RELATIONSHIPS BETWEEN HEART-RATE-VARIABILITY AND ANTIARRHYTHMIC EFFECTS OF HYDROQUINIDINE

Class I antiarrhythmic drugs may increase the incidence of cardiac dea th, and controlled treatment is required in patients with severe ventr icular arrhythmias. Electrophysiologically guided antiarrhythmic thera py remains an important method to manage patients with sustained ventr icular tachycardia (VT). The purpose of the study was to evaluate the correlations between baseline heart rate variability in ambulatory ele ctrocardiographic recordings of patients with sustained ventricular ta chycardia and the response to hydroquinidine on VT inducibility, and t o look for the changes in heart rate variability during hydroquinidine treatment. Thirty-five patients with spontaneous and inducible sustai ned VT were studied. Programmed ventricular stimulation and time and f requency domain analysis of heart rate variability were studied in the control state and 9-12 days after treatment with 300-600 mg of hydroq uinidine. In 11 patients (group I), hydroquinidine prevented VT induct ion. In 24 patients (group II), sustained VT remained inducible during treatment with hydroquinidine. In the control state, heart rate varia bility was similar in both groups. During treatment with hydroquinidin e, heart rate variability tended to decrease in groups I and II, but t he changes were significant only in group II: the coefficient of varia nce (CV) decreased from 13 +/- 4% to 10% +/- 3% (p < 0.01) and low fre quency/high frequency amplitude ratio decreased from 4.6 +/- 3.3 to 2. 87 +/- 2.42 (p < 0.05). In conclusion, baseline heart rate variability does not differentiate the responders and nonresponders to hydroquini dine. Hydroquinidine decreases heart rate variability in all patients, but principally in those with still inducible VT.