GE HEART RATE TURBULENCE PHYSICIAN'S GUIDE_SM_2020044-105_A BMET Trigonometry

Heart Rate Turbulence

Physician’s Guide

2020044-105 Revision A

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T2 Heart Rate Turbulence 2020044-105A

1 November 2005

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Manual Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

The HRT-Algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Quantification of HRT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Analysis Option Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Assessment of the Heart Rate Turbulence Analysis Results . . . . . . . . . . . . . . . . . . 9

Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Limits of Heart Rate Turbulence Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Related Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2020044-105A Heart Rate Turbulence 1

2 Heart Rate Turbulence 2020044-105A

Introduction

Manual Overview

Revision History

Purpose

Each page of the document has the document part number and revision
letter at the bottom of the page. The revision letter identifies the
document’s update level.

Revision History, PN 2020044-105

Revision Date Comment

A 1 November 2005 Initial release of this manual,

corresponds with version 1.0 of the Heart
Rate Turbulence Software.

This manual contains descriptions of Heart Rate Turbulence (HRT) and
the measurement of HRT to help the clinician understand how the HRT
measurement software works and how to most effectively use HRT
applications. This manual contains an overview of HRT, examples of
measurements made by GE systems, and the theory behind measuring
HRT.

Intended Audience

Intended Use

This manual is intended for qualified health care professionals using the
heart rate turbulence option in hospitals, doctor’s offices, or other clinical
environments.

The Heart Rate Turbulence (HRT) analysis program is intended for use
in a hospital, doctor’s office, or clinic environment under the direct
supervision of a licensed health care practitioner. The intended use of the
HRT analysis program is to analyze ECG signals, provide measurements
of HRT in patients undergoing cardiovascular disease testing for
interpretation by qualified by health care practitioners for the purposes
of risk stratification and prediction of sudden cardiac death. The HRT
analysis program only provides measurements, not interpretations. The
HRT program is to be used in conjunction with the patient’s clinical
history, symptoms, and other diagnostic tests for final clinical judgment.

2020044-105A Heart Rate Turbulence 1

Overview

CAUTION

INTERPRETATION — Interpretation of the HRT
analysis must be confirmed by a qualified physician or
cardiologist, and should be used only as an adjunct to
clinical history, symptoms, and the results of other non­invasive and or invasive tests.

Heart Rate Turbulence (HRT) is the physiological, bi-phasic response of
the sinus node to premature ventricular contractions. It consists of a
short initial acceleration followed by a deceleration of the heart rate.
HRT can be quantified by two numerical parameters, namely the
Turbulence Onset (TO) and the Turbulence Slope (TS). The underlying
mechanisms of HRT have not been fully identified.

HRT is most probably an autonomous baroreflex. The premature
ventricular contraction causes a brief disturbance of the arterial blood
pressure (low amplitude of the premature beat, high amplitude of the
ensuing normal beat). When the autonomic control system is intact, this
fleeting change is registered immediately with an instantaneous
response in the form of HRT. If the autonomic control system is
impaired, this reaction is either weakened or entirely missing.

PVC

001A

Figure 1

Figure 1 shows premature ventricular contraction (PVC) and its impact
on the arterial blood pressure. The blood pressure has impact to the
baroreceptors. HRT is most probably an autonomous baroreflex.

HRT analysis is suitable for assessing the risk following myocardial
infarction. After analyzing the data of more than 5,000 post-infarction
patients, it was established that HRT is — independent of other risk
predictors — the most powerful ECG-related risk predictor.

2 Heart Rate Turbulence 2020044-105A

The HRT-Algorithm

Quantification of HRT

9A

The predictive value of HRT is comparable with that of the ejection
fraction of the left ventricle.

Turbulence Onset (TO) is the percentage difference between the heart
rate immediately following PVC and the heart rate immediately
preceding PVC. It is calculated using the equation

TO = 100 * ((RR

with RR
PVC and RR1 and RR2 the first two normal intervals following the PVC.
Initially, TO is determined for each individual PVC, followed by the
determination of the average value of all individual measurements.
Positive values for TO indicate deceleration of the sinus rhythm, and
negative values indicate acceleration of the sinus rhythm.

2020044-105A Heart Rate Turbulence 3

and RR-1 being the first two normal intervals preceding the

-2

+ RR2) - (RR-2 + RR-1)) / (RR-2 + RR-1)

1

002A

Figure 2

Figure 2 shows Turbulence Onset (TO) the percentage difference
between the average value of the first two normal intervals following the
PVC and the last two normal intervals preceding the PVC. Initially, TO
is determined for each individual PVC, followed by the determination of
the average value of all individual measurements.

003A

Figure 3

Figure 3 shows the TS, the steepest slope of a linear regression line
through five consecutive measurement points in the averaged
tachogram. The TS calculations are based on the averaged tachogram
and expressed in milliseconds per RR interval.

