Medtronic AT501 Reference Guide
AT500™
DDDRP Pacing System
9968 Software
System Reference Guide
Caution: Federal Law (USA) restricts this device to sale by or on the order of a physician.
MEDTRONIC AT500 0
System Reference Guide 0
9968 Software
Model AT501
Model 7253
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.
Antici-Pace, Cardiac Compass, Flashback, Marker Channel, Medtronic, Medtronic
AT500, PatientCheck, PR Logic, QuickLink, Quick Look
Contents
Introduction 9
Abbreviations and Acronyms 10
1 Quick reference 13
Primary Capabilities 14
Physical Characteristics 16
Longevity Expectations 18
Replacement Indicators 19
Magnet Application 19
Measurement Capabilities 19
Telemetry and Diagnostics 20
Emergency Settings 21
Power-On Reset Settings 22
Factory Shipped Settings 23
Emergency VVI Pacing 24
2 Overview 25
System Description 26
Atrial Arrhythmia Prevention 27
Tachyarrhythmia Detection and Monitoring 28
Atrial Tachycardia (AT) Therapy 30
Suspension of Detection and Therapies 31
Disabling of Detection and Therapies 32
3 Sensing and bradycardia pacing 33
Sensing 34
Pacing Mode 40
Bradycardia Pacing Parameters 47
Bradycardia Pacing Operations 49
Mode Switch 55
Rate Responsive Pacing 59
Rate Adaptive AV 64
Ventricular Safety Pacing 68
PVC Response 69
AT500 System Reference Guide
6
Contents
Non-Competitive Atrial Pacing 70
PMT Intervention 74
Atrial Rate Stabilization 76
Atrial Preference Pacing 80
Atrial Lead Position Check 84
4 Tachyarrhythmia detection 87
Atrial Tachyarrhythmia (AT/AF) Detection 88
Non-Programmable Atrial Detection Criteria 96
AT/AF Termination and Redetection 98
Ventricular Monitoring 100
PR Logic Criteria for Ventricular Monitoring 103
5 Tachyarrhythmia therapies 109
Atrial Therapy Availability 110
Atrial ATP Therapy Overview 111
A-Burst+ Pacing 114
A-Ramp Pacing 116
A 50 Hz Burst Pacing (Manual Therapy) 118
Cancelled Atrial Pacing Therapies 118
6 Data collection 121
Data Collection Overview 122
Data Collection Setup 123
Episode and Counter Data 128
Cardiac Compass Trend Data 136
7 Test and follow-up 141
Follow-up Visit Evaluation 142
Beginning a Patient Session 143
Quick Look Monitoring Summary 145
Data Retrieval 151
System Tests 159
EP Study Functions 164
Ending a Patient Session 171
Information for Patients 172
Technical Support 172
AT500 System Reference Guide
A Prescriber’s reference 173
Description 174
Indications 174
Contraindications 175
Warnings and Precautions 176
Bibliography 183
B Implant reference 185
Pre-Implant Information 186
Surgical Approach 187
Testing Leads and Device 188
Connecting Leads and Placing the Device 189
Replacing A Pacemaker with a Medtronic AT500 Device 191
Pre-Discharge Evaluation 192
C Programmer and software reference 193
Programmer/Software Overview 194
Programmer/Software Precautions 195
Connecting the Programmer Hardware 197
Setting Up and Using the Programmer 204
Operating the 9968 Software 209
Live Rhythm Monitor 217
Recording Real-Time Waveforms 226
Printing Reports 230
Save To Disk and Read From Disk Applications 233
Contents
7
D Parameter reference 235
Brady Pacing Parameters 236
Tachy Detection Parameters 239
Antitachy Pacing (ATP) Parameters 240
EP Study Parameters 242
Data Collection Parameters 243
Patient Information Parameter 244
Parameter Restrictions 245
Bradycardia Pacing Programmability 248
Non-Programmable Parameters 250
Notes 252
AT500 System Reference Guide
8
Contents
D Glossary 255
AT500 System Reference Guide
Introduction
Technical Support
9
Introduction
Before implanting the Medtronic AT500 DDDRP pacing system, it
is strongly recommended that the physician:
■ Refer to the product literature packaged with the device for
information about prescribing the Medtronic AT500 system.
