Activation dispersion index as a novel ECG marker for assessing ventricular electrical synchrony: Left bundle branch area pacing versus right ventricular apical pacing in post-TAVI patients with high-grade atrioventricular block.

BACKGROUND

Permanent pacemaker implantation is required in approximately 10-25% of patients following transcatheter aortic valve implantation (TAVI) due to complete atrioventricular (AV) block. Conventional right ventricular apical (RVA) pacing is known to induce ventricular electrical dyssynchrony, potentially contributing to pacing-induced cardiomyopathy. Left bundle branch area pacing (LBBAP) has emerged as a physiological alternative by recruiting the native conduction system. However, objective electrocardiographic quantification of ventricular synchrony in this population remains underexplored.

OBJECTIVES

To evaluate and compare ventricular electrical synchrony between LBBAP and RVA pacing in post-TAVI patients using a novel ECG-based metric - the Activation Dispersion Index (ADI).

METHODS

This retrospective, single-center, comparative study included 101 patients who developed high-grade AV block following TAVI and underwent permanent pacemaker implantation (LBBAP: n = 53; RVA pacing: n = 48). Precordial R-wave peak times (RWPT) in leads V1-V6 were measured manually on 12‑lead ECGs using ImageJ software (3 repeated measurements per lead). ADI was defined in two forms: ADI-SD (standard deviation of V1-V6 RWPT values) and ADI-Range (maximum minus minimum RWPT). Pre-pacing (intrinsic rhythm during high-grade AV block) and post-pacing ECGs were analyzed. The primary endpoint was the change in ADI-SD (ΔADI-SD = pre - post). Inter-group comparison was performed using the Mann-Whitney U test; within-group pre-post comparisons used the Wilcoxon signed-rank test.

RESULTS

Baseline demographic and clinical characteristics were comparable between groups. Pre-pacing ADI-SD was numerically higher in the LBBAP group (15.3 ± 6.7 vs. 12.5 ± 6.7 ms; p = 0.018). Following pacemaker implantation, LBBAP produced a significant reduction in both ADI-SD (15.3 ± 6.7 to 11.9 ± 4.8 ms; p = 0.001) and ADI-Range (39.4 ± 16.3 to 31.0 ± 13.7 ms; p = 0.001). In contrast, RVA pacing resulted in no significant change in ADI-SD (12.5 ± 6.7 to 12.3 ± 6.0 ms; p = 0.939) or ADI-Range (p = 0.926). Post-pacing ADI values converged between groups (ADI-SD: 11.9 vs. 12.3 ms; p = 0.865). ΔADI-SD was significantly greater in the LBBAP group (3.4 ± 7.0 vs. 0.2 ± 8.8 ms; p = 0.028; Cliff's δ = 0.25; 95% CI for mean difference: 0.11 to 6.35 ms). Post-pacing QRS duration was significantly shorter in the LBBAP group (107.8 ± 22.0 vs. 147.4 ± 19.2 ms; mean difference - 39.6 ms [95% CI -47.6 to -31.6 ms]; p < 0.001; Cliff's δ = -0.81), and within the LBBAP group, shorter post-pacing QRS duration correlated with greater ΔADI-SD (Spearman ρ = -0.34, p = 0.013).

CONCLUSIONS

LBBAP significantly reduces ECG-derived ventricular activation dispersion in post-TAVI patients with high-grade AV block, as quantified by the Activation Dispersion Index. RVA pacing does not alter ADI, suggesting persistence of electrical dyssynchrony. ADI represents a simple, reproducible, and non-invasive method for assessing ventricular electrical synchrony and may serve as a surrogate marker for pacing-induced cardiomyopathy risk stratification.