatic adjustment, the sensing
threshold automatically increases, but it gradually decreases toward the programmed
sensitivity value, which is the minimum amplitude that can be sensed. The threshold
decrease is intended to be rapid enough to allow subsequent low-amplitude signals to be
sensed. Threshold adjustment corresponding to both leads configured for bipolar sensing
(and nominal settings) is shown in Figure 5.

Reference Manual 43

AS

AS

VS

VS

VP

AP

A. Sense EGM

V. Sense EGM

Sensing threshold

Marker Channel

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 5. Adjustment of sensing thresholds with bipolar sensing

1 After an atrial sensed event, the device is temporarily less sensitive to atrial events.
2 After a ventricular sensed event, the device is temporarily less sensitive to ventricular events.
3 After an atrial paced event, the device is temporarily less sensitive to ventricular events, but the

sensitivity to atrial events remains the same.
4 After a ventricular paced event, the device is temporarily less sensitive to atrial events.
5 After the post-pace blanking period, the device is temporarily less sensitive to ventricular events.

Note: When high-amplitude sensed events occur, the decrease in sensitivity is limited to
prevent undersensing of subsequent intrinsic events.

4.1.2 Operation of sensing thresholds with unipolar sensing

The device does not adjust the sensing threshold for a lead that is configured for unipolar
sensing. The sensing threshold remains at the level determined by the programmed
sensitivity parameter. The fixed thresholds corresponding to both leads configured for
unipolar sensing are shown in Figure 6.

44 Reference Manual

A. Sense EGM

V. Sense EGM

Sensing threshold

Marker Channel

AS

VS VS VP

ASAP

Atrial blanking

Ventricular

blanking

Marker Channel

A
S

A

P

V
P

V
S

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 6. Fixed sensing thresholds with unipolar sensing

4.1.3 Operation of blanking periods

Blanking periods follow paced and sensed events. Blanking periods help to prevent the
device from sensing pacing pulses, post-pacing depolarization, T-waves, and oversensing
of the same event. The blanking periods after paced events are longer than or equal to those
after sensed events to avoid sensing the atrial and ventricular depolarizations.

Programmable parameters determine the lengths of the blanking periods that follow sensed
events and paced events.

Figure 7. Programmable blanking periods

1 For the duration of this atrial blanking period, which is defined by the A. Blank Post AS parameter,

atrial sensing is disabled after a sensed atrial event.
2 For the duration of this ventricular blanking period, which is defined by the V. Blank Post VS

parameter, ventricular sensing is disabled after a sensed ventricular event.

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3 For the duration of this atrial blanking period, which is defined by the A. Blank Post AP parameter,

atrial sensing is disabled after a paced atrial event.
4 For the duration of this ventricular blanking period, which is defined by the V. Blank Post VP

parameter, ventricular sensing is disabled after a paced ventricular event.

The cross-chamber blanking periods listed in Table 6 are nonprogrammable.

Table 6. Cross-chamber blanking periods

Parameter Value

Atrial blanking after a ventricular pacing pulse (bipolar atrial sens­ing)

Atrial blanking after a ventricular pacing pulse (unipolar atrial sens­ing)

Ventricular blanking after an atrial pacing pulse (bipolar ventricular
sensing)

Ventricular blanking after an atrial pacing pulse (unipolar ventricu­lar sensing)

a

If the RV pacing amplitude is programmed at 8 V, this value is 35 ms.

30 ms

40 ms

30 ms

40 ms

a

4.1.4 Operation of Post-Ventricular Atrial Blanking (PVAB)

The system uses Post-Ventricular Atrial Blanking (PVAB) to eliminate the effect of far-field
R-waves. Far-field R-waves are ventricular events that are sensed in the atrium. The PVAB
operation is determined by 2 programmable parameters: PVAB Interval and PVAB Method.
Atrial events that are sensed during the PVAB interval are used only by tachyarrhythmia
detection and do not affect pacing timing. However, changing the PVAB interval determines
whether or not events fall in the interval.

The 3 programmable values of PVAB Method are Partial, Partial+, and Absolute. This
parameter determines whether atrial events that occur during PVAB interval are sensed by
the device.

4.1.4.1 PVAB operation with bipolar atrial sensing

Partial PVAB – When the Partial PVAB method is used, atrial events sensed during the

programmed PVAB interval are not used by the bradycardia pacing features but are used by
the tachyarrhythmia detection features.

Partial+ PVAB – The Partial+ PVAB method may eliminate the sensing of far-field R-waves
more effectively than Partial PVAB. The Partial+ PVAB method operates similarly to the
Partial PVAB method. The difference is that after a ventricular event, the atrial sensing
threshold is increased for the duration of the programmed PVAB interval. During this time,
far-field R-waves are less likely to be sensed. After the PVAB interval, the atrial sensing
threshold gradually returns to the programmed level. Extending the PVAB interval may affect

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AS

AS

AS

Ab

VS

VS

VS

Marker Channel

PVAB Interval

Marker Channel

Marker Channel

A. Sense EGM

A. Sense EGM

Sensing threshold

A. Sense EGM

Partial PVAB

Partial+ PVAB

Absolute PVAB

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

intrinsic and far-field R-wave sensing because it changes the time during which the sensing
threshold is increased.

Absolute PVAB – When the Absolute PVAB method is used, no atrial events are sensed in
the PVAB interval. The Absolute PVAB method is recommended only for addressing
complications that are not addressed by the other PVAB methods.

Warning: Programming Absolute as the PVAB Method means that no atrial sensing occurs
during the blanking interval. Absolute blanking may reduce the ability to sense AT/AF and
reduce the ability to discriminate between VT and SVT. Use the Partial or Partial+ methods
unless you are sure that Absolute blanking is appropriate.

Figure 8. Comparison of the PVAB methods

1 When the Partial PVAB method is used, if the far-field R-wave exceeds the atrial threshold, an Ab

marker indicates that the event is sensed during the PVAB interval.
2 With the Partial+ PVAB method, after a ventricular sensed or paced event, the atrial sensing

threshold increases, and the device is less sensitive to atrial events.

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AS

AS

Ab

VS

VS

Marker Channel

PVAB Interval

Marker Channel

A. Sense EGM

Sensing threshold

A. Sense EGM

Partial PVAB or Partial+
PVAB

Absolute PVAB

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

3 When the Absolute PVAB method is used, an atrial event is blanked in the PVAB interval whether

or not the far-field R-wave exceeds the atrial threshold.
4 Except for the change in the atrial sensing threshold, the Partial+ PVAB and Partial PVAB

methods are similar. With either method, atrial events sensed in the PVAB interval are used by the

tachyarrhythmia detection features.

4.1.4.2 PVAB operation with unipolar atrial sensing

Partial PVAB and Partial+ PVAB – If the atrial lead is configured for unipolar sensing, Partial

PVAB and Partial+ PVAB operate in the same way. Atrial sensed events in the PVAB interval
are not used by bradycardia pacing features but are used by tachyarrhythmia detection
features.

Absolute PVAB – When the Absolute PVAB method is used, no atrial events are sensed in
the PVAB interval. The Absolute PVAB method is recommended only for addressing
complications that are not addressed by the other PVAB methods.

Warning: Programming Absolute as the PVAB Method means that no atrial sensing occurs
during the blanking interval. Absolute blanking may reduce the ability to sense AT/AF and
reduce the ability to discriminate between VT and SVT. Use the Partial or Partial+ methods
unless you are sure that Absolute blanking is appropriate.

Figure 9. Comparison of PVAB methods (unipolar atrial sensing)

1 When the Partial PVAB method is used, if the far-field R-wave exceeds the atrial threshold, an Ab

marker indicates that the event is sensed during the PVAB interval.
2 When the Absolute PVAB method is used, an atrial event is blanked in the PVAB interval whether

or not the far-field R-wave exceeds the atrial threshold.

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Marker Channel

Fixed PVARP

PVAB

A
P

A
P

V
P

V
P

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.1.5 Operation of refractory periods

During a refractory period, the device senses normally but classifies sensed events as
refractory and limits its response to these events. The pacing refractory periods prevent
inappropriately sensed signals, such as far-field R-waves or electrical noise, from triggering
certain pacing timing intervals. Pacing refractory periods do not affect tachyarrhythmia
detection.

The availability of refractory periods depends on the programmed pacing mode. The Post
Ventricular Atrial Refractory Period (PVARP) is available in dual chamber pacing modes, and
the Atrial Refractory Period is available in atrial pacing modes.

4.1.5.1 Post Ventricular Atrial Refractory Period (PVARP)

The Post Ventricular Atrial Refractory Period (PVARP) follows a paced, sensed, or refractory
sensed ventricular event. An atrial event that is sensed during this interval is classified as a
refractory event. It does not inhibit a scheduled atrial pace or start a Sensed AV interval. The
PVARP setting is only programmable for dual chamber pacing modes (except DOO mode).

●

When the device is operating in the DDDR and DDD modes, the PVARP setting prevents
the tracking of retrograde P-waves that could initiate a pacemaker-mediated
tachycardia.

●

When the device is operating in the DDIR and DDI modes, the PVARP setting prevents
the inhibition of atrial pacing based on sensed retrograde P-waves. PVARP should be
programmed to a value longer than the VA interval (retrograde) conduction time.

Figure 10. Timing for fixed PVARP

The PVARP parameter may be programmed to Auto instead of a fixed value. Auto PVARP
adjusts PVARP in response to changes in the patient’s intrinsic rate or pacing rate. During a
Mode Switch episode, the device enables Auto PVARP. For more information, see
Section 4.9, “Auto PVARP”, page 89.

The PVARP setting may be extended by the PVC Response feature or the PMT Intervention
feature.

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4.1.5.2 Atrial Refractory Period

The Atrial Refractory Period setting is programmable only for the AAI and AAIR single
chamber pacing modes. The Atrial Refractory Period prevents the inhibition of atrial pacing
due to sensed far-field R-waves or noise.

4.1.6 Programming sensing

Table 7. How to navigate to sensing parameters

Parameters Path

Atrial Sensitivity
RV Sensitivity
A. Refractory

Atrial Sense Polarity
RV Sense Polarity

PVARP Params > PVARP…

PVAB Interval
PVAB Method

A. Blank Post AP
A. Blank Post AS

V. Blank Post VP
V. Blank Post VS

Params

Params > Sense Polarity…

Params > Blanking…

Sensing thresholds – The sensing thresholds, set by programming the sensitivity
parameters, apply to all features related to sensing, including detection, bradycardia pacing,
and the Sensing Test.

Bradycardia pacing and sensing – A combination of high pacing pulse width or high
amplitude with a low sensing threshold may cause oversensing across chambers or in the
same chamber. Programming a lower pulse width, lower amplitude, longer pace blanking, or
a higher sensing threshold may eliminate this inappropriate sensing.

High ventricular sensing threshold – If the RV Sensitivity value is set too high, the device
may undersense. This may result in asynchronous pacing.

Long blanking periods – If you set the blanking periods too long, the device may
undersense.

Dual chamber sensing and bradycardia pacing modes – The device senses in both the
atrium and the ventricle at all times, except when the programmed bradycardia pacing mode
is DOO, VOO, or AOO. When the pacing mode is programmed to DOO or VOO, there is no
sensing in the ventricle. When the pacing mode is programmed to DOO or AOO, there is no
sensing in the atrium.

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High atrial sensing threshold – If you set the Atrial Sensitivity value too high, the device
may not provide reliable sensing of P-waves during AT/AF episodes and sinus rhythm.

