Inefficacy and proarrhythmic effects of flecainide and encainide for sustained ventricular tachycardia and ventricular fibrillation

Objective: To assess the efficacy of encainide and flecainide in treating patients with sustained ventricular arrhythmias. Design: Patients were treated with encainide or flecainide. Efficacy was assessed by comparing the results of programmed ventricular stimulation while patients received therapy with the results while they were drug free. Setting: The electrophysiology laboratory of the University of California at San Francisco. Patients: Forty-nine patients with spontaneous or inducible sustained ventricular tachycardia or ventricular fibrillation for whom treatment with at least one class IA antiarrhythmic agent had failed. Interventions: Patients were treated with encainide, 35 to 50 mg three or four times daily, or flecainide, 100 to 200 mg twice daily. Results: Arrhythmia worsened early in 5 of 16 patients receiving encainide and 3 of 33 patients receiving flecainide. Patients with poor left ventricular function were more likely to exhibit proarrhythmia (P = 0.02). Nine of eleven patients receiving encainide and 23 of 28 patients receiving flecainide who had repeat programmed ventricular stimulation while receiving drug therapy still had inducible, poorly tolerated ventricular tachycardia. Encainide and flecainide have a low efficacy rate and a high incidence of worsening of arrhythmia in patients with sustained ventricular arrhythmias, particularly when this condition is associated with poor left ventricular function.