Heart Rate Variability and Dispersion of QT Interval in Patients With Vulnerability to Ventricular Tachycardi and Ventricular Fibrillation After Previous Myocardial Infarction

Objectives. This study was designed to compare QT dispersion measured from the standard 12-lead electrocardiogram and 24-h heart rate variability in patients with vulnerability to either ventricular tachycardi or ventricular fibrillation after previous myocardial infarction. Background. Increased QT interval dispersion and reduced heart rate variability have been shown to be associated with vulnerability to ventricular tachyarrhythmias, but the dat have mainly been pooled from patients with presentation of stable ventricular tachycardi and ventricular fibrillation. Methods. QT dispersion and time domain and two-dimensional vector analysis of heart rate variability were studied in 30 survivors of ventricular fibrillation with previous myocardial infarction and with inducible unstable ventricular tachyarrhythmi by programmed electrical stimulation and in 30 postinfarction patients with clinical and inducible stable monomorphic sustained ventricular tachycardia. Both of these patient groups were matched, with respect to age, gender and left ventricular ejection fraction, with an equal number of postinfarction control patients without history of arrhythmic events or inducible ventricular tachyarrhythmi and arrhythmia-free survival during follow-up period of 2 years. Forty-five age-matched healthy subjects served as normal control subjects. Results. Standard deviation of all sinus intervals and long-term continuous RR interval variability analyzed from Poincaré plots were reduced in patients with vulnerability to ventricular fibrillation (p < 0.001 for both), but not in patients with ventricular tachycardi (p = NS for both), compared with postinfarction control subjects. Corrected QT (QTc) dispersion was significantly broader both in patients with ventricular fibrillation (p < 0.001) and in those with ventricular tachycardi (p < 0.05) than in matched postinfarction control subjects. Heart rate variability performed better than QTc dispersion in predicting vulnerability to ventricular fibrillation. Conclusions. Increased QT dispersion is associated with vulnerability to both ventricular tachycardi and ventricular fibrillation. Low heart rate variability is specifically related to susceptibility to ventricular fibrillation but not to stable monomorphic ventricular tachycardia, suggesting that the autonomic nervous system modifies the presentation of life-threatening ventricular arrhythmias.