Atrial pacing and ventricular sensing – If you program the device to an atrial pacing
mode, make sure that it does not sense atrial pacing pulses as ventricular events.

Atrial lead selection – Atrial leads with narrow tip-to-ring spacing (for example, 10 mm) may
reduce far-field R-wave sensing.

Repositioning the atrial lead – You may need to reposition or replace the atrial sensing
lead if reprogramming the Atrial Sensitivity parameter does not provide reliable atrial sensing
during AT/AF episodes and sinus rhythm.

Absolute PVAB – PVAB Method cannot be set to Absolute when the programmed pacing
mode is ODO, AAI, or AAIR.

Upper rates and refractory periods – A combination of high Upper Sensor Rate, high
Upper Tracking Rate, and a long refractory period may result in competitive atrial pacing. For
more information, see Section 4.13, “Non-Competitive Atrial Pacing”, page 99.

Low sensing threshold with bipolar sensing – If you set a sensitivity parameter to its
most sensitive value, the device is more susceptible to electromagnetic interference (EMI),
cross-chamber sensing, and oversensing.

Low sensing threshold with unipolar sensing – The device is more susceptible to
electromagnetic interference (EMI) and oversensing.

Recommended ventricular sensing threshold with bipolar sensing – Setting RV
Sensitivity to 0.9 mV is recommended to limit the possibility of oversensing and
cross-chamber sensing.

Recommended ventricular sensing threshold with unipolar sensing – Setting RV
Sensitivity to 2.8 mV is recommended to limit the possibility of oversensing.

Recommended atrial sensing threshold with bipolar sensing – Setting Atrial
Sensitivity to 0.3 mV is recommended to optimize the effectiveness of atrial detection and
pacing operations while limiting the possibility of oversensing and cross-chamber sensing.

Recommended atrial sensing threshold with unipolar sensing – Setting
Atrial Sensitivity to 0.45 mV is recommended to limit the possibility of oversensing.

Testing sensitivity after reprogramming – If you change the ventricular sensing threshold
or the ventricular sensing polarity, evaluate for proper sensing.

Effects of myopotential sensing in unipolar sensing configurations – In unipolar
sensing configurations, the device may not distinguish myopotentials from cardiac signals.
This may result in a loss of pacing due to inhibition. Also, unipolar atrial sensing in atrial
tracking modes can result in elevated ventricular pacing rates. To address these situations,
the device may be programmed to be less sensitive (using higher sensitivity values).
However, the sensitivity level must be balanced against the potential to undersense true

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cardiac signals. Typically, this balance is easily attained for ventricular sensing using
sensitivity values around 2.8 mV, but it may be difficult to attain for atrial sensing because of
the smaller P-wave amplitudes.

Atrial Rate Stabilization (ARS) and unipolar sensing – ARS must be Off if the atrial
sensing polarity is unipolar or if Lead Monitor is set to Adaptive for the atrial lead.

AT/AF Detection and unipolar pacing or sensing – AT/AF Detection must be set to
Monitor if the atrial sensing polarity is unipolar, if the atrial pacing polarity is unipolar, or if
Lead Monitor is set to Adaptive for the atrial lead. Mode Switch remains available.

Atrial Capture Management (ACM) operation and unipolar sensing – If the atrial
sensing polarity is unipolar and Atrial Sensitivity is less than 0.45 mV, the ACM feature does
not operate.

Disabling Atrial Sensitivity – When changing the mode to VVI or VVIR, consider
programming Atrial Sensitivity to Off. Disabling Atrial Sensitivity can preserve battery energy
and avoid collection of irrelevant data.

Note: When Atrial Sensitivity is programmed to Off, AT/AF monitoring is disabled.

4.1.7 Evaluation of sensing

4.1.7.1 Using the Sensing Test to evaluate sensing

The Sensing Test allows you to measure P-wave and R-wave amplitudes. These
measurements may be useful for assessing lead integrity and sensing performance. After
the Sensing Test is complete, the test results are displayed on the test screen. You may view
and print the results when desired. For more information, see the programming guide.

4.1.7.2 Viewing the Sensing Integrity Counter

To access the Sensing Integrity Counter, select the Remaining Longevity [>>] button from
the Quick Look II screen, or select Data > Device/Lead Diagnostics > Battery and Lead
Measurements > [Open Data].

The Sensing Integrity Counter records the number of short ventricular intervals that occur
between patient sessions. A large number of short ventricular intervals may indicate
oversensing, lead fracture, or a loose setscrew. If the Sensing Integrity Counter reports more
than 300 short ventricular intervals, investigate potential sensing and lead integrity issues.

Note: If the number of short intervals that are displayed exceeds 300, the programmer
displays a Quick Look II observation.

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4.1.7.3 Viewing P-wave and R-wave amplitude trends

To access P-wave and R-wave amplitude trends, select the [>>] button next to Wave
Amplitude on the Quick Look II screen, or select Data > Device/Lead Diagnostics > P/R
Wave Amplitude Trends > [Open Data].

P-wave and R-wave amplitude trend data may be useful for assessing lead integrity and
sensing performance.

4.2 Basic pacing

Patients have a variety of conditions for which pacing therapy may be indicated. These
conditions include cardiac asystole, chronic AT/AF, loss of atrioventricular (AV) synchrony, or
poor ventricular function due to heart failure.

Dual chamber and single chamber pacing modes address different cardiac conditions. Dual
chamber pacing restores AV synchrony by sensing and stimulating 2 chambers of the heart,
the right atrium and right ventricle. Single chamber pacing supports patients with infrequent
or no occurrences of asystole or patients with chronic AT/AF and for whom dual chamber
pacing is not justified.

4.2.1 Operation of pacing and sensing

The output energy for pacing pulses in each chamber is determined by individually
programmed amplitude and pulse width parameters. Although you can program these
parameters manually, the Capture Management feature is available to manage pacing
output energies in the atrium and right ventricle. For more information, refer to Section 4.7,
“Capture Management”, page 77.

The device provides sensing in both the atrium and right ventricle. Refer to Section 4.1,
“Sensing”, page 43 for information about sensing thresholds, sensing polarity, blanking
periods, and refractory periods.

4.2.2 Operation of dual chamber pacing

In dual chamber modes, pacing and sensing occur in the atrium and ventricle. The dual
chamber pacing modes include DDDR, DDD, DDIR, and DDI. In the DDD mode, pacing
occurs at the programmed Lower Rate in the absence of intrinsic atrial activity. In the DDI
mode, pacing occurs at the programmed Lower Rate. In the DDDR and DDIR modes, which
are rate-responsive, pacing occurs at the sensor rate.

Reference Manual 53

200 ms

PAV PAV SAV PAV PAV

ECG

Marker Channel

AV interval

PVARP

Sensor rate interval

V
P

V
P

V
P

A
P

A
S

A
R

V PV

P

A PA

P

A
P

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.2.2.1 AAIR<=>DDDR and AAI<=>DDD modes

For information about the AAIR<=>DDDR and AAI<=>DDD modes (MVP modes), see
Section 4.5, “Managed Ventricular Pacing (MVP)”, page 66.

4.2.2.2 DDDR and DDD modes

DDDR and DDD are atrial tracking pacing modes. Atrial tracking means that when the device
senses an intrinsic atrial event, it schedules a ventricular paced event in response (see
Figure 11). The delay between the sensed atrial event and the corresponding ventricular
paced event is the Sensed AV (SAV) interval. The delay between the paced atrial event and
the corresponding ventricular paced event is the Paced AV (PAV) interval. If a pacing interval
ends before the device senses an atrial event, the device paces the atrium and then
schedules a ventricular paced event to occur at the end of the PAV interval. If a ventricular
sensed event occurs during the SAV interval or the PAV interval, ventricular pacing is
inhibited. A sensed atrial event that occurs during the Post Ventricular Atrial Refractory
Period (PVARP) is classified as refractory. It does not inhibit atrial pacing, and it is not
tracked. For more information, see Section 4.1.5.1, “Post Ventricular Atrial Refractory Period
(PVARP)”, page 49.

Figure 11. Operation of dual chamber pacing in DDDR

1 An atrial paced event starts a PAV interval.
2 An atrial sensed event starts an SAV interval.
3 An atrial sensed event during PVARP is not tracked.

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200 ms

A
P

A
S

V
P

V
P

A
P

A
P

V
P

V
P

V
P

A
R

PAV PAV PAV

ECG

Marker Channel

AV interval

PVARP

Sensor interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.2.2.3 DDIR and DDI modes

In the DDIR and DDI modes, sensed atrial events are not tracked. When an atrial event is
sensed, atrial pacing is inhibited, but a SAV interval is not started (see Figure 12). Instead,
ventricular pacing is delivered at the current pacing rate (for example, at the Lower Rate or
sensor rate). If the current pacing interval ends before the device senses an atrial event, the
device paces the atrium and then schedules a ventricular paced event to occur at the end of
the PAV interval. If a ventricular sensed event occurs during the PAV interval, ventricular
pacing is inhibited. A sensed atrial event that occurs during PVARP is classified as refractory
and does not inhibit atrial pacing. For more information, see Section 4.1.5.1, “Post
Ventricular Atrial Refractory Period (PVARP)”, page 49.

Figure 12. Operation of dual chamber pacing in DDIR

1 An atrial paced event starts a PAV interval.
2 An atrial sensed event inhibits the scheduled atrial paced event but does not start an SAV interval

(is not tracked).
3 An atrial event that is sensed during PVARP does not inhibit the scheduled atrial paced event.

4.2.2.4 ODO mode (bradycardia pacing off)

The ODO mode does not deliver ventricular or atrial pacing, regardless of the intrinsic rate.
The ODO mode is intended only for those situations in which bradycardia pacing is not
necessary.

Dual chamber sensing, atrial detection, and ATP therapy continue to operate as
programmed when pacing is programmed to the ODO mode.

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Caution: The device provides no pacing support when it is programmed to ODO mode. Use
ODO mode only in clinical situations where bradycardia pacing is not necessary or is
detrimental to the patient.

4.2.2.5 DOO mode

The DOO mode provides AV sequential pacing at the programmed Lower Rate with no
inhibition by intrinsic events.

The device provides no sensing or detection in either chamber when it is programmed to
DOO mode. Use DOO mode only in situations in which asynchronous pacing is warranted.
AT/AF Detection must be programmed to Monitor to program the device to the DOO mode.

4.2.3 Operation of single chamber pacing

Single chamber pacing modes are used to pace either the atrium or the ventricle.

4.2.3.1 AAIR<=>DDDR and AAI<=>DDD modes

For information about the AAIR<=>DDDR and AAI<=>DDD modes (MVP modes), see
Section 4.5, “Managed Ventricular Pacing (MVP)”, page 66.

4.2.3.2 VVIR and VVI modes

In the VVIR and VVI modes, the ventricle is paced if no intrinsic ventricular events are
sensed. Pacing occurs at the programmed Lower Rate in the VVI mode and at the sensor
rate in the VVIR mode (see Figure 13). In VVIR and VVI modes, the device continues sensing
atrial events for tachyarrhythmia detection purposes.

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200 ms

A
S

V
P

V
P

A
S

V PV

S

V
P

ECG

Marker Channel

Sensor interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 13. Operation of single chamber ventricular pacing in VVIR

1 A ventricular paced event occurs when no intrinsic ventricular event is sensed.

4.2.3.3 AAIR and AAI modes

In the AAIR and AAI modes, the atrium is paced if no intrinsic atrial events are sensed. Pacing
occurs at the programmed Lower Rate in the AAI mode and at the sensor rate in the AAIR
mode (see Figure 14).

