Effects of flecainide on atrial electrophysiology in the Wolff-Parkinson-White syndrome.

The effects of intravenous flecainide and propafenone (2 mg/kg) administered in random order were compared in 16 patients with Wolff-Parkinson-White syndrome. Both agents prolonged significantly the anterograde refractory period of the pathway and caused complete anterograde block in the pathway in 5 patients. Atrial fibrillation was not inducible in 7 patients following both agents. Both drugs prolonged the minimum pre-excited RR interval, but this effect was significantly greater after flecainide than after propafenone. At a pacing cycle length of 500 msec, the atrial effective refractory period was unchanged after flecainide, but the atrial monophasic action potential duration, and the atrial monophasic action potential duration of the earliest inducible atrial beat were significantly increased. These results suggest that rate-dependent prolongation of atrial repolarization does not occur following clinical intravenous doses of flecainide. The prolongation of the repolarization of ectopic beats may prevent induction of atrial arrhythmias and may also have an important role in the termination of atrial fibrillation.