■ Thoroughly read this manual, and the technical manuals for
any leads and accessories used with the Medtronic AT500
system.
■ Discuss the procedure and the Medtronic AT500 system with
the patient and any other interested parties, and provide them
with any patient information packaged with the device.
Medtronic encourages physicians to attend an education seminar
on the complete DDDRP pacing system. This includes indications
for use; overview of the Medtronic AT500 system functions;
implant procedure; and patient management.
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 medical
consultation, Medtronic can often refer product users to outside
medical consultants with appropriate expertise.
For more information, contact your local Medtronic representative,
or call or write Medtronic at the appropriate address or telephone
number listed on the back cover.
AT500 System Reference Guide
10
Chapter
Abbreviations and Acronyms
Abbreviations and Acronyms
A- Atrial
AF Atrial Fibrillation
AFDI Atrial Fibrillation Detection Interval (AF Interval parameter)
ANID AT/AF Number of Intervals to Detect (V Beats for Atrial
APP Atrial Preference Pacing
ARP Atrial Refractory Period
ARS Atrial Rate Stabilization
AT Atrial Tachycardia (including atrial flutter)
ATDI Atrial Tachycardia Detection Interval (AT Interval
ATP Antitachycardia Pacing
BOL Beginning of Life
bpm beats per minute
DDDRP dual chamber rate responsive (pacing system) with
ECG Electrocardiogram
EGM Electrogram
EOL End of Life
EPS Electrophysiologic Study
ERI Elective Replacement Indicator
-1
min
mV millivolts
NCAP Non Competitive Atrial Pacing
NID Number of Intervals to Detect
PAC Premature Atrial Contraction
PAV Paced A-V Delay
PMT Pacemaker Mediated Tachycardia
POR Power On Reset
PP P-P interval; an atrial interval
ppm (pacing) pulses per minute
PR P-R interval; an interval between a P-wave and the
Detection parameter)
parameter)
antitachycardia pacing
reciprocal minutes; e.g., pacing pulses per minute
subsequent R-wave
AT500 System Reference Guide
Abbreviations and Acronyms
PVARP Post Ventricular Atrial Refractory Period
PVC Premature Ventricular Contraction
RP R-P interval; an interval between an R-wave and the
subsequent P-wave
RR R-R interval; a ventricular interval
SAV Sensed A-V Delay
SVT Supraventricular Tachycardia
TARP Total Atrial Refractory Period: sum of SAV and PVARP
Vvolts
V- Ventr icular
VT Ventricular Tachycardia
VTDI VT Monitoring Interval (Ventricular Monitoring feature)
11
AT500 System Reference Guide
Primary Capabilities 14
Physical Characteristics 16
Longevity Expectations 18
Replacement Indicators 19
Magnet Application 19
Measurement Capabilities 19
Telemetry and Diagnostics 20
Emergency Settings 21
Power-On Reset Settings 22
Factory Shipped Settings 23
Emergency VVI Pacing 24
Quick reference1
1
14
Chapter 1
Primary Capabilities
Primary Capabilities
Pacing Management
Dual Chamber AT/AF Detection
Dual chamber rate responsive bradycardia pacing in
DDD(R), DDI(R), VVI(R), AAI(R) modes –
Rate Adaptive AV, Ventricular Safety Pacing, PMT Intervention,
Non-Competitive Atrial Pacing
DDIR Mode Switch during paroxysmal atrial episodes
Overdrive DDIR pacing following AT/AF (page 57)
Atrial Rate Stabilization after PACs, to prevent the ‘short-long’
activation sequence (page 76)
Atrial Preference Pacing provides a stable (paced) atrial rhythm
slightly faster than the sinus rate (page 80)
Atrial fibrillation, atrial flutter, and atrial tachycardia detection
with programmable ANID (Number of Intervals to Detect AT/AF)
Dual chamber pattern and rate analysis discriminates far-field
R-wave oversensing and sinus tachycardia from atrial arrhythmias
Atrial Tachycardia Therapy
Up to three automatic AT therapies
A-Burst+ and A-Ramp antitachycardia pacing automatic
therapies
