Durability of output-dependent QRS transition and left bundle branch capture in left bundle branch area pacing.

Background: Although output-dependent QRS transition is a specific indicator that confirms left bundle branch (LBB) capture during left bundle branch area pacing (LBBAP), its durability remains unclear.
Objective: To evaluate the presence of output-dependent QRS transition and capture thresholds of the LBB and left ventricular septal myocardium (LVS) immediately and up to 1 year after the LBBAP procedure.
Methods: We enrolled 129 patients with successful LBBAP who were available for 1-year follow-up postoperatively. Threshold testing was performed immediately after LBBAP on postoperative day 0 (POD-0), after three days (POD-3), 6 months (POD-180), and 1 year (POD-360).
Results: Output-dependent QRS transition persisted in 64 (88%) patients on POD-360, from amongst the 73 patients with output-dependent QRS transition on POD-0. In contrast, 55 (98%) of 56 patients without QRS transition on POD-0 did not exhibit QRS transition thereafter. LBB thresholds were slightly elevated on POD-360, albeit without statistical significance, compared to those on POD-0 (1.22 ± 1.00 vs. 1.43 ± 1.29 V at 0.4 ms, p=0.26). The LBB thresholds increased by ≥1.5 V in 7 (11%) patients. However, in 93% of patients with an LBB threshold of ≤2.5 V on POD-0, LBB capture was maintained at 2.5 V on POD-360. LVS thresholds were similar on POD-0 and POD-360 (0.81 ± 0.36 vs. 0.83 ± 0.24 V, p=1.0), and did not increase by ≥1.5 V in any patient.
Conclusion: Output-dependent QRS transitions were highly reproducible after implantation. Furthermore, LBB thresholds remained stable in most cases during the first postoperative year.
(Copyright © 2024. Published by Elsevier Inc.)