Verapamil effects in AV node reentry tachycardia with intermittent supra-Hisian AV block

The electrophysiologic details of two patients with atrioventricular (AV) node reentry tachycardia with intermittent 2:1 supra-Hisian block are presented. Both patients had clear evidence for atrial arrhythmias as well, emphasizing the need for a careful diagnostic analysis. Evidence supporting a diagnosis of AV node reentry tachycardia included: (1) short ventriculoatrial (VA) coupling intervals, (2) normal retrograde sequence of atrial activation, (3) dependence on critical AV node conduction times for initiation of tachycardia by atrial pacing, (4) ability to pace and capture the atria or ventricles without interrupting the tachycardia, and (5) fixed VA coupling intervals despite changes in tachycardia cycle length. Ten milligrams of verapamil was administered during sustained supraventricular tachycardia with 1:1 AV conduction, but despite prompt termination of tachycardia in both cases, 2:1 AV block was not induced. Atrial echoes could still be induced after verapamil, and diagnostic features (3) and (5) were particularly evident after the drug. Further analysis confirmed that verapamil did not have any observable effects on the likely site for supra-Hisian block--that is, the "final common pathway" of the AV node. This would support a contention that verapamil may have a selective effect on tissues within the confines of the AV node.