Sex-Based Differences in Left Bundle Branch Capture During Left Bundle Branch Area Pacing.

OBJECTIVE: To identify sex-based differences in meeting left bundle branch (LBB) capture criteria on postimplant ECGs. BACKGROUND: Despite differences in QRS duration (QRSd) between males and females, no sex-based criteria have been established for defining LBB capture during LBB area pacing (LBBAP). METHODS: Patients aged >18 y.o. with a pacing indication and dual-chamber LBBAP pacemaker implantation from 2020 to 2023 were studied. Baseline and postoperative day 1 (POD1) ECGs were assessed for electrical dyssynchrony (QRS-area, sum-absolute integral of QRS-T (SAI QRS-T)), with LBB capture defined based on R-wave peak times (RWPT) per the EHRA 2023 Consensus algorithm. RESULTS: The cohort included 222 patients (143 males/79 females, age 74.5±1.1 years, LVEF 53.7±0.4%). Baseline QRSd was significantly shorter among females than males (median 122 ms [90,134] vs 126 ms [102,146]; p = 0.018). LBB capture criteria were met in 83 (58.0%) male and 56 (70.9%) female patients (p = 0.058). Baseline and POD1 dyssynchrony were similar between sexes. However, RWPTs measured in leads V6/I/aVL were ∼7 ms shorter in females than males (V6-RWPT: 66.3 ± 1.6 ms vs. 73.7 ± 1.4 ms, p = 0.0008). Adjusting V6-RWPT up by 7 ms in females resulted in 7/56 patients (12.5%) no longer meeting LBB capture criteria. Significant differences were eliminated when normalizing RWPTs to size parameters (LV size, height, body surface area (BSA)), with no significant correlation between V6-RWPT and size. CONCLUSIONS: Females with LBB capture exhibit shorter V6-RWPTs despite similar measures of electrical dyssynchrony. This difference disappears when normalizing for the smaller size of female hearts. Additional studies are warranted to establish sex-specific LBB capture criteria. GRAPHICAL ABSTRACT: Despite innate differences in QRS duration between males and females, no recommendations have been established to assess for left bundle branch (LBB) capture across different sexes in patients undergoing LBB area pacing (LBBAP). To this end, we performed a retrospective study analyzing postimplant ECGs from 222 patients (143 males/79 females). R-wave peak times (RWPTs), traditionally used to identify LBB capture, were noted to be ∼7 ms shorter in females vs. males, with the differences resolved when accounting for smaller size of female hearts despite no correlation between RWPT and body/heart size. These results argue towards establishing sex-based cutoffs for LBB capture.

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