A-50 Hz Burst antitachycardia pacing manual therapy
Automatic daily atrial lead position check helps assure safe
delivery of atrial therapies (page 84)
AT500 System Reference Guide
Patient Management
128 Kbyte data storage includes Flashback™ Memory of A-A
intervals, stored EGMs, Markers, and episode event annotations
Ventricular arrhythmia monitoring – Fixed parameters for
V. High Rate episode recognition; PR Logic™ Pattern and Rate
Analysis recognizes rapidly conducted atrial fibrillation/flutter,
sinus tachycardia, and other 1:1 SVTs
Ambulatory episode confirmation and patient activated event
marking upon request and during detected AT/AF episodes using
hand-held Patient Assistant telemetry device
Long Term Trend reporting of AT/AF prevention, incidence,
symptoms, and therapy efficacy
Tabl e 1-1. Medtronic AT500 Data Collection Summary
Tachy episodes
EGM capacity 140 seconds pre-atrial onset
a
- 35 AT/AF episodes with EGM: text, stored EGM, intervals
- 128 AT/AF episodes without EGM: summary text
- 15 V. High Rate episodes: text, stored EGM, intervals
140 seconds pre-atrial therapy or pre-detection
60 seconds ventricular monitoring
Quick reference
Primary Capabilities
15
EGM sources Four options: atrial / ventricular / AV composites
EGM options - Pre-storage: Store EGM before AT/AF Onset
Flashback Memory 650 A-A intervals before each AT/AF episode where EGM
Counter data AT/AF episodes detected
Patient activated event records 50 recordings outside detected episodes
Histograms -AT/AF Episode Duration
Cardiac Compass Long-term
Trend Data (up to 430 days)
- Detailed Storage option: Store EGM for only treated AT/AF
episodes, or all detected AT/AF episodes
is stored
AT/AF episodes with EGM
Ventricular episodes
Therapies delivered and efficacy
b
timestamp, AT/AF onset status, ventricular cycle length.
-AT/AF Episode Start Time
- Daily AT/AF Episodes: total / treated / terminated
- Daily AT/AF Burden (hours)
- Daily pacing percentages: atrial / prevention / ventricular
- Patient activated events
- Clinician programmed patient management annotations
AT500 System Reference Guide
:
16
Chapter 1
Physical Characteristics
a
All tachy and untreated episode data are stored in the same block of memory.
b
If the patient activates a recording during a detected episode, the episode data annotates the date and time.
Other features
Unique lithium SVO hybrid battery chemistry (page 147)
Medtronic icon-based user interface (page 209)
Full size report printing (page 230)
Two simultaneous real time EGMs: atrial / ventricular / AV
composite
Dual chamber Marker Channel telemetry
Save-to-Disk and Read-from-Disk patient data features
(page 233)
Quick Look programming summary with QuickLink to stored
episodes and observations (page 145)
Non-invasive EP study inductions and manual therapies
Physical Characteristics
Volume 14.1 cc
Mass 26 g
H x W x D 44 mm x 59 mm x 7.5 mm
Radiopaque ID
Materials in
contact with
human tissue
Battery Lithium SVO hybrid (3.1 V nominal)
a
Engineering series number follows the radiopaque code.
AT500 System Reference Guide
a
IJF
Titanium / polyurethane / silicone rubber
Lead Connections
Model AT501 (2) IS-1a (A, V)
a
ISO 5841-3: 1992 (E).
A
IS-1 BIPOLAR
V
IS-1 BIPOLAR
Model AT501
20 ms
Pacing Output
Programmed Pulse Width (0.03 to 1.5 ms)
Recharge
7
Figure 1-1. Lead Connections to Medtronic AT500 Device
Compatible Adaptor Kits
2872 – Medtronic IS-1 bipolar connector bifurcated for dual-site
pacing with two Medtronic IS-1 bipolar pace/sense leads.
Quick reference
Physical Characteristics
17
Output Waveform
5866-24M – Medtronic IS-1 bipolar connector with a Medtronic
5 mm bifurcated bipolar pace/sense lead.
5866-40M – Medtronic IS-1 bipolar connector with a Medtronic
bipolar 3.2 mm low-profile pace/sense lead.
5867-3M – End caps for 5 mm, IS-1, and 3.2 mm low-profile
leads.
