Heart Rate Variability and Sudden Cardiac Death

BACKGROUND:

Sudden cardiac death usually is caused by malignant ventricular arrhythmias. Malignant
ventricular arrhythmias in coronary heart disease are due to an interplay among substrate
such as scarred ventricles, triggering events such as spontaneous ventricular arrhythmias,
and the autonomic nervous system. Non-invasive methods were needed to evaluate these three
components of risk in order to develop comprehensive detection and prevention programs.
Non-invasive screening tests for the arrhythmogenic substrate include left ventricular
ejection fraction and signal-averaged electrocardiograms, and for triggering events, the
24-hour continuous ECG recordings. Measures of heart rate variability defined as the
variability of the instantaneous heart rates or heart period variability defined as
variability of the normal R-R intervals may provide the means for non-invasive assessment of
autonomic nervous system activity. In previous studies it has been shown that a broad band
measure of heart period variability, the standard deviation of all normal R-R intervals in a
continuous 24-hour ECG recording made eight to fourteen days after myocardial infarction,
predicted mortality in the subsequent two to four years independently of left ventricular
dysfunction and spontaneous ventricular arrhythmias.

The six multicenter studies from which the data were drawn included: the Multicenter Post
Infarction Program (MPIP), a longitudinal, observational study of 867 patients; the
Multicenter Diltiazem Post Infarction Trial (MDPIT), a double-blind, randomized,
placebo-controlled trial of 2,466 patients; the Cardiac Arrhythmia Pilot Study (CAPS), a
double-blind, randomized, placebo-controlled trial of 502 patients; the Cardiac Arrhythmia
Suppression Trial (CAST), a double-blind, randomized, placebo-controlled trial of 4,200
patients; Electrophysiologic Studies Versus Electrocardiographic Monitoring (ESVEM), a
comparison of two methods for evaluating antiarrhythmic drug efficacy in 350 patients; and
the Cardiac Rate/Rhythm in Normal Adults, a cross-sectional observational study of 250
subjects.

DESIGN NARRATIVE:

Measurements of short and long-term heart rate and heart period variability were compared.
The day-to-day reproducibility and time course of change were determined in measures of
heart rate variability and heart period variability in patients with myocardial infarction.
The predictive accuracy of heart rate variability measured late after myocardial infarction
for subsequent mortality and development of malignant ventricular arrhythmias was
determined. Heart rate and heart period variability findings after myocardial infarction
were compared with those in age and sex-matched normal subjects and with those made in
patients with malignant ventricular arrhythmias.

Inclusion criteria

--Patients that have had myocardial infarction within 2 weeks - still in hospital and
sedentary except for short walks in hospital corridors

Exclusion criteria

--Inadequate 24-hour ECG recordings