Electrophysiologic and clinical effects of intravenous and oral encainide in patients with Wolff-Parkinson-White syndrome and paroxysmal atrial fibrillation

• Published in: European heart journal 1987-03, Vol.8 (3), p.282-290
• Main Authors: CHIMIENTI, M., MOIZI, M., SALERNO, J. A., KLERSY, C., GUASTI, L., PREVITALI, M., MARANGONI, E., MONTEMARTINI, C., BOBBA, P.
• Format: Article
• Language: English
• Subjects: Administration, Oral; Anilides - administration & dosage; Anilides - therapeutic use; artial fibrillation; Atrial Fibrillation - drug therapy; Atrial Fibrillation - physiopathology; Cardiac Pacing, Artificial; eletrophysiology; Encainide; Heart Conduction System - drug effects; Heart Conduction System - physiopathology; Humans; Injections, Intravenous; Wolff-Parkinson-White Syndrome - drug therapy; Wolff-Parkinson-White Syndrome - physiopathology; WPW syndrome
• ISSN: 0195-668X; 1522-9645
• DOI: 10.1093/oxfordjournals.eurheartj.a062271

The electrophysiologic effects of encainide were studied in 10 patients with Wolff–Parkinson– White syndrome after intravenous (1 mg kg−1 in 60 minutes) and oral administration of two dose regimens (75 and 150 mg daily). Under control conditions atrial fibrillation (AF) with a rapid ventricular response was induced in all patients andatrioventricular reciprocating tachycardia (A VRT) in 9 patients. After intravenous encainide AF was no longer induced in 3/9 patients; in 3 of the remaining the accessory pathway (AP) was totally blocked and in the others the shortest RR interval increased from 213 ±6 to 297 ±91 ms and the mean RR interval from 293 ± 39 to 362 ± 79 ms. The lower dose of oral encainide prolonged the shortest RR interval from 206 ± 24 to 273 ± 64 ms and the mean RR interval from 280 ± 48 to 368 ±52 ms in 6 patients; in 2 cases no preexcitedbeats were recorded and in 1 AF was not inducible. After the higher dose of oral encainide A F was still inducible in 7/8 cases; in 3 the A P was blocked and in the others the shortest and mean RR intervals increased from 202 ±30 to 280 ± 24 ms and from 276 ±59 to 436 ± 80 ms, respectively. After intravenous encainide antegrade conduction over the A P was blocked in 4/9 patients and the antegrade effective refractory period (ERP) was prolonged in another 4. Oral encainide blocked A P conduction in 4 cases and prolonged ERP considerably in the others. Induction of A V RT was prevented in 1/8 patients after intravenous and in 5/9 patients after oral encainide; in the 4 patients in whom AVRTremained inducible cycle length increasedfrom 306±31 to 3 54 ±49 ms after intravenous encainide and to 392 ±46 ms after oral administration. All patients were discharged on encainide (mean maintenance dose, 127 mg daily) and followed for 21 ±7 months; no recurrence of AF was observed; two patients complained of transient mild side effects. These data show that in patients with Wolff-Parkinson- White syndrome encainide prolongs refractoriness and slows conduction over the AP; it prevents induction of AVRT and markedly slows ventricular response during AF, thus protecting patients against life-threatening arrhythmias