Optimal his bundle pacing programming in patients with permanent atrial fibrillation
Authors: Piemontese G.P , Bartoli L , Statuto G , Angeletti A , Massaro G , Martignani C , Ziacchi M , Biffi M 
Published: October 2021

Abstract

Background
Interest in permanent His bundle pacing (HBP) as a means of both preventing pacing-induced cardiomyopathy and providing physiological resynchronization by normalization of His-Purkinje activation is constantly growing. Current devices are not specifically designed for HBP, which gives rise to programming challenges.

Purpose
To evaluate the critical troubleshooting HBP options in patients with permanent atrial fibrillation (AF) and variable degree of atrio-ventricular block (AVB) who receive HBP through a lead connected to the atrial port, and an additional ventricular “backup”.

Methods
Between December 2018 and March 2021, 136 consecutive patients with indication for pacing underwent HBP. Among these, 24 had permanent AF with documented symptomatic pauses. Seven of them received a dual-chamber device which was used to place a backup right ventricle (RV) lead; in this scenario, the His lead is implanted in the right atrial (RA) port, the RV lead in the RV port. Depending on the presence of an additional left ventricle (LV) lead, either a dual-chamber and a CRT device can be used.

Results
In this context, the events marked as atrial sensed (As) or paced (Ap) are indeed ventricular, so that sensing is more complex. A clinical scenario is atrial activity oversensed on the His channel (As) leading to RV dyssynchronous pacing in the ventricular safety pacing (VSP) window. A second one is intrinsic QRS undersensing causing inappropriate His pacing with possible delivery of the RV pulse depending on capture of the His pulse. The interplay of intrinsic ventricular activity (rate, signal amplitude and slew rate on both the His and the ventricular channel) and of the HV interval may be of key importance to troubleshoot As-Vp (atrial sensed – ventricular paced) [Fig. 1A] as well as Vs-Ab (ventricular sensed – atrial blanking period) sequences [Fig. 1B]. Changing sensitivity and sensing configuration may help or fail to fix these issues depending on the abovementioned aspects, making it mandatory to check that the paced AV delay is appropriately set as to avoid inappropriate RV pacing on the T wave of an undersensed intrinsic event at the His channel. DVI(R) mode programming may indeed prove safer than DDD(R) in the setting of preserved intrinsic activity or in the event of intermittent His capture loss.
Paced AV delay should be programmed slightly longer than H-V+QRS duration to avoid unnecessary RV pacing with pseudo-fusion (too short) and possibly R/T events (too long). Stability of H-V interval and of QRS duration must be verified at each device follow-up by decremental His pacing to ensure consistent sensitivity of the ventricular signal beyond stable His capture, that may be challenged by infra-hisian block.

Conclusions
Owing to the absence of HBP-specific devices, HBP shall be made safe and effective by careful troubleshooting, consisting of sensitivity setting, paced AV interval and mode programming.

Funding Acknowledgement
Type of funding sources: None. Different sensitivity settings for HBP