HEART-RATE-VARIABILITY IN PATIENTS WITH VENTRICULAR ARRHYTHMIAS - EFFECT OF ANTIARRHYTHMIC DRUGS

The purpose of this study was to investigate whether heart rate variability could be reliably assessed in patients with ventricular arrhythmias and to evaluate whether it is affected by antiarrhythmic drugs. The study was based on an analysis of 239 ambulatory electrocardiographic (ECG) recordings obtained from 67 patients with frequent and complex ventricular arrhythmias enrolled in the Antiarrhythmic Drug Evaluation Group (ADEG) study. In each recording, after exclusion of premature ventricular complexes, the number of times during a 24 h period in which two consecutive sinus RR intervals differed by more than 50 ms was calculated. The total 24 h count from each recording was then used as an index of heart rate variability. This method is a reliable marker of cardiac parasympathetic activity. Recordings were analyzed at baseline (n = 56), during long-term treatment with amiodarone (n = 17), flecainide (n = 22) or propafenone (n = 17) and after washout in selected patients (n = 5). Despite the presence of a different number of arrhythmias, total 24 h counts in the same patient appeared reproducible over time (r = 0.83 between two different recordings, n = 49, p < 0.0001). Baseline counts (median 1,698, range 26 to 13,648) were not correlated (r = 0.15) with the number of arrhythmias. The three antiarrhythmic drugs had a disparate effect on total 24 h counts: no change was observed in patients treated with amiodarone (median percent change [DELTA%]-8, p = NS), whereas a significant (p < 0.025) decrease occurred in patients treated with flecainide (median DELTA%-56%) or propafenone (median DELTA%-64%). This effect was reversible after treatment was discontinued and was not related to suppression of arrhythmias because total 24 h counts were similar during treatment in the presence and absence of frequent arrhythmias. These results indicate that heart rate variability can reliably be assessed by this total 24 h counts method in patients with frequent ventricular arrhythmias. The presence or suppression of arrhythmias itself did not modify heart rate variability. Class IC antiarrhythmic drugs may significantly affect heart rate variability, and this influence may contribute to the overall effect of these agents on mortality.