Long-term follow-up of incessant supraventricular tachycardia treated with oral encainide.

The long-term follow up (32 to 44 months, mean 37 months) of 9 patients with incessant supraventricular tachycardia treated with oral encainide is reported. During that follow up period, 1 patient developed an 'escape' phenomenon to encainide and incessant supraventricular tachycardia recurred in spite of increasing doses of encainide. Two patients required electrical fulguration of the bundle of His because of inability to control incessant supraventricular tachycardia. One patient discontinued treatment without suffering from recurrences of the arrhythmia. In 6 of the original 11 patients treated with oral encainide, antiarrhythmic efficacy persisted after a mean of 3 years. No additional long-term side effects developed. It is concluded that the antiarrhythmic efficacy of oral encainide in incessant supraventricular tachycardia persists long-term, although some patients may develop an 'escape' phenomenon to encainide while others develop spontaneous cure of tachycardia.