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Electrophysiologic Effects of Dextro‐ and Levo‐Verapamil on Sinus Node and AV Node Function in Humans

The electrophysiologic effects of dextro (d)-and levo (l)-verapamil on sinoatrial (SA) and atrioventricular (AV) node function were studied in ten patients undergoing electrophysiologic evaluation of their supra-ventricular tachyarrhythmias. Both isomers elicited a significant prolongation of sinus node recovery time (SNRT) and AH interval. No difference between d- and l-verapamil regarding the magnitude of the effects, were observed. However, 50 mg d-verapamil was required to elicit the same electrophysiologic effects as 5 mg l-verapamil. The d- and l-verapamil plasma concentrations associated with the maximum effect on AH interval and SNRT showed a more than 20-fold difference (d: 380 ng/ml; l: 19 ng/ml). These data demonstrate that both verapamil isomers possess qualitatively similar slow channel blocking effects on the SA and AV node in humans, but the l isomer is 20 times more potent than the d isomer.