It was through a tweet in March 2017 that I realized that His bundle pacing was gaining momentum. I was surprised and frankly a little piqued that I was unaware of this promising technique. How difficult could it be, I asked — after all, we have been recording the His bundle electrogram for decades! After researching the basic requirements for His pacing, we acquired C315 guide catheters and model 3830 pacing leads (Medtronic). What followed was a humbling experience. Overnight, our procedure time went from around 20 minutes for a dual-chamber pacemaker to over 90 minutes for a His pacing device.
His pacing wreaked havoc with our scheduling as we struggled to become more efficient. Interestingly, achieving a narrow paced QRS was somehow deeply satisfying to every member of the team, and that appeared to be reward enough.
Very early on, we came to realize the potential of His pacing and decided that it was superior not only to right ventricular pacing, but perhaps superior to pacing epicardially via the coronary sinus. We based our reasoning on the fact that normal activation of the left ventricle is a complex endocardial to epicardial activation, which results in a spiral, twisting, and squeezing contraction, that may be best emulated by engaging the His bundle itself. As such, we switched almost exclusively to His bundle pacing. A right ventricular lead (or rarely, a coronary sinus lead) was placed only if a backup lead was indicated (e.g., if His bundle ablation was contemplated). Patients referred for cardiac synchronization therapy (CRT) received a His bundle lead. The response from our patients was most gratifying. Soon, our heart failure service was referring CRT non-responders for His bundle upgrade, and we have not looked back.
Our experience has taught us a few lessons. First, His bundle pacing is a team effort. Everyone in the EP lab is involved and, I suspect, there is an unspoken competition as to who spots the His electrogram first. To map in the correct area, it is helpful to locate the coronary sinus as the His bundle is positioned anterior and somewhat superior to it. This relationship is likely to be preserved even when the right atrial anatomy is altered. The His bundle electrogram and lead I or II are best displayed together. The normal paced QRS axis and shorter ventricular activation time are best observed in these leads. In patients with atrial fibrillation, the His bundle electrogram will be a constant signal preceding the QRS in otherwise chaotic signals of atrial fibrillation. The His bundle electrogram is typically seen fleetingly at first, primarily because one tends to make larger guide catheter movements trying to locate it. Once spotted, it helps to save the fluoroscopy image. Then, mapping is best done with micromovements of the guide catheter, pushing it superior, withdrawing it inferior, and turning it clockwise for anterior and counterclockwise for posterior locations. In fixing the His bundle lead, it helps to have another person rotate the lead while you hold the guide catheter steady. (Video 1)
Starting out, we anticipated quite a few challenges. These included the fear of complete heart block, His lead dislodgement, small sensed R waves, or high His pacing thresholds. The concerns turned out to be quite manageable. For example, we learned that if a lead position caused a complete heart block, it was a good site to fix the lead, as it typically results in a narrow paced QRS complex. In our experience, His lead dislodgements appear to be no more common than with an RV lead. As for R wave amplitude, we will accept a 2 mV value, which is in the range as a P wave value, and we have not had sensing problems. Finally, if the goal of achieving a narrow QRS requires an additional volt or two for optimal pacing, then so be it. The need for longer battery life is easily addressed by current technology.
We reported some of our experience at HRS 2019, in particular, our observation that acute and chronic conduction blocks were voltage dependent and that optimal QRS narrowing required higher pacing voltage. We have also presented our experience in patients with atrial fibrillation and severe pulmonary disease and/or congestive heart failure. These patients had frequent admissions with rapid heart rates. Following His bundle pacing and proximal His bundle ablation, there was a remarkable decrease in hospital admissions.
In patients with normal QRS, both RV pacing and biventricular pacing increases mortality. In our experience, while His bundle pacing has yet to prove its compliance of the Hippocratic injunction primum non nocere (first, do no harm), it does show promise for primum minus nocere (first, do less harm).
Disclosure: The author has no conflicts of interest to report regarding the content herein.