A sensed event that occurs during the Atrial Refractory Period is classified as refractory and
does not inhibit atrial pacing. In AAIR and AAI modes, the device continues sensing
ventricular events for tachyarrhythmia detection purposes. VT detection is available but
compromised in the AAIR and AAI modes. Cross-chamber blanking can cause ventricular
events to go undetected, and crosstalk can cause false detection.

Warning: Do not use the AAIR or AAI mode in patients with impaired AV nodal conduction
because these modes do not provide ventricular support.

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A PA RA PA

S

A
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V
S

V
S

V
S

V
S

ECG

Marker Channel

Atrial Refractory Period

Sensor rate interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 14. Operation of single chamber atrial pacing in AAIR

1 An atrial event during the Atrial Refractory Period does not restart the A-A pacing interval.

4.2.3.4 VOO mode

The VOO mode provides ventricular pacing at the programmed Lower Rate with no inhibition
by intrinsic ventricular events.

Ventricular detection is not available in the VOO mode, although the device continues to
sense in the atrium and monitor for atrial arrhythmias. AT/AF Detection must be programmed
to Monitor to program the device to the VOO mode.

4.2.3.5 OVO mode (bradycardia pacing off)

The OVO mode does not deliver ventricular pacing, regardless of the intrinsic rate. The OVO
mode is available only in the single-chamber devices. It is intended only for those situations
in which bradycardia pacing is not necessary.

Caution: The device provides no pacing support when it is programmed to OVO mode. Use
OVO mode only in clinical situations where bradycardia pacing is not necessary or is
detrimental to the patient.

4.2.3.6 AOO mode

The AOO mode provides atrial pacing at the programmed Lower Rate with no inhibition by
intrinsic atrial events.

When the device is programmed to the AOO mode, it provides no atrial detection although
it offers ventricular sensing and monitoring. AT/AF Detection must be programmed to
Monitor to program the device to the AOO mode.

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4.2.4 Programming pacing therapies

Table 8. How to navigate to basic pacing parameters

Parameters Path

Mode Params

Lower Rate
Upper Track

Atrial Amplitude
RV Amplitude

Atrial Pulse Width
RV Pulse Width

Paced AV Params > Paced AV…

Sensed AV Params > Sensed AV…

TherapyGuide – It is suggested that you use the TherapyGuide feature to determine the
pacing mode for a particular patient. For more information, refer to the programming guide.

SAV and PAV intervals – The SAV interval is usually programmed 30 ms to 50 ms shorter
than the PAV interval. This is done to compensate for the inherent delay between the actual
cardiac event in the atrium and when it is detected by the device.

Upper Tracking Rate – When programming higher upper tracking rates, SAV and PVARP
should be programmed to appropriate values to assure 1:1 tracking. See Section 4.2.6.

Upper rates and refractory periods – A combination of a high Upper Sensor Rate and a
long refractory period may result in competitive atrial pacing. See Section 4.2.6. Consider
programming Non-Competitive Atrial Pacing (NCAP) to On.

Pacing safety margins – Pacing pulses must be delivered at an adequate safety margin
above the stimulation thresholds.

High pacing output levels – The pulse width and amplitude settings affect the longevity of
the device, particularly if the patient requires bradycardia pacing therapy most of the time.

Cross-chamber sensing – Pulse width and amplitude settings can affect cross-chamber
sensing. If you set the pulse width and amplitude values too high, pacing pulses in one
chamber may be sensed in the other chamber, which could cause inappropriate inhibition of
pacing.

Params > Amplitude…

Params > Pulse Width…

4.2.5 Evaluation of pacing therapies

To verify that the device is pacing appropriately, review the Percentage of Time (% of Time)
data on the Quick Look II screen. Select Data > Quick Look II.

Percentage of Time (% of Time) – For single chamber modes, the % of Time section
reports the patient’s pacing (VP) and sensing (VS) as the percentage of the total time during

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R

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R

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R

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AV interval

PVARP

Lower Rate interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

the reporting period. For dual chamber modes, the % of Time section reports the percentage
of ventricular pacing (VP) and atrial pacing (AP).

For detailed information about viewing and interpreting all of the information available from
the Quick Look II screen, see Section 3.1, “Quick Look II summary data”, page 19.

4.2.6 Tracking rapid atrial rates

When the device is operating in the DDDR or DDD mode, the device can track atrial rhythms
only up to a certain rate. Limitations on atrial tracking include the 2:1 block rate and the
programmed Upper Tracking Rate as described in Section 4.2.6.1.

4.2.6.1 2:1 block

2:1 block occurs when the intrinsic atrial interval is so short that every other atrial sensed
event occurs during PVARP (see Figure 15). These atrial events do not start an SAV interval
and therefore do not result in ventricular paced events. Because only every other atrial
sensed event is tracked, the ventricular pacing rate becomes one-half of the atrial rate. 2:1
block can be a desirable means to prevent rapid ventricular pacing rates at the onset of
AT/AF. However, 2:1 block during exertion or exercise is normally undesirable because the
ventricular pacing rate can suddenly drop to one-half of the atrial rate. The sudden reduction
in cardiac output can result in patient symptoms.

Figure 15. Example of pacing at the 2:1 block rate

1 One of every 2 atrial sensed events occurs during PVARP and is not tracked.

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In some cases, the amount of rate drop is less severe because of pacing at the sensor rate
(in the DDDR mode) or because of various rate stabilization, smoothing, or overdrive pacing
features.

A common method to prevent 2:1 block at elevated exercise rates (for example, above
150 bpm) is to program shorter than nominal values for SAV and PVARP. Use of the Rate
Adaptive AV and Auto PVARP features dynamically shortens the operating SAV and PVARP
values during exercise. For more information, see Section 4.9, “Auto PVARP”, page 89.
These features can prevent symptomatic 2:1 block during exercise while allowing nominal or
longer SAV and PVARP values at resting rates to help prevent rapid ventricular pacing rates
during the onset of AT/AF.

When programming the SAV or PVARP parameters, the programmer calculates and
displays the 2:1 block rate. When the 2:1 block rate is dynamic due to the Rate Adaptive AV
or Auto PVARP features, the programmer displays 2:1 block rates at both rest and exercise.

4.2.6.2 Upper Tracking Rate

The programmable Upper Tracking Rate also places a limit on the fastest ventricular pacing
rate during atrial tracking. Typically, the Upper Tracking Rate is programmed to a rate that is
below the exercise 2:1 block rate. If not, the 2:1 block rate becomes the absolute limit and the
Upper Tracking Rate cannot be achieved.

1:1 atrial tracking can occur for sinus rates at or below the programmed Upper Tracking Rate.
As the sinus rate increases beyond the Upper Tracking Rate, the ventricular pacing rate
remains at the Upper Tracking Rate, and the observed SAV interval (AS-VP interval)
lengthens with each subsequent pacing cycle. Eventually, after several pacing cycles, an
atrial sensed event occurs during PVARP and is not tracked, resulting in a dropped beat. This
pattern repeats itself as long as the sinus rate remains above the programmed Upper
Tracking Rate. The dropped beat occurs less often when the sinus rate is only slightly above
the Upper Tracking Rate (for example, every 7 or 8 beats) and more often as the sinus rate
exceeds the Upper Tracking Rate by larger amounts (for example, every 3 or 4 beats).

This Upper Tracking Rate behavior is known as pacemaker Wenckebach (see Figure 16).
Wenckebach behavior can be further defined by how often the dropped beat occurs,
typically as a ratio of the number of atrial sensed events compared to ventricular paced
events (for example, 8:7, 7:6, 6:5, or 3:2). Further increases in the atrial rate may eventually
reach the 2:1 block rate where the ratio becomes 2:1.

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200 ms

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S

A
R

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S

V PV PV PV

P

A
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A
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S

SAV SAV SAVSAV SAV SAV

ECG

Marker Channel

AV interval

PVARP

Upper Tracking Rate interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 16. Example of Wenckebach pacing

1 SAV intervals extend so that ventricular paced events do not violate the Upper Tracking Rate.
2 An atrial event occurs during PVARP and is not tracked.
3 Tracking resumes on subsequent atrial events.

To provide proper tachyarrhythmia detection, the programmer forces the various
tachyarrhythmia detection rates to be programmed above the programmed Upper Tracking
Rate and prevents long blanking periods from being programmed along with high Upper
Tracking Rate values.

4.3 Implant Detection

Implant Detection is a 30 min period, beginning when the device is placed in the surgical
pocket. During this period, the device verifies lead connection and automatically configures
the pacing and sensing lead polarities. When the Implant Detection period is completed,
various automatic features and diagnostics are activated.

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Implanted

leads

connected

Lead polarity is

confirmed (25

min)

Implant detection

Implant
Detection
complete

Lead polarity is

configured (5

min)

Device/lead revision

Device/lead revision

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.3.1 Operation of Implant Detection

Figure 17. Implant Detection process

When Implant Detection is started, the device performs lead impedance measurements to
verify that the leads have been connected to the device. After the first 5 min of the Implant
Detection process, the device automatically configures the sensing and pacing polarities.
The atrial and RV leads are configured independently. If the device detects high impedance
paces that are out of range, it assumes the lead is not connected due to a lead or device
revision, and it restarts the 30 min Implant Detection process. When lead configuration is
complete, the device configuration is set to bipolar for bipolar leads and to unipolar for
unipolar leads. When Implant Detection is complete, the device activates the following
features:

●

MVP feature

●

Atrial Preference Pacing

●

Rate Response

●

Capture Management feature

●

diagnostic data collection

Lead polarity can also be set manually at any time during the automatic configuration
process.

Note: If unipolar leads are being implanted, consider manual completion of Implant
Detection.

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4.3.2 Programming Implant Detection and lead polarity

Table 9. How to navigate to Implant Detection and lead polarity parameters

Parameters Path

Implant Detection Params > Additional Features…

Atrial Pace Polarity
RV Pace Polarity

Atrial Sense Polarity
RV Sense Polarity

MRI SureScan mode and lead polarity – The MRI SureScan parameter cannot be
programmed to On unless Atrial Pace Polarity and RV Pace Polarity are set to Bipolar.

Implant Detection – If you program Implant Detection to Off/Complete before the 30 min
automatic polarity configuration period is completed, you must program sensing and pacing
polarities manually.

AT/AF Detection – AT/AF Detection must be set to Monitor if the Atrial Pace or Sense
Polarity is set to Unipolar. This prevents the device from delivering atrial ATP therapies in the
unipolar configuration.

Polarity override – Do not override the polarity verification prompt with bipolar polarity when
a unipolar lead is connected. Overriding the polarity verification prompt results in no pacing
output.

Params > Pace Polarity…

Params > Sense Polarity…

4.4 Lead Monitor

The Lead Monitor feature measures lead impedances over the long-term operation of the
device and enables the device to switch bipolar pacing and sensing to unipolar when bipolar
lead integrity is in doubt.

4.4.1 Operation of Lead Monitor

Throughout the life of the device, Lead Monitor measures the impedance of each pacing
pulse to determine whether it falls within the programmed impedance range for a stable lead.
If you program Lead Monitor to Adaptive, the device switches bipolar pacing and sensing
polarity to unipolar when lead integrity is in doubt due to a prevalence of high or low
impedance paces. If you program Lead Monitor to Monitor Only, the device monitors
impedance values to determine whether they are out of range, but it does not switch polarity
when an out-of-range lead impedance is detected.

