Intravenous verapamil for termination of re-entrant supraventricular tachycardias: intracardiac studies correlated with plasma verapamil concentrations.

We evaluated efficacy and mechanisms of the antiarrhythmic action of verapamil in 20 patients with sustained supraventricular tachycardia. Two patients had sinus nodal re-entrant tachycardia, nine atrioventricular (AV) nodal re-entrant tachycardia, and nine AV reciprocating tachycardia associated with the Wolff-Parkinson-White syndrome. The study design comprised a double-blind, randomized, cross-over phase using a 0.075 mg/kg dose of verapamil versus placebo and an open-label phase using a 0.15 mg/kg dose of verapamil. The overall results of both phases showed that 15 of 19 patients converted to sinus rhythm with verapamil while only one of 16 converted to sinus rhythm with placebo. The effective plasma verapamil concentration measured 123 +/- 40 ng/mL (mean +/- SD). Verapamil suppressed sinus nodal and AV nodal re-entry but exerted no selective depression between fast and slow AV nodal pathways. It had no significant effect on accessory AV bypass tract but was effective in terminating AV reciprocating tachycardia by its depressive action on the AV node.