His-bundle Pacing: Promise for the Future

Pugazhendhi Vijayaraman; Sergio Richter


Europace. 2019;21(5):686-687. 

Conventional right ventricular pacing has been the cornerstone of bradycardia therapy for the last six decades. Despite very early description of the adverse haemodynamic effects of ventricular pacing by Wiggers[1] in 1925, the deleterious consequences of right ventricular pacing have only recently been fully recognized. Direct His-bundle pacing (HBP) reproducing native physiological ventricular activation was first described by Scherlag et al.[2] in 1967 in open-chest surgery dogs utilizing plunge electrodes. The feasibility of permanent HBP in humans was first demonstrated by Deshmukh et al.[3] in 2000, in patients with chronic atrial fibrillation undergoing atrioventricular node ablation, using conventional stylet-driven leads. In the next decade, several investigators were able to reproduce the clinical feasibility of permanent HBP without wider adoption of this technique. Challenging implant procedure, lower success rates, need for a mapping electrophysiology catheter, back-up ventricular pacing lead, higher pacing thresholds, and shortened device longevity were major factors limiting the acceptability of HBP. In 2015, the feasibility and safety of permanent HBP without a back-up ventricular pacing lead was reported by Sharma et al.[4] Additionally, this study demonstrated that the procedural duration was only slightly longer than conventional right ventricular pacing with comparable fluoroscopy duration. In this study, the mean His-bundle capture thresholds were reported to be 1.35 V @ 0.5 ms, significantly lower than in the original cohort (2.4 V @ 0.5 ms) of Deshmukh et al.[3] In a long-term follow-up, Vijayaraman et al.[5] showed that the mean HBP thresholds remained relatively stable at 1.62 V @ 0.5 ms at 5 years.

Su et al.[6] present their experience with HBP in a large series of patients over a 4-year period. The authors must be commended for their observations and improvisation to achieve higher success rates and lower pacing thresholds. During their first phase of HBP, the implant success rates were 77% comparable to that of Vijayaraman et al.[5] (80%). His capture thresholds were also similar (1.3 vs. 1.35 V) in these two groups. However, during the final phase, their implant success rates improved to 89.6%, similar to that in the Geisinger HBP registry in their subsequent series of 332 patients with success rates of 92%.[7] In addition to improving their implant success rates, the authors have demonstrated superior pacing outcomes by adding few procedural modifications. The acute His-bundle capture thresholds of 0.85 V @ 0.5 ms achieved during their final phase are the lowest reported compared with several recent reports on HBP. More importantly, the capture thresholds remained stable at 1.03 V @ 0.5 ms at 12-month follow-up, which is almost as good as ventricular myocardial capture thresholds achieved during traditional right ventricular pacing.

The authors' use of the dual lead method in order to improve implant success rates, aids in achieving a distal location in the His-bundle axis. This may allow for locating the pacing site beyond the site of conduction block in patients with intra-Hisian atrioventricular block and/or bundle branch block. In addition to achieving better pacing thresholds, a distal location provides better ventricular sensing parameters often resulting in non-selective His-bundle capture, eliminating the need for back-up ventricular pacing lead. Lastly, deeper fixation of the lead by additional rotations after the sheath is partially withdrawn also seems to have reduced the incidence of late threshold increases in their cohort of patients. In essence, the meticulous approach to HBP (dual-lead, distal and deeper) appears to have solved many of the impediments to wider adoption of HBP in clinical practice. In this series, the authors have used a dual-lead technique in approximately one-third of the patients studied. While the dual-lead method has increased the procedural success, it may be associated with higher cost, which may discourage new implanters from adopting permanent HBP.

Bhatt et al.[8] recently reported on their institutional experience with regards to HBP implant success, threshold increase and lead revision rates in 101 patients. The success rates varied from 56% in patients with complete heart block to 83% in its absence. Importantly, a rising threshold was noted in 30% of their patients, while 8% required lead revision. They also reported a learning curve with regards to pacing thresholds and lead revision rates. In this context, it is important to point out that only two operators performed HBP in the current study[6] (L.S. and W.H.) compared with five operators in the study reported by Bhatt et al.[8] Similarly, only three operators were involved in the Geisinger study[7] with very high operator experience among the two of them. Both Wenzhou and Geisinger studies report attempting HBP in all patients requiring permanent pacemaker implantations irrespective of the indication. These findings suggest that mastering of permanent HBP requires a larger volume and higher frequency to achieve the required learning curve.

In the last few years, HBP has been adopted by more physicians around the world in their clinical practice. Based on the limited published data and systematic review,[9]physiologic pacing utilizing HBP has now been incorporated into the 2018 AHA/ACC/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay.[10] HBP is recommended as a Class IIa-B indication in patients with atrioventricular block who have an indication for permanent pacing with a left ventricular ejection fraction between 36% and 50% and are expected to require ventricular pacing more than 40% of the time. In patients with atrioventricular block at the level of the atrioventricular node who have an indication for permanent pacing, HBP may be considered to maintain physiologic ventricular activation (Class IIb-B). Nonetheless, HBP is currently utilized in less than 2% of the pacemakers implanted worldwide. While the benefits of permanent HBP are manifold (maintaining physiologic activation of both ventricles, prevention of pacing induced cardiomyopathy, restoration of cardiac synchrony in patients with cardiomyopathy, and ventricular dyssynchrony), further research and innovation is necessary before HBP can become the pacing mode of choice for every patient and implanting physician.[11] While experienced operators in select few institutions can achieve high degree of success, excellent thresholds and low lead revision rates, it needs to be replicated by more physicians globally. Standardizing the procedure, improvement in delivery tools, multiple choices of leads for specific pathology and appropriate devices with ability to deliver higher current and acceptable longevity is necessary to achieve the goal of physiologic pacing for everyone. In this regard, studies like this are an excellent step in the right direction.