When a lead polarity switch occurs, the sensitivity value is changed to the nominal unipolar
sensitivity value if the previous value was more sensitive.

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Caution: If the Lead Monitor detects out-of-range lead impedance, the device records a
Quick Look II Observation. In addition, a lead warning message is displayed as a window on
the programmer screen the next time the device is interrogated by a programmer. Investigate
possible lead system failures. Lead system failures can prevent adequate sensing or full
pacing support.

4.4.2 Programming Lead Monitor

Table 10. How to navigate to Lead Monitor parameters

Parameters Path

Atrial Lead Monitor
RV Lead Monitor
Atrial Min Limit
RV Min Limit
Atrial Max Limit
RV Max Limit

MRI SureScan mode and lead polarity – When Lead Monitor switches the polarity to
unipolar, the MRI SureScan parameter cannot be programmed to On.

AT/AF Detection – When the Atrial Lead Monitor is set to Adaptive, AT/AF Detection must
be set to Monitor because there is potential for the device to switch to a unipolar
configuration.

Params > Pace Polarity…

4.4.3 Evaluation of Lead Monitor

If Lead Monitor detects a possible lead system failure, the device records a Quick Look II
Observation. In addition, a lead warning message is displayed as a window on the
programmer screen the next time the device is interrogated by a programmer. Also, the lead
impedance trend data displays a Lead Warning annotation. To access the lead impedance
trend data, select the Impedance [>>] button on the Quick Look II screen.

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AAI(R) DDD(R)

Loss of AV conduction

AV conduction resumes

Intact AV

conduction

AV block

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.5 Managed Ventricular Pacing (MVP)

Unnecessary right ventricular pacing may be associated with an increased risk of atrial
fibrillation, left ventricular dysfunction, and congestive heart failure, especially in patients
with intact or intermittent AV conduction.

The MVP (Managed Ventricular Pacing) feature is an atrial-based pacing mode that is
designed to switch to a dual chamber pacing mode in the presence of AV block. Specifically,
the MVP feature provides the following functions:

●

AAI(R) mode pacing when AV conduction is intact

●

the ability to switch to DDD(R) pacing during AV block

●

periodic conduction checks while operating in DDD(R) mode, with the ability to switch
back to AAI(R) mode when AV conduction resumes

●

backup ventricular support for transient loss of AV conduction

4.5.1 Operation of MVP mode

Figure 18. Overview of MVP mode

3,4,5

4.5.1.1 Intact AV conduction

The MVP modes, AAIR<=>DDDR and AAI<=>DDD, provide AAIR or AAI mode pacing while
monitoring AV conduction. If AV conduction is intact, the device remains in AAIR or AAI
mode. While operating in AAI or AAIR mode, the parameters associated with single chamber
atrial pacing are applicable.

3

Sweeney M, Hellkamp A, Ellenbogen K, et al. Adverse effect of ventricular pacing on heart failure and atrial
fibrillation among patients with normal baseline QRS duration in a clinical trial of pacemaker therapy for sinus
node dysfunction. Circulation. 2003;107:2932-2937.

4

Nielsen J, Kristensen L, Andersen H, et al. A randomized comparison of atrial and dual-chamber pacing in 177
consecutive patients with sick sinus syndrome: echocardiographic and clinical outcome. J Am Coll Cardiol.
2003;42:614-623.

5

Andersen H, Nielsen J, Thomsen P, et al. Long-term follow-up of patients from a randomised trial of atrial versus
ventricular pacing for sick-sinus syndrome. Lancet. 1997;350:1210-1216.

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200 ms

A
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V
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V
S

V
S

V-V intervals

ECG

Marker Channel

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.5.1.2 Loss of AV conduction

If 2 of the 4 most recent A-A intervals are missing a ventricular event, the device identifies a
loss of AV conduction and switches to the DDDR or DDD mode. The device provides backup
ventricular pacing in response to dropped ventricular events until the loss of AV conduction
is identified.

Figure 19. Switching from AAIR mode to DDDR mode

1 The device operates in AAIR mode.
2 At the onset of AV block, the device supplies ventricular backup pacing pulses.
3 The device switches to DDDR mode.

4.5.1.3 AV conduction resumes

After switching to DDDR or DDD mode, the device periodically checks AV conduction for an
opportunity to return to AAIR or AAI mode. The first AV conduction check occurs 1 min after
switching to DDDR or DDD mode. During the conduction check, the device switches to AAIR
or AAI pacing mode for one cycle.

●

●

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If the next A-A interval includes a sensed ventricular beat, the conduction check
succeeds. The device remains in AAIR or AAI pacing mode.

If the next A-A interval does not include a sensed ventricular beat, the conduction check
fails and the device switches back to the DDDR or DDD mode. The time between
conduction checks doubles (2, 4, 8 … min, up to a maximum of 16 hours) with each failed
conduction check.

200 ms

A
P

A
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A
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A
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A
P

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V
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P

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S

V-V intervals

ECG

Marker Channel

200 ms

A
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A
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A
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A
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P

V
P

V
P

V
P

V
P

V-V intervals

ECG

Marker Channel

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 20. Switching from DDDR mode to AAIR mode after AV conduction resumes

1 The device operates in DDDR mode.
2 The device performs an AV conduction check. AV conduction is detected.
3 The device operates in AAIR mode.

4.5.1.4 Complete AV block

For patients with complete AV block, the device operates in DDDR or DDD mode
persistently. Every 16 hours, the device checks for AV conduction, which results in a single
dropped ventricular beat.

Figure 21. Remaining in DDDR mode after an AV conduction check

1 The device operates in DDDR mode.
2 The device checks for AV conduction, but conduction is not detected.
3 The device continues to operate in DDDR mode.

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AAI(R)

DDIRDDD(R)

Normal Sinus, AV Conduction

AV Block AT/AF

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.5.1.5 Transient loss of conduction

For transient loss of AV conduction, the device remains in the AAIR or AAI mode and
provides a backup ventricular pacing pulse in response to an A-A interval that is missing a
ventricular sense.

4.5.1.6 Interactions with MVP mode

Mode Switch – Mode Switch and the MVP modes operate together to adjust the pacing

mode according to the patient’s atrial rhythm and AV conduction status.

Figure 22. Operation of MVP mode and Mode Switch

Atrial Refractory Period – When the MVP feature is operating in AAIR or AAI mode, the

Atrial Refractory Period is not programmable. Instead, it is automatically adjusted according
to the current heart rate: 600 ms for rates below 75 bpm and 75% of the ventricular interval
for rates at or above 75 bpm.

PVCs and ventricular tachyarrhythmias – When the MVP feature is operating in AAIR or
AAI mode, the device inhibits atrial pacing in response to PVCs, PVC runs, and ventricular
tachyarrhythmia episodes. This behavior is intended to prevent unnecessary atrial pacing
when the ventricular rate is faster than the pacing rate. It also allows tachyarrhythmia
detection features to operate without disruption from blanking periods caused by atrial
pacing.

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4.5.2 Programming MVP mode

Table 11. How to navigate to MVP parameters

Parameters Path

Mode Params

Maximum AV Interval Limit Params > Paced AV…

V-V interval variations – Depending on the patient’s intrinsic rhythm and conduction, the
MVP mode allows V-V interval variations and occasional pauses of up to twice the lower rate
interval.

Paced AV and Sensed AV – For MVP modes, it is not necessary to program longer Paced
AV and Sensed AV intervals to promote intrinsic AV conduction. Paced AV and Sensed AV
intervals apply only when loss of AV conduction is detected.

Lower rate programming – Upon abrupt loss of AV conduction, prior to switching to DDDR
or DDD mode, ventricular pacing support can be as low as one-half the programmed Lower
Rate for 2 consecutive intervals. For patients with sinus bradycardia or frequent loss of AV
conduction, program the Lower Rate to 50 bpm or higher.

Complete heart block – For patients with complete heart block, the device drops 1 beat
every 16 hours (AV conduction check). See Section 4.5.1.4. If this is undesirable, permanent
DDDR or DDD modes may be more appropriate.

Long PR intervals – For patients with long PR intervals, the device remains in the AAIR or
AAI mode. Permanent DDDR or DDD modes may be more appropriate for patients with
symptomatic first-degree AV block. Alternatively, you can program the Maximum AV Interval
Limit parameter, which causes the device to switch to DDDR or DDD mode if the patient’s PR
interval exceeds the programmed limit.

Operation immediately after implant – The device is shipped in the MVP mode, initially
operating in DDD mode. Approximately 30 min after implant, the device checks for AV
conduction and switches to AAIR or AAI mode if the next A-A interval includes a sensed
ventricular beat. See Section 4.5.1.3 for more information.

4.5.3 Evaluation of MVP mode

The following features can help to assess atrial and ventricular pacing and MVP
performance:

●

the pacing mode indicator near the top of the programmer screen

●

the Quick Look II screen

●

the Rate Histograms diagnostic and report

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●

the Cardiac Compass Trends diagnostic and report

●

the MVP Mode Switches diagnostic and MVP Mode Switches List report

4.5.3.1 Pacing mode indicator

When the device is programmed to an MVP mode, the pacing mode indicator near the top
of the screen displays the mode in which the device is currently operating. (When the device
is operating in an atrial mode, the pacing mode indicator displays AAI+ or AAIR+.)

4.5.3.2 Quick Look II screen

To access the Quick Look II screen, select Data > Quick Look II.

The Quick Look II screen shows the percentages of atrial and ventricular pacing since the
last session. The Quick Look II screen also indicates whether the device is programmed to
an MVP mode. If the present programmed pacing mode is AAIR<=>DDDR or AAI<=>DDD,
the message “MVP On” appears on the Quick Look II screen. Otherwise, the screen displays
“MVP Off.”

For detailed information about viewing and interpreting all of the information available from
the Quick Look II screen, see Section 3.1, “Quick Look II summary data”, page 19.

4.5.3.3 Cardiac Compass Trends

To access Cardiac Compass Trends, select the Cardiac Compass [>>] button on the Quick
Look II screen, or select Data > Clinical Diagnostics > Cardiac Compass Trends >
[Open Data].

The % Pacing/day trend in Cardiac Compass Trends provides a view of pacing over time that
can help you identify pacing changes and trends. The graph displays the percentage of all
events occurring during each day that are atrial paces and ventricular paces. This
information can help determine the effect of MVP mode on ventricular pacing.

4.5.3.4 MVP Mode Switches diagnostic

To access the MVP Mode Switches diagnostic, select Data > Clinical Diagnostics > MVP
Mode Switches > [Open Data].

The MVP Mode Switches diagnostic lists up to 10 of the most recent MVP mode switches to
DDD(R). For more information, see Section 3.8, “MVP Mode Switches data”, page 35

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Activity sensor

Acceleration/

Deceleration

Pacing rate

Rate Profile

Optimization

Rate calculation

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.6 Rate Response

Some patients exhibit heart rates that do not adapt to changes in their physical activity. Their
symptoms might be shortness of breath, fatigue, or dizziness. This includes patients with
chronotropic incompetence and patients with chronic or paroxysmal AF.

Rate-responsive pacing adapts the pacing rate to changes in patients’ physical activity. This
device uses an activity sensor to measure the patient’s movement and to determine the
appropriate pacing rate. It provides dual-slope rate response that may be either automatic or
manual.

4.6.1 Operation of Rate Response

Figure 23. Overview of Rate Response

The Rate Response system includes an activity sensor to measure patient movement, rate
calculation to convert the patient’s level of physical activity to a pacing rate, Rate Profile
Optimization to automatically adjust rate response settings over time, and acceleration and
deceleration to smooth the pacing rate. This pacing rate is also described as the sensor rate.