AT500 System Reference Guide
18
Chapter 1
Longevity Expectations
Longevity Expectations
The longevity projections are based on the following conditions:
-1
60 ppm (60 min
) pacing rate, pacing mode as indicated, EGM
pre-storage Off. Delivery of atrial antitachycardia pacing therapy
does not appreciably alter the longevity (considered with the
inhibition of atrial pacing during the AT/AF episode).
Tabl e 1- 2. Projected Longevity
Pacing or Sensing Average Longevity
Nominal Outputs – DDDR mode
100% Pacing at 3 V, 0.4 ms (A & V) 5.8 years 6.1 years 7.0 years
50% Pacing at 3 V, 0.4 ms (A & V) 7.1 years 7.3 years 7.9 years
Lower Outputs – DDDR mode
100% Pacing at 2 V, 0.4 ms (A & V) 7.7 years 7.9 years 8.3 years
50% Pacing at 2 V, 0.4 ms (A & V) 8.4 years 8.5 years 8.7 years
Nominal Output – VVIR mode
100% Pacing at 3 V, 0.4 ms (V) 7.2 years 7.4 years 8.0 years
100% Sensing – DDD mode 9.6 years
a
These preliminary longevity projections are based upon accelerated battery
discharge data and device modeling. “Average” refers to the projected mean
longevity of the modeled run of devices at the stated conditions.
a
with pacing impedances of:
500 Ω 600 Ω 1000 Ω
The longevity decreases with: an increase in pacing rate; an
increase in pacing amplitude or pulse width; a decrease in pacing
impedance; a higher ratio of paced to sensed events; or extended
use of the Atrial Preference Pacing, EGM pre-storage, or Holter
Telemetry features. The longevity decreases by approximately
nine days for each month that the EGM pre-storage feature is
enabled.
AT500 System Reference Guide
Replacement Indicators
Battery voltage appears on the programmer display and on
print-outs. See page 146 for more detail on replacement
indicators.
Tab le 1- 3. Battery Voltage Indicators
Elective Replacement (ERI)
Pacing mode and rate (magnet and non-magnet) as programmed
End of Life (EOL) ≤ 2.20 V
Pacing mode and rate (magnet and non-magnet) as programmed
a
The minimum time between ERI and End of Life is four months, assuming 100%
DDD pacing at 60 ppm [60 min
Magnet Application
Tab le 1- 4. Magnet Application
Pacing Mode as programmed
Pacing Rate and Interval as programmed
Quick reference
Replacement Indicators
a
-1
], 3 V, 0.4 ms; and 510 Ω pacing loads.
19
≤ 2.60 V
AT/AF Detection suspended
Ventricular Monitoring suspended
Note: The Medtronic AT500 does not perform a Threshold Margin
Te st .
Measurement Capabilities
Tab le 1- 5. Circuit and Device Measurements
Category Tolerance
Battery voltage ± 4 %
Pacing lead impedance ± 20 % (at implant)
AT500 System Reference Guide
20
Chapter 1
Telemetry and Diagnostics
Telemetry and Diagnostics
Patient diagnostic data collection
■ Counter data
■ Episode data, including stored EGM and Marker Channel,
■ Cardiac Compass trend data, including pacing trends, episode
■ Holter telemetry
Real-Time Telemetry and Waveforms
■ Device status
■ Battery voltage and status
■ Heart rates and intervals: ventricular or A/V tandem
■ EGM: Atrial, Ventricular, and selectable far-field
■ Dual chamber Marker Channel telemetry
■ ECG: Lead I, II, and III
atrial Flashback Memory, and episode data histograms
history, AT/AF burden, and patient activated symptom
annotations
EPS (Electrophysiologic study) function
■ A 50 Hz Burst and A/V PES inductions
■ 50 Hz Burst, Ramp, and Burst+ atrial ATP therapies
System Tests
■ Underlying rhythm
■ Pacing thresholds
■ Pacing lead impedances
AT500 System Reference Guide
Emergency Settings
Instructions for delivering Emergency VVI pacing are given on
page 24.
