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.