Heart Block in a Pacemaker: Does This Mean Trouble?

We present a finding in a 61-year-old woman whose St. Jude Medical dual-chamber permanent pacemaker had been implanted to treat symptomatic bradycardia. The pacemaker, programmed in DDD mode, had a lower rate limit of 60 beats/min and an upper limit of 120 beats/min, a paced atrioventricular (AV) delay period of 250 ms, and a sensed AV delay period of 225 ms.What happened during the first 3 complexes (Fig. 1)?A) Ventricular oversensing with inappropriate inhibition of ventricular pacing.B) Pacemaker-mediated AV delay attempting to allow intrinsic ventricular activity.C) Failure of ventricular capture with a ventricular escape rhythm.D) Pseudofusion of an attempted ventricular pacing event with a coincidental delayed ventricular complex.Fig. 1