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Managed Ventricular Pacing Facilitating Atrioventricular Nodal Reentrant Tachycardia

An 81-year-old woman with a history of coronary artery disease (left ventricular ejection fraction of 50%) and severe pulmonary hypertension underwent placement of a dual-chamber pacemaker (EnRhythm, P1501DR, Medtronic, Inc., Minneapolis, MN, USA) to treat episodes of syncope caused by a junctional rhythm at a rate of 30 beats/min following episodes of narrow complex tachycardia. To preserve native ventricular activation, the device was programmed to a rate responsive mode, AAIR/DDDR (managed ventricular pacing, MVP) with a lower rate limit of 60 pulses/min (ppm) and an upper rate limit of 120 ppm. The patient subsequently had recurrent episodes of paroxysmal, short-RP tachycardia on ECG (Fig. 1). Intracardiac recordings from the device showing initiation and ventricular pacing during supraventricular tachycardia (SVT) are shown in Figures 2(A) and (B). Reprogramming the device to the DDDR mode with a paced atrioventricular (AV) interval of 180 ms and a sensed AV interval of 150 ms prevented further episodes of tachycardia. What is the explanation?