Effects of verapamil on supraventricular tachycardia in patients with overt and concealed Wolff-Parkinson-White syndrome.

Verapamil (0.15 mg/kg) intravenously, was administered to 19 patients with recurrent supraventricular tachycardia (SVT) undergoing electrophysiological evaluation. Twelve patients had overt Wolff-Parkinson-White (WPW) syndrome and seven patients had concealed accessory pathways conducting in the retrograde direction only. Verapamil had a significant effect in delaying conduction and prolonging refractoriness in the atrioventricular (AV) node, but no significant actions on any of the other cardiac tissues that formed the tachycardia circuit in these patients. In particular, it had no significant effects on anterograde or retrograde bypass conduction or refractoriness. Sustained SVT was initiated in 15 patients, and was terminated within 60 to 105 seconds of a 30-second injection of verapamil in 13 patients. Cycle length alternation during SVT was seen in six patients prior to reversion, and spontaneous ventricular complexes (VPCs) were observed following verapamil administration in five patients. Two patients with apparently normal sinus node function showed prolongation of their sinus node recovery times immediately following reversion of SVT by verapamil. Echo zones were assessed before and after verapamil, and sustained or self-terminating SVT could still be induced after the drug in 13 of the 15 patients who had sustained SVT beforehand. It was concluded that intravenous verapamil was effective in terminating sustained SVT in the majority of patients with overt or concealed WPW and that, despite a potential for sinus node depression and the initiation of VPCs, it had no clinically significant side effects. The ability to reinitiate SVT following its administration suggests the need for immediate follow-up with maintenance drug therapy.