4.6.1.1 Activity sensing

The activity sensor is an accelerometer in the device that detects the patient’s body
movements. Because activity detection varies from patient to patient, the sensitivity to
motion can be adjusted by reprogramming the Activity Threshold parameter. If the Activity
Threshold is lowered, smaller body movements influence the pacing rate. If the Activity
Threshold is raised, body movements must be larger to influence the pacing rate. The
activity count used to calculate the sensor rate is weighted based on the frequency and
amplitude of the accelerometer signal.

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Upper Sensor Rate

ADL Rate

Exertion rate

range

ADL rate

range

ADL Setpoint

UR Setpoint

Lower Rate

Increasing activity

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

The pacing rate is determined by the patient’s level of physical activity and the rate response
parameters. In the absence of activity, such as when the patient is sitting, the pacing rate is
close to the programmed Lower Rate setting. During increased activity, such as when the
patient is walking, the pacing rate is higher.

4.6.1.2 Rate calculation

The rate curve shows how the device calculates the pacing rate as the patient’s activity level
changes.

Figure 24. Rate curve

Programmable rates – The Lower Rate is the slowest rate at which pacing occurs in the

absence of physical activity. The Activities of Daily Living Rate (ADL Rate) is the approximate
pacing rate during moderate exercise and provides a plateau which helps maintain a stable
pacing rate during changes in moderate activity. The Upper Sensor Rate is the upper limit for
the pacing rate during vigorous exercise.

Rate Response setpoints – The setpoints define the 2 slopes characteristic of dual-slope
Rate Response. The ADL Setpoint determines the weighted activity counts that cause the
pacing rate to reach the ADL Rate. The UR Setpoint determines the weighted activity counts
that cause the pacing rate to reach the Upper Sensor Rate. A lower setpoint means fewer
activity counts are required to reach upper rates.

Automatic Rate Response – With automatic Rate Response, Rate Profile Optimization
continues to adjust the rate curve by varying these setpoints. The rate curve is adjusted
based on how the ADL Response and Exertion Response parameters are programmed. The

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ADL Response controls the first slope, which determines how aggressively the pacing rate
increases from the Lower Rate to the ADL Rate. The Exertion Response controls the second
slope, which determines how aggressively the pacing rate approaches the Upper Sensor
Rate.

Manual Rate Response (Rate Profile Optimization programmed to Off) – With manual
Rate Response, the rate curve is established during a patient session when the rates and
setpoints are programmed. The rate curve remains constant until the parameters are
reprogrammed.

4.6.1.3 Rate Profile Optimization

Rate Profile Optimization automatically adjusts the patient’s rate response between office
visits. The goal of Rate Profile Optimization is to ensure that the rate response remains
appropriate for the full range of patient activities. Each day, the device collects and stores
daily and long-term averages of the percentage of time that the patient sensor-indicated rate
is at different pacing rates. The device then uses the ADL Response and Exertion Response
parameters to define the percentage of time that the pacing rate stays in the ADL rate range
and exertion rate range, respectively. Based on daily comparisons, the device adjusts the
ADL Setpoint, the UR Setpoint, or both setpoints.

By programming new settings for rates or Rate Profile Optimization, you are affecting the
comparisons. Immediate changes occur. These changes project how rate response should
change in the future based on stored sensor rate information and the selected Rate Profile
Optimization settings. The device continues to adjust the rate response over time.

The device adapts Rate Response more rapidly for the first 10 days after Rate Profile
Optimization is first activated post-implant or after certain Rate Response parameters are
manually reprogrammed (Lower Rate, ADL Rate, Upper Sensor Rate, ADL Response, or
Exertion Response). The intent is to quickly match Rate Response to the operation
prescribed by the parameter changes.

Note: Because the device is automatically changing the setpoint values, if you manually
program the setpoint values, Rate Profile Optimization is disabled.

4.6.1.4 Activity Acceleration and Activity Deceleration

The Activity Acceleration and Activity Deceleration parameters are used to smooth the
pacing rate. Activity Acceleration controls how rapidly the pacing rate increases. Activity
Deceleration controls how rapidly the pacing rate decreases and has both fixed values and
the Exercise option. The Exercise setting adjusts the deceleration dynamically based on the
intensity and duration of exercise, and it can extend the deceleration up to 20 min.

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2 4 6 8 10 12 14 16 18 20 22 24

Upper Sensor

Rate

Rate curve: nominal Acceleration and Exercise
Deceleration

Time (min)

Rate curves: alternate Acceleration and Deceleration
values

Lower Rate

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

As shown in Figure 25, changing the values of the Activity Acceleration and Activity
Deceleration parameters affects the pacing rate during and after exertion.

Figure 25. Activity Acceleration and Deceleration curves for rate response

1 Pacing occurs with the patient at rest.
2 Activity increases and Activity Acceleration begins.
3 Activity Acceleration continues toward a higher pacing rate.
4 Pacing occurs at a higher rate during exertion.
5 Exertion ends and the pacing rate decelerates.

4.6.1.5 Rate Response during implant

Rate Response does not operate during an implant procedure to avoid increased pacing
caused by handling. Rate Response and Rate Profile Optimization begin operating when
Implant Detection is complete. For more information, see Section 4.3, “Implant Detection”,
page 62

4.6.1.6 Rate Response parameters screen

The parameters screen for Rate Response shows the rate curve corresponding to the
interrogated parameter values. If you select pending values for the parameters, the screen
also shows a pending curve. The pending curve reflects the immediate changes that will
occur after reprogramming.

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4.6.2 Programming Rate Response

Table 12. How to navigate to Rate Response parameters

Parameters Path

Lower Rate
ADL Rate
Upper Sensor
Rate Profile Optimization
ADL Response
Exertion Response

Activity Threshold
Activity Acceleration
Activity Deceleration
ADL Setpoint
UR Setpoint

TherapyGuide – The TherapyGuide feature suggests parameter values based on
information entered about the patient’s clinical conditions. Parameter values for Rate
Response are included. For more information about the TherapyGuide feature, refer to the
programming guide.

Rate-responsive pacing and DDD or AAI<=>DDD mode – When the programmed
pacing mode is DDD or AAI<=>DDD (an MVP mode) and Mode Switch is enabled, the Rate
Response parameters are programmable. However, these parameters apply only during
Mode Switch episodes when the operating mode is DDIR.

Adjusting the Activity Threshold – For many patients there is no need to reprogram the
Activity Threshold parameter. However, if a patient has minimal rate response during
exercise, the Activity Threshold may need to be programmed to a lower (more sensitive)
setting. The most sensitive setting is “Low”. Conversely, if a patient has an elevated pacing
rate at rest, the Activity Threshold may need to be programmed to a higher (less sensitive)
setting. The least sensitive setting is “High”.

Adjusting Rate Profile Optimization – Before programming other Rate Response
parameters, first verify that the settings for Lower Rate, ADL Rate, and Upper Sensor Rate
are appropriate for the patient.

It may be necessary to reprogram the ADL Response and Exertion Response parameters if
reprogramming the rates does not have the desired effect on Rate Profile Optimization. By
reprogramming the ADL Response and Exertion Response parameters, you can prescribe
a rate profile that matches the patient’s lifestyle or activity levels in each rate range.

Adjust the ADL Response to prescribe how quickly the patient reaches the ADL Rate and the
Exertion Response to prescribe how quickly the patient reaches the Upper Sensor Rate. In
both cases, a lower value decreases the rate responsiveness and a higher value increases
the rate responsiveness.

Params > Rate Response…

Params > Rate Response… > Additional Param­eters…

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Note: If increasing the Exertion Response setting does not make Rate Response aggressive
enough, increase the ADL Response setting.

Adjusting the setpoints manually – You can program Rate Profile Optimization to Off and
program the setpoints manually. In this case, the ADL Setpoint and UR Setpoint determine
the pacing rate curve, and rate response calculations continue to operate as programmed.

4.6.3 Evaluation of Rate Response

4.6.3.1 Rate Histograms

To access Rate Histograms, select Data > Clinical Diagnostics > Rate Histograms >
[Open Data].

Rate Histograms provide information about how Rate Response has been performing since
the previous patient session. For example, if Rate Response was programmed to be more
aggressive, the histograms will likely show that the percentage of atrial pacing has shifted
from lower rates to higher rates.

4.6.3.2 Flashback Memory

Flashback Memory provides a rate trend based on the initial interrogation.

To access Flashback Memory data, select Data > Clinical Diagnostics.

Set the plot display to Rate to see how Rate Response was operating before the patient
session.

Note: To evaluate new Rate Response settings, instruct the patient to complete a hall walk
and then reinterrogate the device.

4.7 Capture Management

Maintaining adequate safety margins for pacing output energies and optimizing device
longevity are critical to patient care. As the patient’s condition changes, pacing thresholds
may change, requiring pacing outputs to be monitored regularly and modified, if necessary,
to capture the myocardium.

The Capture Management feature automatically manages pacing thresholds in the right
atrium and right ventricle. It monitors whether pacing pulses capture the myocardium and,
optionally, adjusts their amplitude to changing patient conditions.

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4.7.1 Operation of the Capture Management feature

The Capture Management feature is a programmable feature that is available for the right
atrium (ACM) and right ventricle (RVCM). In Capture Management operation, the device
prepares for a pacing threshold search, conducts the pacing threshold search, and
determines the pacing threshold. Over time, the threshold measurements are collected to
create threshold trends. If the Capture Management feature is programmed to Adaptive, the
device may automatically adjust the pacing outputs. If the Capture Management feature is
programmed to Monitor, no adjustments occur.

4.7.1.1 Manual adjustment of pacing outputs

You have the option to program pacing outputs manually instead of using the automatic
Capture Management feature. The pacing safety margins should be checked if the Capture
Management feature is programmed to Monitor. Threshold data that is collected during
pacing threshold searches can make it easier for you to select values for pacing output
parameters. For more information, see Section 4.2, “Basic pacing”, page 53.

4.7.1.2 Pacing thresholds and safety margins

The amplitude and pulse width parameters control the output energy of pacing pulses in
each chamber. The pacing output energy determines whether pacing pulses capture the
myocardium. It is necessary for pacing output settings to exceed the pacing threshold by a
safety margin. Pacing threshold variations may be caused by exercise, eating, sleeping,
drug therapy, or changes in other cardiac conditions.

4.7.2 Operation of the Atrial Capture Management feature

The Atrial Capture Management (ACM) feature is available when the pacing mode is
programmed to DDDR, DDD, or an MVP mode (AAIR<=>DDDR or AAI<=>DDD), and it
functions when the device is operating in one of these modes. If ACM is programmed to
Monitor or Adaptive, the device conducts a pacing threshold search to determine the atrial
pacing threshold. If ACM is programmed to Adaptive, the device uses the atrial pacing
threshold to define a target amplitude and adjusts the pacing amplitude toward the target
amplitude. The target amplitude is based on the programmed settings for the Atrial
Amplitude Safety Margin and the Atrial Minimum Adapted Amplitude parameters.

Note: In the event of partial or complete lead dislodgment, ACM may not prevent loss of
capture.

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4.7.2.1 Preparing for an atrial pacing threshold search

Every day at 01:00, the device schedules Capture Management operations in the available
chambers. ACM is scheduled when no other pending features have a higher priority. ACM
starts with a device check to determine if any parameter settings would prevent a search. For
example, the permanent programmed values of Atrial Amplitude or Atrial Pulse Width cannot
exceed limits of 5 V or 1 ms. If the device check is unsuccessful, no atrial pacing threshold
searches are scheduled until the following day.