Tab le 1- 6. Emergency Settings
Parameter Emergency Value
Pacing Mode
Pacing Rate
Pulse Amplitude
Pulse Width
V Sensitivity
A Sensitivity
V Post Sense Blanking
Pace Blanking
Emergency Settings
VVI
70 ppm (70 min
6 V
1.5 ms
As programmed
As programmed
As programmed
200 ms
Quick reference
-1
)
21
AT500 System Reference Guide
22
Chapter 1
Power-On Reset Settings
Power-On Reset Settings
Instructions for restoring Medtronic AT500 system operation after
a reset are given on page 148.
Tabl e 1- 7. Power-On Reset Settings
Parameter Reset Value
Pacing Mode VVI
Pacing Rate 65 ppm (65 min-1)
V. Pulse Width 0.5 ms
V. Amplitude 5 V
V. Sensitivity 0.9 mV
A. Sensitivity 0.3 mV
Pacing Polarity Bipolar (fixed)
Sensing Polarity Bipolar (fixed)
V. Post Sense Blanking 120 ms
Pace Blanking 250 ms
AT / AF Detection Off
AT Therapies Off (all)
Ventricular Monitoring Off
EGM1 Source (stored and on-screen)
EGM2 Source (on-screen)
Holter Telemetry Off
Serial Number RESET
to V
A
Tip
Ring
A
Sense
AT500 System Reference Guide
Factory Shipped Settings
Quick reference
Factory Shipped Settings
23
Tab le 1- 8. Factory Shipped Settings, Model AT501
a
Pacing Mode DDD
Lower Rate / Upper Rate 60 - 120 ppm (60 - 120 min
Mode Switch On
a
PAV / SAV 150 ms / 120 ms
Rate Adaptive AV Off
A and V Pulse Width 0.4 ms
A and V Amplitude 3 V
a
V Sensitivity 0.9 mV
A Sensitivity 0.3 mV
V Post Sense Blanking 120 ms
A Pace Blanking 250 ms
V Pace Blanking 200 ms
Sensing and Pacing Polarity Bipolar (fixed)
PVARP 310 ms
PMT Intervention Off
Non Competitive Atrial Pacing 300 ms
Ventricular Safety Pacing On
a
a
-1
)
Daily Atrial Lead Check Off
Atrial Rate Stabilization Off
Atrial Preference Pacing Off
AT / AF Detection Off
AT Therapies None
Ventricular Monitor Off
EGM1 (stored and on-screen) A
EGM2 (on-screen) A
a
Model 7253 devices are shipped with 4 V pacing amplitudes; Mode Switch,
NCAP, and VSP Off; and EGM1 recorded from A
to A
Tip
Tip
AT500 System Reference Guide
to V
Ring
Ring
, ± 8 mV range
Sense
, ± 16 mV range.
a
24
Fixed
Emergency VVI Pacing
Parameters
Chapter 1
Emergency VVI Pacing
Emergency VVI Pacing
The Medtronic AT500 provides Emergency VVI pacing at the
-1
following settings: 70 ppm (70 min
); Maximum output (6 V,
1.5 ms); Sensitivity as previously programmed; Post sense
blanking as previously programmed; 200 ms pace blanking.
Effect on System Operation – Delivery of Emergency VVI
pacing reprograms the bradycardia pacing parameter values to
those used during emergency pacing (see page 21). Automatic
tachyarrhythmia detection and monitoring are not suspended
during Emergency VVI pacing.
How To Deliver Emergency VVI Pacing
1. Position the programming head over the implanted device.
2. Select [EMERGENCY], or press the red Emergency hard
key. The programmer displays the Emergency VVI Pacing
screen (Figure 1-2).
3. Select [PROGRAM], or press the yellow-on-blue Deliver
hard key. The bradycardia pacing values assume the values
shown on the Emergency VVI Pacing screen.
If programming is not confirmed, verify that the programming head
is properly positioned and select [PROGRAM] or [Retry].
AT500 System Reference Guide
Figure 1-2. Emergency VVI Pacing Screen
System Description 26
Atrial Arrhythmia Prevention 27
Tachyarrhythmia Detection and Monitoring 28
Atrial Tachycardia (AT) Therapy 30
Suspension of Detection and Therapies 31
Disabling of Detection and Therapies 32
Overview2
2
26
Chapter 2
System Description
System Description
The Medtronic AT500 DDDRP pacing system is a
multiprogrammable implantable medical device that monitors,
detects, and treats cardiac dysrhythmias:
■ treatment of bradyarrhythmias including bradycardia and
atrioventricular block
■ detection and treatment of atrial tachycardias (AT) including
atrial flutter (AFl)
■ episode monitoring (without therapy) for atrial fibrillation (AF)
■ episode monitoring (without therapy) for ventricular high rate
episodes such as self-terminating ventricular tachycardia
(VT).
