2:1 AV tracking during DDD pacing during high output ventricular stimulation

Abstract

w t t i r t r t t n e “Pacemaker failure” occurred shortly after implant for omplete heart block in an 87-year-old woman, in an outide hospital. Ventricular outputs were increased, and the atient transferred. On arrival, 2:1 atrioventricular (AV) racking was observed. Interrogation revealed that the genrator was a Medtronic Prodigy DR 7860 (Medtronic, Mineapolis, MN), set to DDD 50 beats/min, mode switch off, VARP 310 ms; ventricular refractory 360 ms paced and ensed AV delay of 180 ms (without rate adaptive). Both trial and ventricular leads were bipolar active fix edtronic 4068s, with atrial output set to 5 V at 0.4 ms and ensitivity 0.5 mV, and ventricular output set to 7.5 V at 1.5 s, and sensitivity 2.8 mV. Lead impedances were in the ormal range for these leads. Telemetry demonstrated that, espite accurate atrial sensing, only alternate sinus beats ere tracked (Figure 1). Non-tracked beats were consisently followed by ventricular sensed events, “seen” by the acemaker, but without accompanying electrocardiogram vents. Programming to VVI mode at 50 beats/min revealed nderlying complete heart block with a slow ventricular scape rhythm (Figure 2). Native QRS complexes were ccurately sensed (ventricular sensed). However, ventricuar sensed events were also observed to occur after each entricular paced complex. These ventricular sensed events ad an identical coupling interval (560 ms) to ventricular aced complexes noted in Figure 1. The initial impression of the cause of this malfunction as a diagnosis of T-wave over-sensing during paced com-