Encainide for refractory ventricular tachyarrhythmia

Encainide, a new antiarrhythmic agent, was studied in 80 patients with sustained ventricular tachycardia or ventricular fibrillation. Drug efficacy was evaluated by ambulatory monitoring and exercise testing in 63 patients who had frequent or repetitive ventricular premature beats and by means of electrophysiologic testing in 17 patients who did not have significant arrhythmia during a 48-hour control period. Encainide was effective in 36 of 63 patients (57%) as judged by ambulatory monitoring and in 35 of 51 patients (69%) who had exercise tests while taking the drug. Overall, 34 patients (54%) responded to encainide when evaluated by both monitoring and exercise testing. The drug was effective in 7 of 16 patients (44%) who underwent electrophysiologic studies. Daily doses and blood levels of encainide were Comparable in responders and nonresponders. Toxicity occurred in 24 patients (30%) and included nausea, vomiting, headaches, lethargy, tremors and conduction disturbances. In 18 patients (23%) arrhythmia was aggravated. An increase in arrhythmia correlated with larger daily doses of encainide and higher serum blood levels of encainide and its metabolite OD-methyl-encainide, but did not correlate with QRS- or QT-interval widening. Of the 27 patients who were discharged on encainide, 23 were maintained on the drug for an average of 21 months (range 12 to 44). Three patients died suddenly.Thus, encainide is a useful agent for suppression of malignant ventricular arrhythmias. However, it has a high potential for worsening arrhythmias and careful evaluation by both monitoring and exercise testing is necessary to judge its effect.