Electrocardiographic morphology during left bundle branch area pacing: Characteristics, underlying mechanisms, and clinical implications

Aims In this study, we investigated the characteristics and underlying mechanisms of the electrocardiographic (ECG) morphology during left bundle branch area pacing (LBBAP), which have not been systematically described. Methods Patients with indications for permanent cardiac pacing underwent LBBAP attempts. The ECGs of patients with confirmed left bundle branch (LBB) capture were compared with those of individuals with right bundle branch block (RBBB) on 12‐lead ECG. Intracardiac electrograms recorded during implantation were analyzed in all patients who underwent pacing. Results LBBAP was successfully achieved in 87.5% (56/64) of patients. The QRS morphologies in lead V1 during LBBAP, which typically demonstrated Qr (60.7%), qR (19.6%), rSR’ (7.1%), or QS (12.5%) patterns, differed from those of native RBBB, which featured rsR’ (57.5%), M shape (23.7%), or monophasic R patterns (18.7%). The terminal R' wave duration in lead V1 was significantly shorter during LBBAP than during native RBBB (51 ± 12 ms vs 85 ± 19 ms, p