Effect of selective His bundle pacing on ventricular fibrillation activation rates in rabbit hearts
Authors: Shah Ankur Rajiv , Khan Muhammad Shuja , Lange Matthias , White Annie , Dosdall Derek 
Published: June 2021

Background/significanceThe His‐Purkinje system is electrically active and influences activation patterns and rates during ventricular fibrillation (VF). Purkinje system is involved in maintaining VF and may contribute to defibrillation shock failure. This study investigates if the His‐Purkinje system could be paced to modulate rate or patterns of activation during VF.MethodSeven New Zealand rabbit hearts were explanted and perfused in a Langendorff setup. The His bundle (HB) was accessed from the right atrial septal wall by opening the right atrium. An 8×8 Ag/AgCL electrode array was placed by the anterior vertex of Koch's triangle. The HB was identified using a custom real‐time stimulation‐recording and signal processing system. The system used spatial derivatives to identify electrodes specifically over the HB. A separate silver wire was inserted in the ventricular myocardium (VM) of the right septal wall to stimulate the VM and detect ventricular cycle lengths. A 64‐channel basket catheter (Orion catheter, Boston Scientific Inc) was inserted through an opening made in left atrium through the mitral valve and into the left ventricle. VF was induced by 50 Hz pacing on the left ventricular free wall. During VF, the HB was paced at 80 and 95% of intrinsic HB cycle lengths. Both the HB and VM were paced at 80 and 95% of the intrinsic VM cycle lengths. Both HB and VM were stimulated during VF at 10× the amplitude of the diastolic stimulation threshold. While the VM and HB were being stimulated, left ventricular endocardial activations were recorded from the basket catheter electrodes.The left ventricular endocardial recordings were analyzed using a custom graphical user interface developed in MATLAB (Mathworks, Inc., MA, USA). Broken channels or channels not in contact with the endocardial wall were excluded from the analysis.ResultsData from 2 out of 7 animals were excluded from analysis as pacing at electrodes with HB potentials did not lead to capture of the HB. HB pacing at 80% or 95% of HB CL did not affect the VF. In 4 animals, when the HB was paced at 95% of VM cycle lengths, the left ventricular endocardial activation rate was higher than when VM was paced at 95% of VM cycle lengths. In 3 animals, when HB was paced at 80% of VM cycle length, the left ventricular endocardial activation rate was higher than when the VM was paced at 80% of VM cycle length.Conclusion and discussionHB paced at 80 or 95% of HB cycle length did not affect the underlying VF. HB paced at 80% or 95% of VM cycle length affected the underlying VF activation rate more than when VM was paced at 80% or 95% VM CL. The increase in ventricular activation rate suggests ventricular tissue is activated at the Purkinje endpoints of the His‐Purkinje system as a result of His bundle pacing.Support or Funding InformationNational Institutes of Health award number R01HL128752 to Dr. Derek DosdallThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.