Determinants of baseline electrical performance in left bundle branch area pacing: a comprehensive multivariable analysis and its relationship with mid-term electrical evolution

Background

Electrical parameters during left bundle branch area pacing (LBBAP) vary at implant depending on patient substrate, conduction system status, and procedural characteristics. Understanding these determinants is essential to contextualize and interpret the mid- to long-term electrical evolution observed in LBBAP follow-up studies.

Objective

To identify independent clinical, anatomical, electrical, and procedural predictors of key LBBAP electrical parameters at implant.

Methods

Consecutive patients undergoing successful LBBAP for bradycardia pacing indication and preserved LVEF were studied. Baseline 12-lead ECG during ventricular pacing was used to measure V1-RWPT, V6-RWPT, inter-peak interval, and paced QRS duration (from spike and onset). Univariate and multivariate linear regressions identified independent predictors. Multivariate models included clinical factors, structural parameters, electrical substrate, and LBBAP characteristics (LBBP vs LVSP, transition phenomena, LBBP morphology, and presence of LBB potential). Findings were compared with the previously reported multivariate predictors of follow-up electrical deltas in the same cohort.

Results

In 149 patients, several independent determinants of baseline electrical behavior were identified (Table 1, Figure 1). LV end-diastolic diameter (LVEDD) independently predicted longer V1-RWPT (β=0.250, p=0.018), inter-peak interval (β=0.249, p=0.024), and paced QRS duration from spike (β=0.229, p=0.027) and onset (β=0.221, p=0.037), highlighting the structural influence on ventricular activation.

V6-RWPT showed the strongest predictive model (R²=0.400): shorter V6-RWPT was independently associated with septal perforation during implantation (β=–0.203, p=0.029), lower pacing threshold (β=0.235, p=0.011), and more physiological pacing phenotypes, with LBBP outperforming LVSP and the presence of transition phenomena providing the shortest V6-RWPT (β=–0.344, p<0.001). Likewise, left bundle trunk pacing yielded shorter V6-RWPT than left fascicular pacing (β=–0.242, p=0.012). Intrinsic depolarization characteristics also influenced baseline electrical performance: longer intrinsic QRS duration predicted wider paced QRS both from spike (β=0.550, p=0.015) and onset (β=0.537, p=0.020). Notably, although both LBBAP phenotype and LBBP phenotype independently predicted V6-RWPT, and LBBAP phenotype also predicted the inter-peak interval, none of these variables—together with the presence of LB potential—independently determined the global paced QRS duration. This finding also mirrors their lack of influence on mid-term QRS evolution observed in the companion analysis.

Conclusions

Overall, baseline global electrical performance was strongly determined by intrinsic anatomical (LVEDD) and electrical factors (QRS duration). Meanwhile, LBBAP characteristics mainly predicted V6RWPT, but showed a lack of influence on global ventricular depolarization, mirroring electrical mid-term evolution.Table 1.Multivariate analysisFigure 1.Forest-plot