A-V Nodal Reentrance

Electrophysiologic studies were performed in a patient with type B preexcitation and recurrent paroxysmal supraventricular tachycardia (PSVT). Atrial pacing at rates of 80/min and faster produced QRS normalization suggesting failure of the anomalous pathway. At a paced rate of 120/min, Wenckebach periods proximal to the His bundle as well as episodes of PSVT were noted. These episodes all occurred when a critical P-H interval of 300 msec was achieved. PSVT was also induced by coupled atrial pacing. At coupling intervals of 800-530 msec, anomalous pathway conduction was intact. At coupling intervals of 520 msec or shorter, QRS normalization occurred. At intervals of 480-280 msec, PSVT was induced. The P-H interval of the coupled beat inducing PSVT was always between 300 and 350 msec. Intraatrial recording revealed atrial echoes following each QRS of the PSVT. In summary, critical A-V nodal delay appeared necessary for induction of PSVT. This delay was achieved either by coupled pacing or during pacing-induced Wenckebach periods. The PSVT occurred at rates at which the anomalous pathway would seem to be inoperative. These findings strongly support A-V nodal reentry as the mechanism of PSVT in this patient without participation of the anomalous pathway. In this patient and other patients with similar flindngs, surgical ablation of the anomalous pathway would probably not be useful in prevention of recurrent PSVT.