By means of a hand-held telemetry activator, the patient can verify
whether the device has detected a suspected AT/AF episode, and
initiate recording of cardiac event data in the device memory.
The device’s operations are enabled and tailored to the patient’s
needs with a Medtronic programmer, Model 9790/C or
Model 2090, using Medtronic application software, Model 9968.
Model 7253 – Model number 7253 was assigned during the
clinical study to identify Model AT501 devices. Only the nominal
parameter values (page 23) and automatic sensing adjustments
(page 36) are different. The operation and programming of the
devices are identical in every other regard.
Cardiac Interval Measurement – The device measures cardiac
cycle lengths in increments of 10 ms. For event classification and
for calculating interval averages, measurements are truncated to
a 10 ms multiple. (For example, 457 ms is recorded as 450 ms.)
However, output pulses are synchronized by rounding to the
nearest 10 ms. (For example, when a bradycardia pacing interval
for a rate of 70 ppm is computed as 857 ms, the pulse is
scheduled for delivery at 860 ms.)
Lead Configurations – The device requires an appropriate
two-lead system, including bipolar pacing/sensing leads in each
chamber.
AT500 System Reference Guide
Caution: Use of unipolar leads will result in loss of pacing output
Model AT501 (2) IS-1a (A, V)
a
ISO 5841-3: 1992 (E).
A
IS-1 BIPOLAR
V
IS-1 BIPOLAR
Model AT501
and sensing.
Figure 2-1. Lead Connections to Medtronic AT500 Device
Atrial Arrhythmia Prevention
The device provides four features intended to prevent the
incidence of atrial arrhythmias.
Overview
Atrial Arrhythmia Prevention
27
Atrial pacing – A:V sequential and atrial inhibited pacing modes
are available [DDD(R), DDI(R) and AAI(R)]. By maintaining A:V
synchrony, atrial pacing helps to improve hemodynamics.
Atrial Preference Pacing (APP) – Atrial Preference Pacing is a
programmable feature available in DDD(R) and AAI(R) modes to
maintain a stable paced atrial rhythm when the sinus rate exceeds
the lower or sensor rate.
Atrial Rate Stabilization (ARS) – Atrial Rate Stabilization is a
programmable feature available in DDD(R) and AAI(R) modes
designed to reduce the incidence of atrial tachyarrhythmias by
eliminating the long pause that typically follows a premature atrial
contraction (PAC). Such short-long sequences of atrial cycle
lengths have been observed to precede the onset of some
spontaneous atrial tachyarrhythmias.
AT500 System Reference Guide
28
Ventricular Arrhythmia Detected?
Interval and Stability Criteria;
PR Logic Pattern and Rate Analysis
Atrial Tachyarrhythmia Detected?
Atrial Fibrillation (AF)
Atrial Flutter/Tachycardia (AT)
YES
YES
NO
NO
Sustained
AT/ AF?
AT Therapy
YES
P:R pattern information for each ventricular event
Rate information (ventricular cycle length; median atrial cycle length)
NO
Ventricular Arrhythmia Recording
AF Episode
Recording
Atrial
Rhythm
Classified
As:
AF
AT
Chapter 2
Tachyarrhythmia Detection and Monitoring
Post Mode Switch Overdrive Pacing – The Mode Switch
feature can be used to effect overdrive DDIR pacing immediately
after AT/AF termination. This is accomplished by programming a
higher Overdrive Rate and an appropriately long Overdrive
Period. For example, a patient can be paced at a Overdrive Rate
of 80 ppm for 2 minutes, in order to overdrive suppress a
recurrent, non-sustained atrial tachyarrhythmia.
Tachyarrhythmia Detection and Monitoring
The device receives two electrogram (EGM) signals through its
atrial and ventricular sensing leads, designated A and V. It
measures the time between sensed and paced atrial events to
determine the median atrial cycle length, and between sensed and
paced ventricular events to determine the ventricular cycle length.
