Clinical electrophysiologic effects of encainide, a newly developed antiarrhythmic agent

Abstract

Encainide is a newly developed antiarrhythmic agent. With the use of intracardiac electrophyslologic techniques, its effects on the cardiac conduction system were examined in 10 patients with coronary artery disease. Five patients received 0.6 and five received 0.9 mg/kg body weight of encainide intravenously over 15 minutes. Plasma concentration, heart rate, blood pressure and conduction intervals (A-H, H-V, QRS and Q-T) were measured before, during and after encainide infusion. In addition, sinus nodal recovery time, Wenckebach cycle length, and atrial, atrioventricular (A-V) nodal and right ventricular refractory periods were measured before and after encainide infusion. The average peak plasma concentration was 0.49 ± 0.35 μg/ml (mean ± standard error of the mean). Encainide significantly prolonged H-V and QRS intervals in all patients by an average of 31 ± 7 and 18 ± 9 percent (standard deviation) ( P < 0.001), respectively. A minimal increase in the Q-T interval was also observed after encainide Infusion (2 ± 9 percent, P < 0.01), but no significant changes were noted in heart rate, blood pressure, A-H interval, corrected sinus nodal recovery time, Wenckebach cycle length or refractory periods of the atrium, A-V node or right ventricle. It is concluded that encainide significantly prolongs conduction in the His-Purkinje system without affecting conduction or refractoriness of other parts of the cardiac conduction system in man.