PO-04-024 THE SMALL HOURS OF THE NIGHT; VENTRICULAR PACING INHIBITION IN A HIS BUNDLE PACEMAKER

Abstract

Physiologic pacing is a promising alternative to conventional pacing with increasing utilization. We present a novel cause of pacing inhibition discovered after AV node ablation in a permanent His bundle pacing lead. Highlight a rare case of repetitive ventricular pacing inhibition due to internal validation and storage of an intracardiac electrocardiogram on the ventricular channel that occurred in a His bundle pacemaker. N/A An 85-year-old female with paroxysmal AF on flecainide, chronic RBBB, interstitial lung disease, SSS s/p dual chamber pacemaker with a His lead 4 years prior in anticipation of AV node ablation was admitted with highly symptomatic AF with RVR. With failure of both rhythm and rate control, she ultimately underwent successful AV node ablation. Overnight, telemetry showed AS-VP except for hourly events of a single sinus P wave without a following pacing spike or ventricular complex (Figure 1). Atrial and His lead parameters remained normal, and the device was programmed DDDR, not AAIR<-> DDDR. There was no farfield sensing of atrial or His signals on the ventricular channel. The pacemaker manufacturer (Medtronic), noted non-programmable intracardiac electrogram internal validation and storage that can occur every hour plus 30 seconds, but no sooner. During this storage process, ventricular pacing inhibition of a single cycle may occur due to residual electrical disturbance on the ventricular channel from turning on and off EGM collection, unrelated to conventional oversensing of intracardiac signals. The EGM collection must follow an atrial sensed event, consistent with telemetry findings. Thus far it has only been observed with Advisa pacemaker models, which utilizes sensitivity decay based on a ventricular sensed event. Once identified, the RV sensitivity is recommended to be decreased, in this case adjusted from 0.9mV to 2.8mV. This change prevented this phenomenon from re-occurring and the patient was doing well at follow-up 6 months later. This may be more common in His bundle pacing due to smaller R waves, higher V pacing burden, and use of this later model pacemaker. There is a broad differential for failure to pace, especially in a His bundle pacing lead. This case highlights a unique cause of hourly ventricular pacing inhibition, specific to this pacemaker model which may be frequently used in physiologic pacing, unrelated to traditional His lead oversensing.