Left bundle fascicular versus left bundle trunk pacing: a comparison of their electrical synchrony parameters
Authors: Estevez Paniagua A , Briongos Figuero S , Sanchez Hernandez A , Munoz Aguilera R 
Published: May 2024

Abstract

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 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 in the frontal axis. We compared them regarding procedure, LBBP criteria and electrical synchrony parameters.

Results
309 patients with LBBAP attempt were analysed, with 290 successful cases. Among them, 223 were considered LBBP. 25 cases without a proper ECG tracing in the frontal leads were excluded from the final analysis.
173 patients with LBFP were compared to 25 patients with LBTP. There were not significant differences in the baseline characteristics, but the native QRS width was higher in the LBFP group (119.2±31.4 ms vs 103.2±20.5 ms; p=0.014). Regarding the procedural duration, there was not any significant difference. 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, left septal (LSFP) and posterior (LPFP) fascicles were significantly more prevalent than left anterior (LAFP) in LBFP (46.8%, 41.0% and 12.2% respectively). Regarding the baseline characteristics, the procedural performance and the electrical synchrony parameters, there were not significant differences among the LBFP subgroups. Only aVL-RWPT was longer when the posterior fascicle was paced, and shorter in LAFP (84.7±13.3 ms vs 64.9±15.1 ms; p&lt;0.001). The consecution of LSFP was more frequent with lumenless leads (97.5% vs 83.1% vs 81.0%, p=0.006). Attending to the LBBP criteria, transition criteria were more frequent in LSFP (71.6% vs 53.2%; p=0.039), along with selective capture (29.6% vs 16.3%%; p=0.042), and transition during pacing manoeuvres (82.8% vs 69.2% vs 40.0%; p=0.013).

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, without significant differences among the LBFP subgroups. The recognition of the different paced QRS morphologies in the frontal axis, along with the analysis of the Purkinje potentials, arise as important tools to fully understand the whole map of LBBAP.Left bundle branch area sites of pacingProcedural and LBBP characteristics