The device also evaluates whether the patient’s current rhythm is stable enough to support
a pacing threshold search. If the stability check is successful, the pacing threshold search is
initiated. If stability checks are unsuccessful, the device automatically continues to schedule
searches at 30 min intervals until the end of the day. If the device is unable to complete a
stability check successfully during one day, the process is repeated on the following day.

If the programmed pacing mode is an MVP mode and the stability check is successful, the
device switches to a temporary mode for the duration of the pacing threshold search. It
switches from AAIR<=>DDDR mode to DDDR mode or from AAI<=>DDD mode to DDD
mode.

4.7.2.2 Searching for and determining the atrial pacing threshold

The device conducts a pacing threshold search to determine the atrial pacing amplitude
threshold at a fixed pulse width of 0.4 ms. ACM varies the amplitude of test paces to find the
lowest amplitude that consistently captures the atrial myocardium.

If the right atrium responds to a test pace, the result is “Capture”. If no response is detected,
the result is “Loss of capture”. The result of a test pace is ignored if the device cannot
determine whether the test pace captures the myocardium. In this case, testing may
continue with additional test paces at the same test amplitude. If there are too many
inconclusive results, the device stops the pacing threshold search and retries it at the next
scheduled period. See Section 4.7.2.4.

A pacing threshold search begins at a test amplitude that is 0.125 V lower than the last
measured threshold. If there was no previous search, a new search begins at 0.75 V. The
device continues to decrease the test amplitude in steps of 0.125 V until a test amplitude is
classified as being below the pacing threshold. The device then increases the test amplitude
in steps of 0.125 V until the same test amplitude is classified as being above the pacing
threshold 3 times in succession. This test amplitude is the atrial pacing threshold.

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AS AS AS AS

AS

AS AS AS AS

Test
AP

AS

VS
or

VP
Test
AP

Capture

Loss of Capture

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

VS
or
VP

AR

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

At the beginning of a pacing threshold search, the device selects a method for evaluating
atrial capture based on the patient’s current sinus rhythm. The Atrial Chamber Reset (ACR)
method is used when the patient has a stable sinus rhythm (a sensed atrial rate that is not
faster than 87 bpm). The AV Conduction (AVC) method is used when stable 1:1 AV
conduction is observed with atrial pacing. These methods evaluate capture differently, but
threshold determination is the same.

Atrial Chamber Reset (ACR) method – In the ACR method, each test pace is preceded by
3 support cycles and followed by 2 extra support cycles. The 3 support cycles monitor AS-AS
intervals to ensure that the patient’s rhythm is stable before the test pace is delivered. The
2 extra support cycles provide time after the test pace for the atrial rhythm to stabilize. ACR
evaluates capture based on the response of the intrinsic rhythm to the atrial test pace. “Loss
of capture” is characterized by an atrial event that follows the test pace but occurs within the
atrial refractory period. As shown in Figure 26, this event is indicated by an AR marker.

Figure 26. Atrial Chamber Reset test method

AV Conduction (AVC) method – In the AVC method, each test pace is preceded by

3 support cycles and followed by a backup pace. During this pacing sequence, overdrive
pacing is accomplished with a faster atrial pacing rate and a lengthened AV interval. These
changes result in a stable AP-VS rhythm with a shorter AP-AP interval. The AP-AP interval
before the test pace is even shorter than the intervals that precede it. The backup pace has
the programmed amplitude and a 1.0 ms pulse width.

The AVC method evaluates capture by observing the conducted ventricular response to an
atrial test pace. The intervals containing the test pace and the support cycle preceding it are
shown in Figure 27. If the test pace captures the atrium, the next VS event results from AV
conduction of the test pace. If no capture occurs, the next VS event results from AV
conduction of the backup pace, which is delivered 70 ms after the test pace.

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Overdrive rate short interval

Overdrive rate shorter

interval

Loss of Capture

Capture

(Expected VS
from Test AP)

(Expected VS from
Backup AP)

Scheduled

VP

70 ms

AP AP

VS VS

VP

Backup AP

Backup AP

Test AP

Test AP

AP-VS

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 27. AV Conduction test method

4.7.2.3 Adjusting atrial pacing outputs

If ACM is programmed to Adaptive, the device automatically adjusts the Atrial Amplitude
based on the pacing threshold search results. After a successful pacing threshold search,
the device calculates a target amplitude by multiplying the programmed Atrial Amplitude
Safety Margin by the amplitude threshold measured at a pulse width of 0.4 ms. The device
calculation for the target amplitude is rounded up to the next programmable amplitude
setting. For information about target amplitudes and safety margins, see Section 4.7.1.2.

Adjustments during the acute phase – The programmable acute phase corresponds to
the lead maturation period. During this time, adequate pacing output is ensured by restricting
output adjustments. The acute phase begins when implant detection is complete. The
nominal length of the acute phase is 120 days, but the Acute Phase Remaining parameter
can be reprogrammed to change the length of the acute phase.

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During the acute phase, the lower limit for Atrial Amplitude is the last user-programmed
amplitude setting or 3.5 V, whichever value is higher. The Atrial Pulse Width is maintained at
the last highest setting programmed by the user or 0.4 ms, whichever value is higher.

Adjustments after the acute phase – The device applies the programmed Atrial
Amplitude Safety Margin to the target amplitude measured at a 0.4 ms pulse width to
determine the new amplitude setting. The device then adjusts the current Atrial Amplitude
toward this target. The device reduces the amplitude by 0.25 V every other day until it
reaches the target amplitude. If the operating amplitude is below the target, the device
adjusts it to the target immediately. The lower limit is set by the programmed Atrial Minimum
Adapted Amplitude. If the operating pulse width has a value different from 0.4 ms, the device
adjusts it to that value.

Upper limit for adjustments – The device adjusts the Atrial Amplitude to 5.0 V and the
Atrial Pulse Width to 1.0 ms if the amplitude threshold is greater than 2.5 V or the target
amplitude is greater than 5.0 V.

4.7.2.4 Stopping an atrial pacing threshold search in progress

The device stops a pacing threshold search immediately if there are sudden changes in the
patient’s heart rate or if other device features take precedence over the search.

When a pacing threshold search cannot be completed, the device automatically schedules
another search within 30 min. If 5 more search attempts are stopped during a day, the pacing
threshold test is suspended until the following day. Whenever this happens, a device check
occurs again, and the process is repeated. The reasons for stopping a pacing threshold
search are noted in the Capture Threshold trends diagnostic. See Section 4.7.5.

4.7.3 Operation of the Right Ventricular Capture Management feature

The Right Ventricular Capture Management (RVCM) feature is available when the pacing
mode is programmed to DDDR, DDD, DDIR, DDI, VVIR, VVI, or an MVP mode
(AAIR<=>DDDR or AAI<=>DDD), and it functions when the device is operating in one of
these modes. If RVCM is programmed to Monitor or Adaptive, the device conducts a pacing
threshold search to determine the RV pacing threshold. If RVCM is programmed to Adaptive,
the device uses the RV pacing threshold to define a target amplitude and adjusts the pacing
amplitude toward the target amplitude. The target amplitude is based on the programmed
settings for the RV Amplitude Safety Margin and the RV Minimum Adapted Amplitude
parameters.

Note: In the event of partial or complete lead dislodgment, RVCM may not prevent loss of
capture.

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Note: If the battery reaches the Elective Replacement Indicator (ERI), the device aborts
RVCM. No additional RV pacing threshold searches are conducted.

4.7.3.1 Preparing for an RV pacing threshold search

Every day at 01:00, the device schedules Capture Management operations in the available
chambers. RVCM is scheduled when no other pending features have a higher priority. RVCM
starts with a device check to determine if any parameter settings would prevent a search. For
example, the permanent programmed values of RV Amplitude or RV Pulse Width cannot
exceed limits of 5 V or 1 ms. If the device check is unsuccessful, no RV pacing threshold
searches are scheduled until the following day.

The device also evaluates whether the patient’s current rhythm is stable enough to support
a pacing threshold search. If the stability check is successful, the pacing threshold search is
initiated. If stability checks are unsuccessful, the device automatically continues to schedule
searches at 30 min intervals until the end of the day. If the device is unable to complete a
stability check successfully during one day, the process is repeated on the following day.

If the programmed pacing mode is an MVP mode and the stability check is successful, the
device switches to a temporary mode for the duration of the pacing threshold search. It
switches from AAIR<=>DDDR mode to DDDR mode or from AAI<=>DDD mode to DDD
mode.

4.7.3.2 Searching for and determining the RV pacing threshold

The device conducts a pacing threshold search to determine the RV pacing amplitude
threshold at a fixed pulse width of 0.4 ms. RVCM varies the amplitude of test paces to find the
lowest amplitude that consistently captures the right ventricular myocardium. The device
evaluates capture by detecting the evoked response signal following each test pace.

If the right ventricle responds to a test pace, the result is “Capture”. If no response is
detected, the result is “Loss of capture”. The result of a test pace is ignored if the device
cannot determine whether the test pace captures the myocardium. In this case, testing may
continue with additional test paces at the same test amplitude. If there are too many
inconclusive results, the device stops the pacing threshold search and retries it at the next
scheduled period. See Section 4.7.3.4.

A pacing threshold search begins at a test amplitude that is 0.125 V lower than the last
measured threshold. If there was no previous search, a new search begins at 0.75 V. The
device continues to decrease the test amplitude in steps of 0.125 V until a test amplitude is
classified as being below the pacing threshold. The device then increases the test amplitude
in steps of 0.125 V until the same test amplitude is classified as being above the pacing
threshold 3 times in succession. This test amplitude is the RV pacing threshold.

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S = Support cycle

T = Test pace

B = Backup pace

S S S T

B

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

In each threshold measurement, the test pace is part of a test sequence (see Figure 28). In
each test sequence, 3 support cycles precede the test pace, and an automatic backup pace
follows the test pace. The support cycles provide pacing at the programmed amplitude and
pulse width. The support cycles may or may not include ventricular paced events. During
testing, the backup pace maintains rhythm stability, and it provides pacing support to the
patient when the test pace does not capture the myocardium. The backup pace is delivered
100 ms after the test pace at the programmed amplitude and a 1.0 ms pulse width.

Figure 28. RVCM test sequence

During a pacing threshold search, the device promotes ventricular pacing, which may affect
the normal pacing operation. To ensure ventricular pacing, the device may adapt timing in
both tracking and nontracking modes.

4.7.3.3 Adjusting the RV pacing outputs

If RVCM is programmed to Adaptive, the device automatically adjusts the RV Amplitude
based on the pacing threshold search results. After a successful pacing threshold search,
the device calculates a target amplitude by multiplying the programmed RV Amplitude
Safety Margin by the amplitude threshold measured at a pulse width of 0.4 ms. The device
calculation for the target amplitude is rounded up to the next programmable amplitude
setting. See Section 4.7.1.2.

Adjustments during the acute phase – The programmable acute phase corresponds to
the lead maturation period. During this time, adequate pacing output is ensured by allowing
only increasing adjustments of the RV Amplitude. The acute phase begins when implant
detection is complete. The nominal length of the acute phase is 120 days, but the Acute
Phase Remaining parameter can be reprogrammed to change the length of the acute phase.

During the acute phase, the lower limit for RV Amplitude is the last user-programmed
amplitude setting or 3.5 V, whichever value is higher. The RV Pulse Width is maintained at the
last highest setting programmed by the user or 0.4 ms, whichever value is higher.

