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 V 1 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 V 1 was significantly shorter during LBBAP than during native RBBB (51 ± 12 ms vs 85 ± 19 ms, p < 0.001). LBB potentials were recorded in 66.1% (37/56) of the LBBAP patients. No significant differences in ECG characteristics were found between LBBAP with and without recorded LBB potentials. The presence of bundle branch block during LBBAP significantly prolonged QRS duration, R wave peak time, and terminal R’ wave duration in lead V 1 . Conclusion LBBAP‐ECG patterns are characterized by a shorter terminal R’ wave duration in lead V 1 compared with that of native RBBB configurations. Bundle branch conduction integrity has an impact on ECG characteristics during LBBAP.