Verapamil-induced retrograde conduction block in a concealed atrioventricular bypass tract

Abstract

Reentrant supraventricular tachycardia (SVT) using a concealed bypass tract is a relatively common cause of narrow QRS complex tachycardia, accounting for 15 to 30% of cases in patients without evidence of preexcitation on the surface electrocardiogram. 1 The slow channel-blocking agent, verapamil, has been effective in the termination of such tachyarrhythmias, primarily through its actions on the atrioventricular node, with little effect on accessory atrioventricular (AV) pathways. 2–4 This report describes a patient with refractory SVT and a left-sided concealed bypass tract, in whom intravenous verapamil caused retrograde conduction block in the bypass tract.