DUAL ATRIOVENTRICULAR NODAL PATHWAYS ASSOCIATED WITH A NODOVENTRICULAR TRACT INSERTING INTO THE LEFT VENTRICLE: A CASE REPORT

A patient with recurrent paroxysmal tachycardia of right bundle branch block morphology (RBBBM) and atrioventricular (AV) dissociation is demonstrated by electrophysiologic study to have dual AV nodal pathways and a unique left sided nodoventricular (NV) tract. Dual AV nodal pathway was manifest in three ways: sudden increment in AV nodal conduction in response to premature stimulation, double ventricular responses to single atrial extrastimuli and alternating fast and slow pathway conduction during right atrial (RA) programmed stimulation or RA overdrive pacing. The A-H interval of the fast pathway was 180 msec and that of the slow pathway was 290-330 msec. During RA stimulation, conduction over the slow pathway was associated with marked prolongation of AV conduction, decrease of the H-V interval (0-30 msec) and induction of a QRS morphology similar or identical to that recorded during spontaneous tachycardia. Tachycardia could be initiated by RA stimulation when impulses were conducted over the slow pathway or by right ventricular stimulation. The variation of QRS duration from 90-125 msec in RBBBM tachycardia indicated that the reentry circuit was confined to the AV node using the slow pathway as the antegrade limb and the fast pathway as the retrograde limb and that the anomalous tract was a NV fiber rather than a fascicaloventricular fiber.