His bundle pacing: development of chronic thresholds - a single-center experience over 8 years in 529 patients

Conduction system pacing (CSP) is increasingly used to avoid the development of pacing-induced cardiomyopathy in patients who require a high amount of ventricular pacing. His bundle pacing (HBP) leads to a physiologic ventricular activation via His-Purkinje conduction system. It is considered as ideal to achieve the narrowest paced QRS and optimal synchronization in patients with intrinsic narrow QRS or right bundle branch block, there are however concerns about low implantation success rates and an acute and chronic threshold increase.

The aim of this study was to analyze our experience with HBP in terms of implantation success rate, chronic pacing thresholds, the incidence of dislodgements and consecutive clinical events.

In this single center registry, all consecutive patients in whom HBP was attempted during the period from June 2016 to October 2024 were enrolled prospectively. Data on patient characteristics, medical history, implantation success, sensing and pacing parameters over 36 months were collected. Furthermore, threshold increase ≥3.5V/1.0 ms, loss of capture, His bundle lead dislodgement and consecutive clinical events were analyzed.

HBP was attempted in 529 patients (78±18 years, 39% female, 92% AV block, left ventricular ejection fraction 53±10%, 93 single-, 352 dual-, 56 triple-chamber pacemakers, 4 dual- and 24 triple-chamber ICDs). HBP implantation was successful in 503 (95.1%) of these patients (222 non-selective HBP, 254 selective HBP, and 17 LBBAP). Sensing and pacing parameters at implantation and during follow-up are shown in the Figure. Over time, there were 19 (3.6%) pacing threshold increases ≥3.5V/1.0 ms, 1 (0.2%) loss of capture (patient with sinus node disease) and 4 (0.7%) lead dislodgements (2 patients with Twiddler syndrome), in total 24 events in 36 months (4.5%). Of the patients with HBP threshold increase, 5 patients had a previously implanted right ventricular backup lead, 4 patients had non-selective HBP with myocardial capture serving as a "back-up", in 4 patients a new right ventricular lead was implanted and in one patient LBBAP was performed. There were no clinical events due to threshold increase or loss of HBP capture.

HBP implantation success rates of ≥ 95% can be achieved. Over 36 months there is a modest pacing threshold increase from 1.0 to 1.6V/1.0 ms. This threshold increase did not cause any clinically relevant events in our patient cohort.