The device also measures and analyzes the relationship between
P:R and R:P intervals to enhance the classification specificity for
atrial and ventricular tachyarrhythmias.
The device utilizes two independently functioning dual chamber
detection algorithms to classify tachyarrhythmias: an atrial
tachyarrhythmia (AT/AF) detection algorithm and a ventricular
high rate detection algorithm. Both algorithms are applied, as
programmed, to identify the cardiac rhythm following each sensed
ventricular event (Figure 2-2).
Figure 2-2. Detection and Therapy Flow Diagram
AT500 System Reference Guide
AT/AF Detection and Redetection
Dual chamber AT/AF detection combines P:R pattern information
with rate information to detect and classify non-1:1 atrial
tachyarrhythmias such as atrial flutter/tachycardia (AT) and atrial
fibrillation (AF).
On each ventricular event, the cardiac rhythm is evaluated by the
atrial tachyarrhythmia detection algorithm.
Preliminary AT/AF Detection – The device detects an AT/AF
episode when both:
■ the median atrial cycle length falls within one of the
programmed atrial tachyarrhythmia detection zones
(page 90),
■ the AT/AF Evidence Criterion (page 96) supports the
presence of an atrial tachyarrhythmia (i.e., greater than 1:1
A:V conduction, without far-field R-wave sensing).
Upon preliminary AT/AF detection, the device starts a Sustained
AT/AF Duration timer.
Overview
Tachyarrhythmia Detection and Monitoring
29
Sustained AT/AF Detection – If AT/AF episode duration
exceeds the programmed duration required to initiate therapy, the
device detects a sustained episode and stores the appropriate
episode data for later review via the programmer. If the atrial
rhythm is still classified as AT, the device can initiate the first
programmed AT therapy (page 110).
AT/AF Redetection – After the therapy delivery, the preliminary
AT/AF detection criteria are applied again. If the median atrial
cycle and AT/AF Evidence Criterion continue to support the
presence of an atrial tachyarrhythmia, the episode is redetected
as a sustained AT/AF episode and the next programmed AT
therapy can be initiated.
AT500 System Reference Guide
30
Chapter 2
Atrial Tachycardia (AT) Therapy
Ventricular Arrhythmia Monitoring
Dual chamber Ventricular Arrhythmia Monitoring uses PR Logic
Pattern and Rate Analysis to determine if a rhythm is a concurrent
double tachycardia (e.g., VF or VT in the presence of an SVT), a
rapidly conducted SVT, or VT or VF (see Figure 2-2).
If the ventricular cycle length is less than the programmed
ventricular monitoring interval, the device increments a VT event
counter in its memory. If the device counts 16 consecutive VT
events [Number of Intervals to Detect (NID)], the Medtronic AT500
applies PR Logic Pattern and Rate Analysis (page 103) to identify
a rapidly conducted SVT. If the rhythm is not identified by PR Logic
as a rapidly conducted SVT, the device stores the episode data as
a ventricular arrhythmia episode, for later review via the
programmer.
Atrial Tachycardia (AT) Therapy
Sustained episodes of AT/AF can be treated with up to three
separately programmed atrial antitachycardia pacing (ATP)
therapies. The device provides two types of ATP therapy for atrial
tachycardia:
■ A-Burst+ pacing (page 114)
■ A-Ramp pacing (page 116)
Following therapy delivery the next programmed therapy can be
initiated, if the AT/AF episode is redetected and the atrial rhythm
is still classified as AT. This progression continues for up to
48 hours per episode, until the device confirms termination of the
episode (page 100) or delivers all the programmed AT therapies.
AT/AF Sustained Duration Criterion – Automatic AT therapy is
withheld until the AT/AF episode duration exceeds the
programmed sustained duration value. The timer continues during
AT therapy delivery and redetection, and resets to zero when
AT/AF episode termination is detected.
Rhythm Classification – AT therapy is initiated only if the atrial
rhythm classification is AT (see “Atrial Rhythm Classification” on
page 92). If a sustained AT/AF episode is classified as AF, the
device stores the AF episode data and continues to monitor for
AT/AF episode termination or reclassification as AT.
AT500 System Reference Guide
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