Filters

The algorithm for HRT quantification can only deliver usable results if
the triggering event was a true PVC (and not an artifact, T-wave or

4 Heart Rate Turbulence 2020044-105A

something similar). Also, the sinus rhythm immediately preceding and
following the PVC is free from arrhythmia, artifacts and false
classifications. In order to fulfill these requirements, filters are used to
reject HRT calculation. Rejection is provoked by RR intervals with the
following characteristics:

 < 200 milliseconds

 > 2500 milliseconds

 > 200 milliseconds difference to the preceding sinus interval

 > 20% difference to the reference interval (mean of the 5 last sinus

intervals)

In addition, the HRT calculations are limited to PVCs:

 with a minimum prematurity of 20%

 with a post-extrasystole interval which is at least 20% longer than

the normal interval

 having 2 normal RR intervals before

 having 15 normal RR intervals after

Analysis Option Definitions

The analysis options for HRT can be configured on the MARS system in
System >> System Setup >> Analysis Options >> HRT.

2020044-105A Heart Rate Turbulence 5

Turbulence Onset

This is the percentage difference between the averaged value of first two
normal intervals following the PVC and the last two normal intervals
preceding the PVC.

Turbulence Slope

This is the steepest slope of the linear regression through five
consecutive measurements in the averaged tachogram.

Turbulence Correlation

This is the steepest correlation coefficient of the linear regression
through five consecutive measurements in the averaged tachogram.

10A

6 Heart Rate Turbulence 2020044-105A

Reference Interval

The reference interval is the mean of the 5 normal to normal RR
intervals prior to the trigger. The reference interval serves as a measure
of the actual heart rate. Some RR interval filters used in the HRT
algorithm refer to the reference interval, e.g. the 80% PVC coupling
interval filter.

Single Premature PVC with Compensatory Pause

A PVC that is enclosed by normal beats AND with a coupling interval
(the RR interval between the last normal and the PVC) that is less than
80% of the reference interval AND with a post-extrasystolic pause (the
RR interval following the PVC) that is greater than 120% of the reference
interval

This is the criteria for PVCs that are selected in the HRT algorithm.

Percent RR to Call a Normal RR Premature

For the calculation of the HRT tachogram, target sequences containing
highly varying normal-to-normal intervals are eliminated. This value
controls the amount of prematurity (expressed in percentage units) to
exclude a target sequence. For example (with this limit set to 20%) a
potential target sequence will be eliminated if it will include two
consecutive normal-to-normal intervals (RR1 and RR2) such that RR2 <

0.8*RR1.

Percent RR to Call a Normal RR Late

This parameter is the same as previous one but used to control how late a
normal RR interval will be. For example (with this limit set to 20%) a
potential target sequence will be eliminated if it will include two
consecutive normal-to-normal intervals (RR1 and RR2) such that RR2 >

1.2*RR1.

Max Difference to Call a Normal RR Premature or Late

The concept is the same of previous two variables, i.e. to control target
sequences containing highly varying normal-to-normal intervals. This
variable controls the absolute difference between two consecutive RR
intervals. For example (with this limit set to 200 msec) a potential target
sequence will be eliminated if it will include two consecutive normal-to-

2020044-105A Heart Rate Turbulence 7

normal intervals (RR1 and RR2) such that RR2 > RR1+200 or if RR2 <
RR

-200.

1

Percent Value to Call a PVC RR Premature and Percent Value to Call
a PVC RR Late

PVC related intervals are defined as the RR intervals directly adjacent to
a ventricular premature beat, i.e. the coupling interval and
compensatory pause. For the calculation of the HRT tachogram, target
sequences are eliminated when the coupling interval or post­extrasystolic pause are shorter than a percent value of the reference
interval. The two percent thresholds are controlled by the premature and
late variables. For example (with both variables set to 20%), a target
sequence will be eliminated if the coupling interval is > 80% of the
reference interval or if the post-extrasystolic pause is < 120% of the
reference interval.

Minimum Value for an RR to be Included

A target sequence will be eliminated if one of the RR intervals in the
tachogram will be shorter than this limit.

Pause

RR Before

RR After

A target sequence will be eliminated if one of the RR intervals in the
tachogram will be longer than this limit.

This variable determines how many RR intervals before the target
events are included in the analysis. The code that draws the HRT
tachogram considers this variable when determining the number of RR
intervals to draw.

This variable determines how many RR intervals after the target events
are included in the analysis. The code that draws the HRT tachogram
considers this variable when determining the number of RR intervals to
draw.

8 Heart Rate Turbulence 2020044-105A

Assessment of the Heart Rate Turbulence Analysis Results

Identification of high-risk patients after acute myocardial infarction is
essential for successful prophylactic therapy. The absence of the Heart
Rate Turbulence after ventricular premature beats is a very potent
postinfarction risk stratifier that is independent of other known risk
factors and which is stronger than other presently available ECG-based
risk predictors [1].

