The electrophysiological characteristics and meanings in left bundle branch pacing based on unipolar and bipolar pacing.

Left bundle branch pacing (LBBP) is considered as an innovative physiologic pacing form because of lower thresholds compared with His bundle pacing and can partially resolve distal bundle disease (1). Our group had reported a novel LBBP lead implantation procedure guided by electrocardiogram (ECG) and electrogram (EGM) morphology under beat-to-beat monitoring, and found the isoelectric interval was a safe and precise endpoint for implantation, and was feasible in 87.8% (2). Few studies described the ECG and EGM characteristics of bipolar pacing due to the inaccuracy of selective left bundle branch pacing (SLBBP). This is the first case to report the electrophysiological characteristics of four unipolar or bipolar pacing modes and try to analyze the potential mechanism of different ECG and EGM morphology.