Adjustments after the acute phase – The device applies the programmed RV Amplitude
Safety Margin to the target amplitude measured at a 0.4 ms pulse width to determine the new
amplitude setting. The device then adjusts the current RV Amplitude toward this target. The
device reduces the amplitude by 0.25 V every other day until it reaches the target amplitude.
If the operating amplitude is below the target, the device adjusts it to the target immediately.

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The lower limit is set by the programmed RV Minimum Adapted Amplitude. If the operating
pulse width has a value different from 0.4 ms, the device adjusts it to that value.

Upper limit for adjustments – The device adjusts the RV Amplitude to 5.0 V and the RV
Pulse Width to 1.0 ms if the amplitude threshold is greater than 2.5 V or the target amplitude
is greater than 5.0 V.

4.7.3.4 Stopping an RV pacing threshold search in progress

The device stops a pacing threshold search immediately if there are sudden changes in the
patient’s heart rate or if other device features take precedence over the search.

When a pacing threshold search cannot be completed, the device automatically schedules
another search within 30 min. If 5 more search attempts are stopped during a day, the pacing
threshold test is suspended until the following day. Whenever this happens, a device check
occurs again, and the process is repeated. The reasons for stopping a pacing threshold
search are noted in the Capture Threshold trends diagnostic. See Section 4.7.5.

4.7.4 Programming the Capture Management feature

Warning: The Capture Management feature does not program right ventricular or atrial

outputs above 5.0 V or 1.0 ms. If the patient needs a pacing output higher than 5.0 V or

1.0 ms, you must program Amplitude and Pulse Width manually.

Caution: Epicardial leads have not been determined appropriate for use with RVCM
operation. Program this feature to Off if implanting an epicardial lead.

For information about programming amplitude and pulse width parameters manually, see
Section 4.2, “Basic pacing”, page 53.

Note: An Adaptive symbol next to the value of an Amplitude or Pulse Width parameter
indicates that the programmed value can be adapted by the device. The symbol does not
necessarily indicate that the parameter value has been adapted.

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Table 13. How to navigate to Capture Management parameters

Parameters Path

Atrial Capture Management
Atrial Amplitude
Atrial Amplitude Safety Margin
Atrial Minimum Adapted Amplitude
Atrial Pulse Width
RV Capture Management
RV Amplitude
RV Amplitude Safety Margin
RV Minimum Adapted Amplitude
RV Pulse Width

Atrial Acute Phase Remaining
RV Acute Phase Remaining

Params > Amplitude…

Params > Amplitude… > Additional Parame­ters…

Conditions that may influence threshold measurements – In a small percentage of
patients, the following conditions may influence thresholds measured by RVCM:

●

With poor lead fixation, modulations in pacing timing and rate could influence
thresholds.

●

In rare instances, combinations of morphology and rhythm may result in a low threshold
measurement. This may occur if the pacing threshold search is unable to differentiate
between myocardial contractions caused by the pacing pulse and those caused by
physiologic means.

High threshold measurements with RVCM – In rare instances, the device may not detect
the waveform created by the contracting myocardium immediately following a pacing pulse.
In such instances, a high threshold measurement may result.

Rate Drop Response – The device disables Rate Drop Response during a pacing
threshold search.

4.7.5 Evaluation of the Capture Management feature

4.7.5.1 Quick Look II

To access capture threshold trends and Quick Look II Observations, select Data > Quick
Look II.

Threshold trends – The Quick Look II screen shows trends of average capture thresholds.
The threshold data is collected by the automatic daily threshold tests performed by the
Capture Management feature. Select the Threshold [>>] button to view the Lead Trends and
Capture Threshold diagnostic screens.

For more information about Capture Threshold trends data, see Section 3.10.4, “Capture
threshold measurements”, page 40

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Quick Look II Observations – If there are significant observations about Capture
Management operation, they are shown in the Quick Look II Observations window.

For detailed information about viewing and interpreting all of the information available from
the Quick Look II screen, see Section 3.1, “Quick Look II summary data”, page 19.

4.8 Rate Adaptive AV

A fixed AV interval makes it difficult to select the optimal AV interval value that meets all of the
patient’s needs. A short AV interval is desirable at higher rates to avoid symptomatic 2:1
block during exercise and to avoid asynchronous pacing. A long AV interval is desirable at
lower rates to promote intrinsic AV conduction and to potentially improve hemodynamics.

Rate Adaptive AV shortens AV intervals at elevated rates to maintain 1:1 tracking and AV
synchrony.

4.8.1 Operation of Rate Adaptive AV

Rate Adaptive AV is available when the pacing mode is programmed to DDDR, DDD, DDIR,
DDI, or an MVP mode (AAIR<=>DDDR or AAI<=>DDD). Rate Adaptive AV functions when
the device is operating in the DDDR, DDD, DDIR, or DDI mode.

The way in which Rate Adaptive AV adjusts the operating AV intervals in a linear manner as
the heart rate changes in bpm is shown in Figure 29.

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8060200 100 120 140

80

100

120

140

160

180

40

200

Programmed

PAV

Start Rate Stop Rate

AV Interval

Rate

Programmed

SAV

Minimum
PAV

Minimum
SAV

Rate Adaptive

SAV

Rate Adaptive

PAV

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 29. Operation of Rate Adaptive AV in DDDR mode

The Start Rate determines the heart rate at which the AV intervals begin to shorten. The Stop
Rate determines the heart rate at which the Minimum PAV intervals and Minimum SAV
intervals are applied.

4.8.2 Programming Rate Adaptive AV

Table 14. How to navigate to Rate Adaptive AV parameters

Parameters Path

Rate Adaptive AV
Start Rate
Stop Rate
Minimum Paced AV
Minimum Sensed AV

TherapyGuide – The TherapyGuide feature suggests parameter values based on
information entered about the patient’s clinical conditions. Parameter values for Rate
Adaptive AV are included. For more information about the TherapyGuide feature, refer to the
programming guide.

2:1 block rate programmer message – The programmer calculates the dynamic 2:1 block
rate based on the selected pacing parameters. You can view the calculated dynamic 2:1

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block rate by selecting the information icon. If you select a new value for a parameter that
affects dynamic 2:1 block rate (for example, Sensed AV or PVARP), return to the Parameters
screen and select the information icon to see the recalculated rate.

4.9 Auto PVARP

A fixed value for the Post Ventricular Atrial Refractory Period (PVARP) may not provide the
optimal PVARP setting to meet the changing needs of the patient. At low heart rates, PVARP
should be long enough to prevent pacemaker-mediated tachycardia (PMT). At elevated
heart rates, PVARP should be short enough to avoid 2:1 block and promote AV synchrony.

For more information, see Section 4.1, “Sensing”, page 43 and Section 4.2, “Basic pacing”,
page 53.

Auto PVARP adjusts PVARP in response to changes in the patient’s heart rate or pacing rate.

4.9.1 Operation of Auto PVARP

Auto PVARP is available when the pacing mode is programmed to DDDR, DDD, DDIR, DDI,
or an MVP mode (AAIR<=>DDDR, or AAI<=>DDD). Auto PVARP functions when the device
is operating in the DDDR, DDD, DDIR, or DDI mode.

In a tracking mode (DDDR or DDD), the Auto PVARP feature adjusts PVARP based on the
current heart rate of the patient. When the heart rate is low, PVARP is longer to prevent PMT.
As the heart rate increases, PVARP shortens to maintain 1:1 tracking. Auto PVARP allows
1:1 tracking of atrial events up to 30 bpm above the heart rate or 100 bpm, whichever is
greater.

The programmable Minimum PVARP parameter value sets a limit on the shortest PVARP
that is allowed. If the programmed Minimum PVARP value is reached and the Rate Adaptive
AV (RAAV) parameter is programmed to On, the Sensed AV (SAV) interval is shortened to
help maintain 1:1 tracking.

For more information, see Section 4.8, “Rate Adaptive AV”, page 87.

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Time

1-1 tracking

heart rate

30
min-1
(bpm)

100 min-1

(bpm)

70 min-1

(bpm)

2-1 block

Rate

V

P

V
P

V

P

High pacing

rate

Low pacing

rate

PVAB

PVAB

300 ms

300 ms

V
P

A
P

A
P

A
P

A
P

PVARP

PVARP

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 30. Operation of Auto PVARP in the DDDR or DDD mode

In a nontracking mode (DDIR or DDI), PVARP varies with the current pacing rate to be long
enough to promote AV synchrony at a low pacing rate and short enough to prevent atrial
competitive pacing at a high pacing rate.

The device calculates PVARP to attempt to maintain a 300 ms window of time between the
end of PVARP and the next atrial pace. PVARP is limited to be no shorter than the
programmed interval for the Post-Ventricular Atrial Blanking (PVAB) parameter.

Figure 31. Operation of Auto PVARP in the DDIR or DDI mode

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Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.9.2 Programming Auto PVARP

Table 15. How to navigate to Auto PVARP parameters

Parameters Path

PVARP
Minimum PVARP

Minimum PVARP value selection – When programming a higher value for the Upper
Tracking Rate, you may have to program a lower Minimum PVARP value to achieve 1:1
tracking up to the higher rate. An alternative is to use the Rate Adaptive AV feature, or a
combination of Rate Adaptive AV and a lower Minimum PVARP value. For more information,
see Section 4.8, “Rate Adaptive AV”, page 87.

When you select a new value for Minimum PVARP or Rate Adaptive AV, the programmer
recalculates the dynamic 2:1 block rate at exercise. The device achieves 1:1 tracking up to
the Upper Tracking Rate when the recalculated dynamic 2:1 block rate is above the Upper
Tracking Rate. You can view the programmer message about the dynamic 2:1 block rate by
selecting the information icon on the programmer screen.

Note: The Minimum PVARP parameter only applies when the device is operating in a
tracking mode (DDDR or DDD).

Fixed PVARP with DDI and DDIR modes – If the device is programmed to permanent DDI
mode or DDIR mode, a fixed PVARP may be more appropriate. The purpose of Auto PVARP
in nontracking modes is to support the DDIR portion of Mode Switch operation during AT/AF.

Params > PVARP…

4.10 Rate Drop Response

Patients with carotid sinus syndrome or vasovagal syncope may lose consciousness or
experience related symptoms after significant drops in heart rate. When syncope is caused
primarily by cardioinhibition and when permanent AF is not present, pacing at an elevated
rate may prevent syncope and related symptoms from occurring.

Rate Drop Response monitors the heart for significant drops in heart rate and responds by
pacing the heart at an elevated rate.

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Sinus rate Intervention

Termination

Step - down

Detection

Heart Rate

Time

Sinus rate

Intervention

Duration (2 min)

Step-down

(approx 7 min)

Detection

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.10.1 Operation of Rate Drop Response

Figure 32. Overview of Rate Drop Response

Rate Drop Response operates in phases. During the detection phase, the device monitors
the heart for rate drops that conform to programmed criteria. During the intervention phase,
the device paces the heart at a programmed elevated rate for a programmed duration.
During the step-down phase, the device gradually slows pacing to the sinus rate or the Lower
Rate.

Figure 33. Rate Drop Response Rate and Time

As shown in Figure 33, Rate Drop Response typically operates over several minutes, and
most of this time involves the step-down phase.

Rate Drop Response is available when the pacing mode is programmed to DDD, DDI, or
AAI<=>DDD (MVP mode). Rate Drop Response functions when the device is operating in
the DDD or DDI mode. For the MVP mode, the device operates in DDD mode during Rate
Drop Response interventions. Rate Drop Response does not operate during
tachyarrhythmias, Mode Switch episodes, and Capture Management pacing threshold
searches.

