The purpose of this study is to investigate the cardiac electrical characteristics in different pacing outputs and body positions in LBB area pacing (LBBAP), from which the findings may help to develop and support data validation of a novel algorithm for LBB capture determination for LBBAP.

Among LBB area pacing (LBBAP), it has been reported that left ventricular (LV) septal pacing (LVSP), which refers to a pacing approach that only captures the LV septal myocardium, produces homogeneous electrical propagation in the septum and leads to delayed LV lateral wall activation. Although large randomized trials are lacking, small observational studies have shown more preserved physiological ventricular depolarization, or superior electrical and mechanical synchrony of the LBB capture over LVSP.

During the implantation of a device, the most commonly used method to distinguish LVSP from the LBB capture is to pace with different pacing outputs. A transition will be found in the ECG morphology with changes in the LV activation time if the pacing capture threshold (PCT) of the local myocardium is different from that of the LBB (i.e., LBB-PCT), indicating a transition between capturing the LBB and LVSP without any LBB capture. So far, there is no systematic investigation on the EGM characteristics or correlation between ECG and EGM characteristics at different conduction system capture status. Findings from this study will help to better characterize EGM characteristics and to develop an optimal LBBAP modality to differentiate LBB capture.

Inclusion Criteria:

• Patients aged >=18 years
• Patients who are willing to provide Informed Consent
• Patients who have received LBBAP therapy >= 1 month for 1 to 4 months (including 1 and 4 month)
• Patients implanted with a single/dual-chamber pacemaker or a CRT-P with LBBAP lead connected to RV port
• Implanted device can provide at least 3-channel real-time intracardiac electrogram

Exclusion Criteria:

• Patients who are pregnant or have a plan for pregnancy during the study
• Patients who have medical conditions that would limit study participation
• Patients who were already enrolled in clinical trial(s) which would impact study participation

The study selected two study site in China. One is a Tertiary A hospital in Shanghai, and another is a cardiovascular specialty hospital in Zhejiang Province. Both the two sites locate in the south east of China. This study will enroll 70 subjects who meet all the inclusion and exclusion criteria from the patients who have received LBBAP therapies from the two hospitals.