Absence of HRT is defined by the TO, the TS, and the combination of
both TO and TS, namely:

Scenario 1 — TO > 0%, or

Scenario 2 — TS < 2.5 milliseconds/RR interval, or

Scenario 3 — TO > 0% and TS < 2.5 milliseconds/RR interval

The highest predictive power is shown in scenario 3.

With the population of the Multicentre Post-Infarction Program, and the
population of the European Myocardial Amiodarone Trial, risk ratios of

3.2 were achieved [1]. In another population even a risk ratio of 5.9 was
achieved [2]. The risk, or hazard ratio is calculated from Kaplan-Meyer
survival curves, and is approximately the ratio of the percentages of
those people who died with fulfilling the criteria for scenario 3 above and
the percentage of those people who died without fulfilling the criteria for
scenario 3 above.

004A

Figure 4

2020044-105A Heart Rate Turbulence 9

Figure 4 shows the HRT analysis results of a low risk patient (TO < 0%,
TS > 2.5 milliseconds/RR interval). The number of episodes with detected
isolated PVCs (triggers) was 60. The averaged tachogram represents all
detected episodes with a PVC that met the filter/inclusion criteria.

005A

Figure 5

Figure 5 shows the HRT analysis results of a high risk patient (TO > 0%,
TS 2.5 milliseconds/RR interval). The number of episodes with detected
isolated PVCs (triggers) was 139. The averaged tachogram represents all
detected episodes with a PVC that met the filter/inclusion criteria.

Prerequisite for good HRT analysis results are true PVCs. Artifacts for
example, when they are misinterpreted as PVCs, can change the
representative average tachogram, causing the resulting TO and TS to
become erroneous. Because of this, the HRT option has filters (see

“Filters” on page 4) implemented to exclude tachograms with false

positive PVCs. The filter settings are configurable by the user. Normally
these filter settings are sufficient but it can be useful to change them in
order to get better results for a single patient.

The HRT option provides graphical displays to give the user the
possibility to assess the correctness of the averaged tachograms (see
figures 4 and 5). Those possibilities are

 all used tachograms one upon the other (superimposed, see figure 6).

Outliers are visible in this diagram.

 possibility to display every single tachogram, with the ability to

delete it (see figure 7), removing it from the averaged tachogram.
This is shown with the corresponding ECG episode.

 possibility to display every excluded tachogram (see figure 8).

10 Heart Rate Turbulence 2020044-105A

Figure 6

Figure 6 shows all used tachograms one upon the other (superimposed).

006A

007A

Figure 7

Figure 7 shows a single tachogram (above) together with the
corresponding ECG episode (below). The user has the possibility to delete
the tachogram, if it is not correctly labeled as a true PVC. After the
deletion, it will not be part of the averaged tachogram, and it will not be
included in the TO and TS measurements.

2020044-105A Heart Rate Turbulence 11

Reports

008A

Figure 8

Figure 8 shows an excluded single PVC (above) together with the
corresponding ECG episode (below). The reason for its exclusion is the
2nd PVC, which is inside 15 RR intervals (see “Filters” on page 4).

Three different HRT report components are available for the HRT tool on
the MARS Holter Analysis Workstation. These are configured in the
System >> System Setup >> Report Configuration interface:

 HRT - Averaged Tachogram,

 HRT - Superimposed Tachogram, and

 HRT - Option Settings

These components may be included in any of the pre-defined report
setups and/or be included in a user-defined report setup.

If the environment variable HRT_RESEARCH_OUTPUT is set to any
value, a file containing the beat position and beat class for all triggers is
written to a file. The file name is the slot file name without the .nat
extension.

12 Heart Rate Turbulence 2020044-105A

Limits of Heart Rate Turbulence Analysis

HRT is not always measurable. HRT obviously cannot be measured in
patients who do not have PVCs. Also, it cannot be measured in patients
with pacemaker rhythm or episodes of atrial fibrillation for the duration
of the Holter recording.

Related Reading

Schmidt G. et al. Heart-rate turbulence after ventricular premature
beats as a predictor of mortality after acute myocardial infarction. Lancet
353:9162 1390–1396 (1999).

Barthel P. et al. Risk stratification after acute myocardial infarction by
heart rate turbulence. Circulation 108 1221–1226 (2003).

Ghuran, A. et al. Heart rate turbulence-based predictors of fatal and
nonfatal cardiac arrest (The autonomic tone and reflexes after
myocardial infarction substudy). American Journal of Cardiology; Vol.
89:2 184–190 (2002).

Watanabe M.A. et al. Effects of ventricular premature stimulus coupling
interval on blood pressure and heart rate turbulence. Circulation, 106
325-330 (2002).

2020044-105A Heart Rate Turbulence 13

14 Heart Rate Turbulence 2020044-105A

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