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Detection window: 1

minute

Drop Size: 25 min-1 (bpm)

Intervention Rate: 100 min-1

(bpm)

Drop Rate: 60 min-1 (bpm)

Lower Rate: 45 min-1 (bpm)

Sensed beats

Paced beats

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.10.1.1 Detection

Rate Drop Response provides 2 methods for detecting significant rate drops:

●

Drop Detection

●

Low Rate Detection

Figure 34. Drop Detection

With Drop Detection, the device intervenes when the ventricular rate drops by a specified
number of beats per minute to below a specified heart rate within a specified period of time.
These conditions are established by programming the Drop Size, Drop Rate, and Detection
Window parameters, respectively.

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Intervention Rate:

100 min-1 (bpm)

Lower Rate: 45 min-1

(bpm)

Paced beats

Sensed beats

Detection beats

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 35. Low Rate Detection

With Low Rate Detection, the device intervenes when the atrium is paced at the Lower Rate
for the number of consecutive beats specified by the Detection Beats parameter.

Note: In DDI mode, Low Rate Detection occurs when the atrium or the ventricle is paced at
the Lower Rate for the programmed number of beats.

When both detection methods are programmed, the device intervenes when either Drop
Detection or Low Rate Detection criteria are met. For example, if the heart rate drops too
slowly to meet programmed Drop Detection criteria and continues to drop, the heart is
eventually paced at the Lower Rate. If this continues for the programmed number of
detection beats, the device intervenes.

4.10.1.2 Intervention and step-down

When a rate drop is detected, the device paces the heart at the programmed Intervention
Rate for the programmed Intervention Duration. After the Intervention Duration is complete,
the device reduces the pacing rate by 5 bpm steps per minute. This step-down process
continues until the sinus rate or the Lower Rate is reached.

Intervention pacing and step-down pacing are immediately ended when the device senses
3 consecutive nonrefractory atrial events.

Note: If the Lower Rate is reached at the conclusion of the step-down phase and Low Rate
Detection is programmed, the device does not detect another rate drop until it senses
evidence of a sinus rate that is above the programmed Lower Rate.

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200 ms

EGM

Marker Channel

V
S

V
S

V
S

V
S

V
S

V SV

P

A
P

A PA

P

A
S

A
S

A
S

A
S

V
P

A
P

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

See Figure 36 for an example of the device detecting a rate drop and starting to pace the
heart at the programmed Intervention Rate.

Figure 36. Example of detection and intervention

1 Normal sinus rhythm

3 Intervention pacing started

2 Rate drop detected

4.10.2 Programming Rate Drop Response

Table 16. How to navigate to Rate Drop Response parameters

Parameters Path

Rate Drop Response
Detection Type
Drop Size
Drop Rate
Detection Window
Detection Beats
Intervention Rate
Intervention Duration

TherapyGuide – The TherapyGuide feature suggests parameter values based on
information entered about the patient’s clinical conditions. Parameter values for Rate Drop
Response are included. For more information about the TherapyGuide feature, refer to the
programming guide.

Symptoms during sleep – During sleep, a patient’s sinus rate may fall below the
programmed Lower Rate, thereby triggering intervention pacing at an inappropriate time.
There are two ways to address this problem. First, you can turn off Low Rate Detection.
Second, you can turn on the Sleep feature. The Sleep feature replaces the programmed
Lower Rate with a slower pacing rate during the time of day the patient normally sleeps. For
more information, see Section 4.12, “Sleep feature”, page 97.

Params > Additional Features… > Rate Drop
Response…

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200 ms

V
P

V
P

V
S

V
S

V
P

V
P

A
S

A
S

A
S

A
S

A
S

Lower Rate

interval

ECG

Marker Channel

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Features that adjust pacing rate – Features that adjust the pacing rate, such as the Atrial
Rate Stabilization feature and the Ventricular Rate Stabilization feature, are unavailable
when Rate Drop Response is programmed to On.

4.10.3 Evaluation of Rate Drop Response

The Rate Drop Response Episodes screen provides beat-to-beat data that is useful for
analyzing Rate Drop Response episodes and the events that lead up to them. It also
provides information that may help you select appropriate Rate Drop Response detection
parameters.

To access Rate Drop Response episode data, select Data > Clinical Diagnostics > Rate
Drop Response Episodes > [Open Data].

4.11 Rate Hysteresis

The patient’s intrinsic heart rate is preferable to pacing during extended periods of patient
inactivity, such as when the patient is sleeping.

Rate Hysteresis allows intrinsic rhythms to occur below the programmed Lower Rate.

4.11.1 Operation of Rate Hysteresis

Rate Hysteresis is available when the pacing mode is programmed to VVI or AAI, and it
functions when the device is operating in one of these modes.

Rate Hysteresis allows a slower lower rate when the intrinsic rate is below the programmed
Lower Rate. After each sensed event, the programmed hysteresis rate is applied. After each
paced event, the programmed Lower Rate is applied.

Figure 37. Operation of Rate Hysteresis in VVI mode

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Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

1 The device paces in VVI mode at the programmed Lower Rate.
2 After a ventricular sensed event, the device applies the hysteresis interval (shaded bar).
3 A sensed event occurs before the hysteresis interval expires, so hysteresis operation continues.
4 The hysteresis interval expires, and the device paces the ventricle and reapplies the Lower Rate

interval.

5 The ventricle is paced at the Lower Rate.

4.11.2 Programming Rate Hysteresis

To access Rate Hysteresis, select Params > Additional Features… > Rate Hysteresis.

Verifying adequate cardiac support – The programmed hysteresis rate determines the
slowest heart rate that can occur before pacing starts. Ensure that the selected hysteresis
rate is adequate to support the patient’s cardiac condition.

Programming the hysteresis rate – To avoid large, sudden changes in heart rate, you
would normally select a hysteresis rate that is no more than 30 bpm below the programmed
Lower Rate.

Lower Rate – You cannot program the hysteresis rate to a value equal to or above the Lower
Rate.

Compatibility – Rate Hysteresis cannot be enabled at the same time as Ventricular Rate
Stabilization, Atrial Rate Stabilization, or Atrial Preference Pacing.

4.11.3 Evaluation of Rate Hysteresis

The Ventricular Rate Histogram indicates when the device has allowed the patient’s intrinsic
heart rhythm to prevail at rates lower than the Lower Rate.

To view the Ventricular Rate Histogram, Select Data > Clinical Diagnostics > Rate
Histograms > [Open Data].

4.12 Sleep feature

Some patients have difficulty sleeping when they are paced at a rate that is intended for times
when they are normally awake.

The Sleep feature replaces the programmed Lower Rate with a slower pacing rate during the
time of day that the patient normally sleeps.

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Lower

Rate

Sleep

Rate

Bed time

30 min

30 min

Time

Rate

Wake time

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

4.12.1 Operation of the Sleep feature

Figure 38. Overview of the Sleep feature

The Sleep feature is controlled by 3 programmable parameters: Sleep Rate, Bed Time, and
Wake Time. During the 30 min following the programmed Bed Time, the device gradually
reduces its slowest pacing rate from the Lower Rate to the Sleep Rate. The Sleep Rate
remains in effect until the programmed Wake Time. During the 30 min following the
programmed Wake Time, the device gradually increases its slowest pacing rate from the
Sleep Rate to the Lower Rate.

In rate response modes, when patients awake and become active during programmed sleep
times, the device provides rate-responsive pacing as needed. However, the rate profile
starts from the slower Sleep Rate and increases to the Activities of Daily Living Rate (ADL
Rate). The rate profile above the ADL Rate remains the same.

Programming any bradycardia pacing parameter during the Sleep period cancels the Sleep
operation for that day.

If the patient experiences an AT/AF episode and the Mode Switch feature is operating during
the Sleep period, the device does not pace below the Lower Rate until the AT/AF episode has
ended. For more information, see Section 4.17, “Mode Switch”, page 106.

4.12.2 Programming the Sleep feature

Table 17. How to navigate to Sleep feature parameters

Parameters Path

Sleep
Sleep Rate
Bed Time
Wake Time

Time Zone Params > Data Collection Setup… > Device

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Params > Additional Features… > Sleep…

Date/Time…

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

When you set Bed Time and Wake Time, consider time zone changes resulting from travel,
daylight savings time, and variations in the patient’s sleep patterns, such as variable work
shifts.

4.12.3 Evaluation of the Sleep feature

The Ventricular Rate Histogram shows heart rates below the Lower Rate but above the Sleep
Rate for the percentage of time that correlates to the Sleep period. For more information, see
Section 3.9, “Rate Histograms”, page 36.

Cardiac Compass Trends shows the average ventricular rate during the day and night, which
should indicate that the device is allowing a slower heart rate at night. For more information,
see Section 3.3, “Cardiac Compass Trends”, page 24.

4.13 Non-Competitive Atrial Pacing

An atrial tachycardia may be initiated if an atrial paced event occurs within the vulnerable
period of the atrium. This situation can happen when the device is pacing at a high rate if a
premature atrial contraction occurs during an atrial refractory period and is quickly followed
by an atrial pace.

The Non-Competitive Atrial Pacing (NCAP) feature prevents pacing the atrium too soon after
a refractory atrial sense by delaying the scheduled atrial pace.

4.13.1 Operation of NCAP

NCAP is available when the pacing mode is programmed to DDDR, DDD, DDIR, DDI or an
MVP mode (AAIR<=>DDDR or AAI<=>DDD), and it functions when the device is operating
in one of these modes.

Whenever an atrial refractory sense occurs, the device starts a programmable NCAP
interval. If an atrial pace is scheduled to occur during the NCAP interval, the atrial pace is
delayed until the NCAP interval expires. When an atrial pace is delayed by the NCAP feature,
the AP-VP interval decreases (but not to less than 30 ms). After NCAP decreases the AP-VP
interval, some variation in the VP-VP interval may occur. These variations only affect the
current and next ventricular interval.

The NCAP interval is 400 ms for 1 pacing cycle whenever a PVC Response or a PMT
Intervention occurs.

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200 ms

A
P

A
R

V
P

V
P

V
P

V
P

V
P

V
P

A
P

A
P

A
P

A
P

A
P

ECG

Marker Channel

NCAP interval

AP-VP interval

Medtronic AZURE™ MRI SURESCAN™ / ASTRA™ MRI SURESCAN™

Figure 39. Operation of NCAP

1 The device is pacing at an elevated rate.
2 An atrial refractory sense occurs, starting an NCAP interval (300 ms in this case).
3 After the NCAP interval, the device paces the atrium and then paces the ventricle after a

shortened AP-VP interval.

4.13.2 Programming NCAP

Table 18. How to navigate to NCAP parameters

Parameters Path

Non-Comp Atrial Pacing

Params > Additional Features…

NCAP Interval

4.13.3 Evaluation of NCAP

When evaluating an ECG strip, you will notice that the AP-VP interval has been shortened
and the NCAP interval can be seen as the time between the AR and AP events (see
Figure 39).

4.14 PMT Intervention

In tracking modes (DDDR and DDD), retrograde conduction can result in a
pacemaker-mediated tachycardia (PMT). A PMT is a repetitive sequence in which the
device responds to each retrograde P-wave by pacing the ventricle at an elevated rate,
which, in turn, generates a retrograde P-wave.

The PMT Intervention feature extends the PVARP after detecting a PMT. This interrupts the
PMT by causing the subsequent atrial-sensed event to fall within the refractory period.

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