Effects of LBBAP Pacing-Site Position under a Modelled Proximal LBBB: A 24-Model Electrophysiological Simulation Study

Left bundle branch area pacing (LBBAP) may recruit the distal left-sided conduction system, but the electrical effect of pacing-site position along the left bundle branch (LBB) remains incompletely defined. We evaluated this effect in 24 four-chamber virtual heart anatomies using a Reaction-Eikonal finite-element model with rule-based myocardial fibres and algorithmically generated His-Purkinje networks. A modelled proximal His to-LBB disconnection preserved the distal LBB-Purkinje network while interrupting its proximal connection. Six conditions were simulated in each anatomy: a sinoatrial-node (SAN)-initiated left bundle branch block (LBBB) control, right ventricular apical pacing, right ventricular outflow-tract pacing and a modelled non-selective LBB capture configuration at proximal, nominal and distal positions. The primary outcome was BiV_TAT95, the 95th percentile of activation times across left-ventricular, right ventricular and interventricular-septal nodes. The control-versus-paced analysis used a common simulation-clock origin and was interpreted as contextual benchmarking, whereas the positional analysis used matched direct ventricular stimulation. In the matched positional analysis, median BiV_TAT95 was 104.5, 93.5 and 88.5 ms for proximal, nominal and distal LBBAP, respectively (Friedman chi-square = 48.000, P < 0.001, Kendall's W = 1.000); every anatomy followed distal < nominal < proximal. In three selected anatomies, a 20% decrease or increase in the prescribed myocardial conduction speeds altered absolute activation times but preserved this ordering in all nine anatomy-by-speed combinations. Under the tested homogeneous substrate and modelled non-selective capture configuration, the distal tested position produced the lowest simulated BiV_TAT95; this does not imply superiority for every activation metric. This conditional prediction requires validation against patient-specific electrical data.