We performed electrophysiologic studies in 19 patients with accessory pathways before and during encainide therapy with a mean daily dose of 197 mg. Fourteen patients had manifest accessory atrioventricular connections, and 5 patients had concealed accessory atrioventricular connections. The patients had recurrent atrioventricular reentrant tachycardia for a mean of 15.8 years and had received a mean of 3.6 drug trials without successful suppression of recurrent arrhythmias. Encainide caused complete antegrade conduction block in the accessory pathway in 8 of 14 patients with manifest accessory atrioventricular connections. The shortest atrial pacing cycle length maintaining 1:1 conduction over the accessory pathway at control study was 328 ± 66 msec in patients in whom antegrade conduction block occurred, and it was 247 ± 21 msec (p < .01) in patients in whom conduction remained during encainide therapy. Retrograde conduction over accessory atrioventricular connections could be evaluated in 14 patients, and complete block occurred in 7 patients during encainide therapy. There was no correlation between control retrograde effective refractory period or conduction of the accessory pathway and subsequent development of conduction block with encainide therapy. It should be noted that 5 patients who developed drug-related retrograde block over the accessory pathways had initial retrograde effective refractory periods for the accessory pathway less than 270 msec. Nineteen patients had atrioventricular reentrant tachycardia initiated at control electrophysiologic study. Encainide prevented induction of tachycardia in 10 patients, and in the other 9 patients, cycle length of tachycardia increased during drug treatment from 313.9 ± 53.1 to 418.3 ± 80.9 msec (p < .001), primarily due to an increase in ventriculoatrial conduction time from 162.2 ± 43.8 to 238.3 ± 87.9 msec (p < .01). Fifteen patients continued encainide treatment for a mean of 18 months (range 7 to 38), and all but one patient remain asymptomatic. Encainide is well tolerated and prevents recurrence of reentrant tachycardia in patients with Wolff-Parkinson-White syndrome very effectively.
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine
- Physiology (medical)