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Transmission

Before being able to interpret the Ventricular run episode, we must understand the clinical context. This is a patient who has atrial fibrillation with rapid ventricular response, who has been implanted in preparation for His-bundle ablation, after which he will become completely dependent. More and more centers chose to implant a conduction system pacing lead as it allows a more physiological ventricular depolarization. As patients will become completely pacemaker dependent after His-ablation, implanters may opt to add a regular ventricular lead which serves as a back-up lead, in case the conduction pacing lead fails. It is recommended to connect the conduction system pacing to the atrial channel (in case of a dual chamber pacemaker) in order to not inhibit the back-up ventricular lead in case of lead noise. Also in this case, the conduction system pacing lead (3830) is connected to the atrial lead. This explains why on the Real time EGM and during the Ventricular run episode, the two EGM channels are very similar. This is not to be confused with atrial lead displacement, in which the atrial EGM will also look very much like the ventricular EGM as the atrial lead will have fall into the right ventricle. Using a dual chamber pacemaker in the context of conduction system pacing in combination with a ventricular back-up lead also needs a special pacing mode. Most often the DDI mode is used so that the events on the lead connected to the atrial channel does not trigger pacing of the lead connected to the ventricular channel. The trigger (As-Vp) is very useful when there is a lead within the atrium, but not when both leads are ventricular. In addition, in case of noise on the atrial channel, the ventricular (back-up) lead will continue to function as during VVI mode.

The ventricular run episode shows oversensing of fast and low-amplitude non-physiological artifacts. As the ventricular lead is pogrammed in unipolar sensing (which is to be avoided in general), it is probably the pectoral muscle which is responsable for the noise. The tracing shows that noise on the ventricular channel not only inhibits pacing on the ventricular channel, but also on the atrial channel. Therefore the tracing confirms the need of connecting the new technology (conduction system pacing) lead to the atrial channel, and not the ventricular channel, in sake of patient safety.

Next steps

The sensing polarity of the right ventricular lead should be switched from unipolar sensing to bipolar sensing. This will eliminate the risk of pectoral muscle oversensing and the associated risk of inappropriate inhibition of pacing by both pacing leads. In this case, this reprogramming was performed during hospitalization for His-ablation.