Efficacy of amiodarone in the Wolff-Parkinson-White syndrome with rapid ventricular response via accessory pathway during atrial fibrillation.

Sudden death in Wolff-Parkinson-White syndrome (WPW) is related to a very fast ventricular response to spontaneous atrial fibrillation (AF) conducted via accessory pathway (AP). The effect of oral amiodarone was studied in 12 patients with WPW syndrome and life-threatening rapid ventricular response via an AP during spontaneous AF. The effective refractory period of the AP in the anterograde direction was 280 ms or less during control study in all patients. After amiodarone therapy, the effective refractory period remained 280 ms or less in 7 of the 12 patients. During incremental atrial pacing, the longest atrial pacing cycle length that produced block over an AP ranged from 200 to 310 ms (mean 261 +/- 42) during the control period and 240 to 980 ms (mean 377 +/- 198) after amiodarone therapy. During AF the shortest ventricular response via the AP could be measured in 10 of 12 of the patients both before and after amiodarone treatment and ranged from 200 to 290 ms (234 +/- 30) and 250 to 500 (mean 302 +/- 75), respectively (p less than 0.01). The average RR interval during AF before and after the drug ranged from 200 to 390 ms (mean 280 +/- 55) and 280 to 650 ms (mean 396 +/- 116), respectively (p less than 0.01). Thus, the safety of amiodarone in the WPW syndrome should be established by electrophysiologic studies and induction of AF, because amiodarone is not protective in all patients with WPW.

Evaluation of flecainide acetate in rapid atrial fibrillation complicating Wolff-Parkinson-White syndrome.

Flecainide is reported to be effective in patients with paroxysmal tachycardias, but its effect on rapid ventricular response over accessory atrioventricular pathway during atrial fibrillation is not known. The influence of flecainide on various electrophysiological properties of the accessory pathway with special emphasis on ventricular rate during atrial fibrillation was investigated in 9 patients with severe symptomatic Wolff-Parkinson-White syndrome. The shortest ventricular response during atrial fibrillation increased from 218 (190-270) to 320 (240-block) ms. In 4 patients sustained rapid atrial fibrillation converted to sinus rhythm. The rate of circus movement tachycardia decreased from 166/min to 130/min after flecainide, due to a lengthening of retrograde ventriculoatrial conduction time over the accessory pathway. Flecainide caused a significant prolongation of the effective refractory period of the accessory pathway in our subgroup with extremely fast AV conduction during atrial fibrillation and induced a depressant effect on retrograde accessory pathway conduction. This makes the drug very promising for the emergency treatment of dangerous rapid tachyarrhythias complicating this syndrome.