Paroxysmal supraventricular tachycardia with Wenckebach block: evidence for reentry within the upper portion of the atrioventricular node.

Paroxysmal supraventricular tachycardia with Wenckebach block is an uncommon electrocardiographic finding. Electrophysiologic studies performed in a patient who exhibited this phenomenon indicated that the tachycardia was not caused by either sinus node or intraatrial reentry or abnormal automaticity. The tachycardia cycle length decreased after atropine administration and increased in response to propranolol. Administration of either adenosine (75 to 112.5 micrograms/kg) or verapamil (10 mg) terminated individual episodes of tachycardia. After verapamil and when atrial extrastimuli were introduced, dissociation of atrial activity from His-ventricular activity could be observed even though atrioventricular (AV) nodal block with a clear Wenckebach periodicity could also occur. These findings suggest that paroxysmal supraventricular tachycardia may be produced by reentry located solely within the upper portion of the AV node.