Treatment of frequent ventricular arrhythmia with encainide: assessment using serial ambulatory electrocardiograms, intracardiac electrophysiologic studies, treadmill exercise tests, and radionuclide cineangiographic studies.

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Abstract
The effects of encainide on ventricular arrhythmia and left ventricular function were studied in 21 patients with chronic, high-grade ventricular arrhythmia using a prospective, 3-mo., placebo-controlled, single-blind trial design. Encainide caused a 96% decrease in the average hourly frequency of ventricular premature complexes (VPC) and comparable reductions in salvos of nonsustained ventricular tachycardia (VT) and episodes of sustained VT. Intracardiac electrophysiologic testing showed prolonged intraatrial and intraventricular conduction times and increased atrial, atrioventricular nodal, and ventricular refractory periods with both i.v. and oral encainide without His-Purkinje block, despite marked prolongation of HV and QRS intervals. Induced repetitive ventricular beating after ventricular extrastimuli in 15 patients showed persistent repetitive ventricular bearing with chronic oral encainide in 7 patients, 4 of whom had sustained VT within 2 mo. of treatment on encainide. Encainide did not reduce exercise capacity or left ventricular ejection fraction at rest or during supine exercise. Minor adverse effects of encainide in 11 of 21 patients included dose-related visual distubances, dizziness and sinus pauses (< 3 s). Major adverse effects included the new appearance of sustained VT in 3 of 20 patients (15%). Oral encainide effectively reduces the frequency and grade of VPC, prolongs intracardiac conduction times, and does not impair left ventricular performance. It is associated with frequent minor side effects and uncommon but potentially severe major side effects (sustained VT), both of which apparently have a direct relationship to the size of the dose.