Bundle Branch Block Pattern Resolution in Non-Selective His Bundle Pacing: Effect of Programmed AV Delays

Abstract

We have reported that non-selective but not selective His-bundle pacing (HBP) resolves bundle branch block (BBB) pattern. Characterized by ventricular pre-excitation, the mechanism by which nonselective-HBP resolves BBB is unknown. As A-V delays may determine both duration and timing of ventricular pre-excitation, it was hypothesized that an analysis of P-wave to HBP interval in relation to P-wave to His-bundle electrogram (HBE), may yield further insights into resolution of BBB pattern in NS-HBP. Methods: In 27 patients with RBBB+LAD (n=11) and LBBB (n=16), QRS parameters at AV delays resulting in P-HBP interval P-HBE. Results: At P-33 HBP< P-HBE, the pre-excitation duration was longest (63±13ms), and a more normal pre-excited complex replaced the RBBB, LAD, or LBBB pattern. In addition, the QRS-voltage in L1 was restored (LAD and LBBB), QRS-axis normalized (LAD), ventricular activation times decreased (LBBB) and rightward delay (S wave in L1) resolved (RBBB) (p<0.01). At longer A-V delays with P-HBP interval prolonging incrementally beyond P-HBE interval, underlying BBB emerged progressively, and correlated with both delayed pre-excitation and decrease in pre-excitation duration. Conclusion: The resolution of BBB pattern is associated with maximal pre-excitation in NS-HBP. Delayed ventricular pre-excitation and decreased pre-42 excitation duration, caused by with longer AV delays, result in progressive fusion complexes with increasing BBB pattern. Thus, our data is most consistent with a bundle branch pattern being replaced by a more normal pre-excited QRS pattern, and less consistent with correction of BBB itself.