His Bundle pacing can normalize ventricular activation but can it also actually reconstitute native intrinsic conduction ?

His Bundle pacing  (HBP) has been known for years to be capable of normalizing bundle branch blocks. By normalizing I mean that the QRS while the patient is being paced becomes normal with Selective HBP and nearly so with non selective HBP. By reconstitution I mean that the QRS remains normal after HBP is turned off.  Reconstitution  is what authors of 2 case reports document in a article in Heart Rhythm Case Reports.

Dr FM Ezzeddine at al  (1) report two case in which patients with long standing conduction defects were implanted with His leads and after several months of treatment with His bundle CRT  were noted on routine testing  to have resolution of their conduction defects.One patient who had an av block and LBBB had resolution of the AV block while the LBBB continued and the second patient had restoration of normal ventricular conduction no longer having an LBBB pattern. Both patients experienced a significant resolution of their heart failure symptoms when His bundle paced CRT was begun.

Quoting the authors with my underlining.

"His Bundle pacing can restore native intrinsic conduction in some cases after years of chronic conduction block". ..    this demonstrates new theoretical benefits of HBP , the ability to promote conduction down the native pathways that were previously non-conducting." 

 What I  believe  the authors are proposing is that  His bundle pacing had somehow brought about  electrical remodeling  leading to a condition in which pacing was no longer needed to bypass or override whatever specific type of conduction defect the patient had experienced. They consider mechanisms such as Wedensky facilitation which refers to an impulse arriving at a blocked zone and increasing the excitability of tissue beyond the block. Other electrophysiologic speculations are offered.

There have reports of exercise induced LBBB and intermittent rate related LBBB but the authors believe these are the first reports of long standing conduction defects that recovered native conduction following continuous His bundle pacing.

On page 412 of Serge Barold's illustrated guide to pacemakers and resynchronizatio (2)n  the authors suggest there is value to periodically "expose " the underlying spontaneous EKG. This was said in the context of followup on bi-ventricular pacing but perhaps Ezzeddine's paper offers a reason to do that for patients with LBBB who are being His bundle paced.   

 

1) Ezzeddine, FM et al Reconstitution of native intrinsic conduction in patients with chronic conduction block with His bundle pacing. Heart Rhythm Case Reports.2021 1-5,  https;//doi/org/10.1016/j.hrcr,2021.03.006

note: The same cases were presented as a poster, at the JACC meting march 20,2018 by Dr. Ezzeddine

2) Cardiac Pacemakers and Resynchronization , step by step  An Illustrated guide. Second Edition,

Bakrold,SS, Stroobandt, RX adn Sinnaeve, AF