Role of adrenergic stimulation by isoproterenol in reversal of effects of encainide in supraventricular tachycardia.

Reversal of the electrophysiologic effects of oral encainide with isoproterenol was evaluated in 16 patients with atrioventricular (AV) nodal reentry (group A) and in another 16 patients with Wolff-Parkinson-White syndrome (group B). Sustained AV nodal reentry was induced in all group A cases before administration of encainide, in 2 cases after oral encainide, and in 12 patients during infusion of isoproterenol. Among group B cases, 14 of 16 had sustained AV reentry during control, 6 of 16 after receiving encainide, and 8 of 16 with addition of isoproterenol. During a mean follow-up of 19 +/- 10 months in group A and 17 +/- 9 months in group B, clinical tachycardia recurred in 8 patients (4 from each group). These 8 patients were among the 20 patients who demonstrated (1) isoproterenol-induced reversibility of encainide-suppressed tachycardia, or (2) acceleration of tachycardia rate slowed by encainide. No recurrences were seen among any of the 12 cases in which isoproterenol failed to reverse the encainide-induced tachycardia suppression. Patients with clinical recurrences were controlled with a variety of means, which included beta blockers in 3 and nonpharmacologic methods in the remaining 5. In patients with AV junctional tachycardia treated with oral encainide, our findings suggest that lack of tachycardia inducibility with isoproterenol predicts freedom from clinical recurrences. Furthermore, addition of a beta blocker to oral encainide may prevent clinical recurrence in some who demonstrate adrenergic reversal of encainide effect.