Loss of efficacy of flecainide in the Wolff-Parkinson-White syndrome after isoproterenol administration.

Although anterograde conduction through a Kent bundle with a short refractory period was suppressed by 300 mg of flecainide acetate, the infusion of small amounts of isoproterenol caused the reappearance of WPW and permitted the induction of an atrial tachycardia with 1/1 conduction through the accessory pathway at a rate of 260 beats min-1. This case shows that the effect of isoproterenol may be maintained after apparently successful flecainide therapy.