Atrioventricular block in the atypical form of junctional reciprocating tachycardia: evidence supporting the atrioventricular node as the site of reentry.

Serial electrophysiologic studies were performed in 19 patients with the atypical form of supraventricular tachycardia having a long RP and short PR interval. In all 19 patients, supraventricular tachycardia was found to have a 1:1 P-QRS relation during initial control electrophysiologic studies, and in all 19 patients, electrophysiologic studies suggested that junctional reentry was the mechanism of supraventricular tachycardia. Seven of the 19 patients developed atrioventricular (AV) block during initiation of supraventricular tachycardia or after induction of supraventricular tachycardia following various drug administrations in subsequent studies. In three patients, second degree block within the His bundle or block distal to the His bundle recording site occurred after administration of quinidine. In one patient it occurred after procainamide, and in another patient it occurred after atropine. In one patient, 2:1 block proximal to the His deflection occurred after verapamil. In the remaining patient, a transient Wenckebach block proximal to the His deflection was noted after adenosine triphosphate. In this latter patient, 2:1 AV block was also noted after propranolol and digoxin. The site of reentry in these seven patients with AV block during supraventricular tachycardia was confined to the AV node area. Their supraventricular tachycardia did not involve a slowly conducting paraseptal accessory pathway because the distal AV node, His bundle and ventricle were not found to be necessary links in the tachycardia circuit.