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

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.

The purpose of this study was to evaluate the presence of output-dependent QRS transition and capture thresholds of the LBB and left ventricular septal myocardium immediately and up to 1 year after the LBBAP procedure.

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) and after 3 days (POD-3), 6 months (POD-180), and 1 year (POD-360).

Output-dependent QRS transition persisted in 64 patients (88%) on POD-360, from among the 73 patients with output-dependent QRS transition on POD-0. In contrast, 55 of 56 patients without QRS transition on POD-0 (98%) did not exhibit QRS transition thereafter. LBB thresholds were slightly elevated on POD-360, albeit without statistical significance, compared with those on POD-0 (1.22 ± 1.00 V vs 1.43 ± 1.29 V at 0.4 ms; P = .26). The LBB thresholds increased by ≥1.5 V in 7 patients (11%). 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. Left ventricular septal thresholds were similar on POD-0 and POD-360 (0.81 ± 0.36 V vs 0.83 ± 0.24 V; P > .99) and did not increase by ≥1.5 V in any patient.

Output-dependent QRS transitions were highly reproducible after implantation. Furthermore, LBB thresholds remained stable in most cases during the first postoperative year.