Left bundle fascicular versus left bundle trunk pacing: A comparison of their electrical synchrony parameters.

Background: Variation in human left bundle branch (LBB) anatomy has a significant effect on the sequence of left ventricular depolarization. However, little is known regarding the electrophysiological characteristics of pacing different LBB fascicles.

Objective: We aimed to analyse the different electrocardiographic characteristics of LBB pacing (LBBP) attending to the site of pacing at the LBB system.

Methods: In 200 consecutive patients with confirmed LBBP, we distinguished left bundle trunk capture (LBTP) from any LB fascicular pacing (LBFP) based on the presence of LB potentials and paced QRS morphologies. We compared them regarding procedure, LBBP criteria and electrical synchrony parameters.

Results: One hundred and seventy-three patients with LBFP were compared to 25 patients with LBTP. Left septal and posterior fascicles were significantly more prevalent than left anterior in LBFP (46.8 %, 41.0 % and 12.2 % respectively). QRS transition criteria (80.0 % vs 61.8 %; p = 0.077), selective LBBP (40.0 vs 21.5 %; p = 0.101), paced QRS width (110.3 ± 16.8 ms vs 115.4 ± 14.9 ms; p = 0.117), V6-RWPT (79.2 ± 10.7 ms vs 75.3 ± 9.7 ms; p = 0.068) and interpeak interval (42.5 ± 19.1 ms vs 45.7 ± 12.9 ms; p = 0.282) were not significantly different between LBTP and LBFP. All short-term complications occurred in LBFP, mainly driven by septal perforations (n = 23), without any difference in the pacing parameters. Among the LBFP subgroups, only aVL-RWPT was longer when the posterior fascicle was paced.

Conclusions: LBFP is much more prevalent than LBTP in unselected consecutive patients with LBBP. LBFP seems more feasible, and as good as LBTP in terms of electrical synchrony and pacing safety.