Thirty-three patients with supraventricular tachycardia associated with the Wolff-Parkinson-White syndrome were treated with encainide for 26 months (mean). Encainide at a mean dosage of 187 mg/day abolished or markedly decreased episodes of palpitations in 24 of 33 (73%), and no patient had syncope or required cardioversion while receiving the drug. Encainide was well tolerated and was discontinued in only 2 patients because of side effects (6%). Only 1 patient (3%) had a proarrhythmic effect while taking encainide (ventricular tachycardia). Fourteen of 16 patients (88%) with atrial fibrillation continue receiving encainide. Episodes of palpitations have been abolished or markedly decreased and no patient has had syncope or required cardioversion. All 14 of these patients had either anterograde block in the accessory pathway during atrial fibrillation or ≥75 ms increase in the shortest R to R interval formed by 2 preexcited QRS complexes. Encainide prolonged refractory periods of the atrial (p = 0.064) and ventricular (p = 0.061) muscle. It prolonged the cycle length at which 1:1 conduction of the accessory pathway in both the anterograde and retrograde directions occurred (both, p < 0.001). Induction of atrioventricular-reciprocating tachycardia (AVRT) was prevented in 36% of patients at repeat electrophysiologic study. The AVRT cycle length increased 112 ms (mean, p < 0.001) in those patients in whom AVRT was still inducible. The loss of delta waves recorded with the 12-lead scalar electrocardiogram during encainide therapy was a significant predictor of anterograde accessory pathway block (p < 0.001). No patient with a delta wave present developed anterograde or retrograde block in the accessory pathway. The shortest R to R interval formed by 2 preexcited QRS complexes during atrial fibrillation at control study was longer in those patients who developed anterograde (p = 0.06) and retrograde (p = 0.082) block in the accessory pathway. The atrial refractoriness was significantly shorter (p = 0.007) in those patients who developed retrograde block in the accessory pathway. Noninducibility of AVRT or ≥100 ms increase in the AVRT cycle length at repeat electrophysiologic study while patients received oral encainide was associated with longterm absence or markedly decreased incidence of palpitations and no patient had syncope or required cardioversion. Atrioventricular reentrant tachycardia was noninducible in all patients who developed retrograde block in the accessory pathway while receiving encainide therapy. All of these patients had markedly decreased or no recurrent palpitations and none had syncope or required cardioversion during long-term follow-up. Oral encainide is a well-tolerated form of chronic therapy for patients with supraventricular tachycardia associated with the Wolff-Parkinson-White syndrome.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine