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Monday, June 25, 2018

Bundle of His Pacing an overnight game changer fifty years in the making may have reached tipping point

Benjamin J. Scherlag,PhD, is credited as the first person to demonstrate an intra cardiac tracing of  His Bundle (HB) electrical activity. In1967, he demonstrated ventricular pacing from the bundle of His.

In 1970, OS Narula and Scherlag demonstrated the feasibility of temporary HB pacing in humans.

 In a 1978  article in Circulation, Scherlag,El-Sherif,Lazzara and others presented clinical and experimental data demonstrating the normalization of bundle branch blocks  ( right and left) with HB pacing.

Thirty years after Narula's work, Deshmukh's 2000 publication reported his experience in placing    permanent His Bundle pacing leads in   18 patients with dilated cardiomyopathy,poorly rate controlled atrial fibrillation and narrow QRS complexes who  underwent AV node  ablation. He  later published a larger series with 3 1/2 year follow-up on patients with supra-Hisian AV block.Although results were encouraging, the time for more widespread use of HB pacing has not yet quite arrived. The procedure was thought  to be  too challenging and  commercially designed equipment which would facilitate the procedure was not yet available .

 It required   a separate mapping catheter and higher pacing thresholds and it was not clear  exactly what subset of patients would be benefited by this method to a degree greater than obtained by the simpler apical right ventricular pacing in regard to which data suggesting the harmful effect of RV pacing were not yet fully appreciated. So HB pacing was not perceived as being ready for prime time.

From 2006 through 2012 work from Kronborg from Denmark and Zanon and others from Italy   strengthened the case for more widespread application of HB pacing.In 2011 Zanon reported the experience from  multi-institutional data using the Medtronic Select Secure system describing 307 patients implanted in the His zone with 87 having direct HB pacing and 220 with indirect or "Para-Hissian" pacing.

Two important papers from the United States were published in 2015:

A series of 98 HB paced  patients was reported by electrophysiologists from the Geisinger Clinic.
 with a longer follow reported by the same group in 2017.Also Lustgarten reported on a cross over trial comparing Bi-ventricular pacing with HB pacing in patients  receiving Cardiac Resynchronization Therapy (CRT).

Both papers indicated that the procedure was less difficult than previously thought due in part to newer specially designed sheath and leads,required lower pacing thresholds than earlier reports and follow-up data regarding stability of leads was encouraging and left ventricular function improved at least as much brought about by Bi-V pacing. Further the Geisinger data , while not a randomized trial,indicated that long term follow-up showed no decrease in left ventricular function while a parallel group who had the standard right ventricular apical pacing did show  decreased left ventricular function  and a 22% incidence of pacing induced cardiomyopathy was reported.

In EP cardiology, as in most things, there are tradeoffs. The HB paced patients had , in the Geisinger data, twice as many lead revisions after five years( 6.7% vs 3%) and significantly more generator changes when compared with the RV paced group ( 9% vs 1%) . In additional the procedure time was slightly longer as were  fluoroscopy times.

The Geisinger HB registry data was updated and published in 2018.This article was one of  several recent articles describing experiences with HB pacing in a variety of clinical settings and we may have reached a "tipping point" in terms of EP Cardiologist's attitudes re HB pacing.

Francesco Zanon from Rovigo Italy ,an early adaptor of HB pacing, published data on 147 patients referred with a variety of PM indications and various types of bundle branch block. 80 % of patients experienced disappearance of the BBB . 90% of the  patients had effective HB pacing with a mean follow up of five years. He spoke of a "new philosophy of how we pace".

 One of the fathers of electrophysiology, Benjamin Scherlag,has called for a randomized trial comparing HB with BiV pacing for CRT and Dr. Kenneth Ellenbogen has also commented on the need for  RCTs and wrote an editorial suggesting that possibly HB pacing was the Holy Grail of  pacemaker therapy .

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