HEART-RATE-VARIABILITY AND DISPERSION OF QT INTERVAL IN PATIENTS WITHVULNERABILITY TO VENTRICULAR-TACHYCARDIA AND VENTRICULAR-FIBRILLATIONAFTER PREVIOUS MYOCARDIAL-INFARCTION

Objectives. This study was designed to compare QT dispersion measured from the standard 12-lead electrocardiogram and 24-h heart rate variab ility in patients with vulnerability to either ventricular tachycardia or ventricular fibrillation after a previous myocardial infarction, B ackground. Increased QT interval dispersion and reduced heart rate var iability have been shown to be associated with vulnerability to ventri cular tachyarrhythmias, but the data have mainly been pooled from pati ents,vith presentation of stable ventricular tachycardia and ventricul ar fibrillation, Methods, QT dispersion and time domain and two-dimens ional vector analysis of heart rate variability were studied in 30 sur vivors of ventricular fibrillation with a previous myocardial infarcti on and,vith inducible unstable ventricular tachyarrhythmia by programm ed electrical stimulation and in 30 postinfarction patients with clini cal and inducible stable monomorphic sustained ventricular tachycardia , Both of these patient groups were matched, with respect to age, gend er and left ventricular ejection fraction, with an equal number of pos tinfarction control patients without a history of arrhythmic events or inducible ventricular tachyarrhythmia and arrhythmia-free survival du ring a follow-up period of 2 years, Forty five age-matched healthy sub jects served as normal control subjects, Results, Standard deviation o f all sinus intervals and long-term continuous RR interval variability analyzed from Poincare plots were reduced in patients with vulnerabil ity to ventricular fibrillation (p < 0.001 for both), but not in patie nts,vith ventricular tachycardia (p = NS for both), compared with post infarction control subjects, Corrected QT (QTc) dispersion was signifi cantly broader both in patients with ventricular fibrillation (p < 0.0 01) and in those with ventricular tachycardia (p < 0.05) than in match ed postinfarction control subjects, Heart rate variability performed b etter than QTc dispersion in predicting vulnerability to ventricular f ibrillation, Conclusions, Increased QT dispersion is associated with v ulnerability to both ventricular tachycardia and ventricular fibrillat ion. Low heart rate variability is specifically related to susceptibil ity to ventricular fibrillation but not to stable monomorphic ventricu lar tachycardia, suggesting that the autonomic nervous system modifies the presentation of life-threatening ventricular arrhythmias. (C) 199 7 by the American College of Cardiology.