The goal of this observational study is to investigate the changes of LBB EGM during daily activities and overdrive pacing at the time of peri-implantation and up to 6-month follow-ups of ICD/CRT-D patients. The main question it aims to answer is:

• Does the LBBP lead can provide accurate, stable, and valid EGM for ICD/CRT-D sensing and detection of ventricular tachyarrhythmia events? In each patient intracardiac EGMs of LBBP lead will be collected by ambulatory Holter monitor at the time of peri-implantation and up to 6-month follow-up. EGM collection will be collected at resting and walking conditions and overdrive pacing.

Inclusion Criteria:

• Patients aged >=18 yrs.
• Patients indicated for ICD or CRT-D (primary or secondary prevention)
• Patients who recently (<=30 days) received ICD/CRT-D implantation with LBBP
• Patients' EGM can be digitally recorded
• Patients are willing to participate in the study and provide signed informed consent

Exclusion Criteria:

• Patients received CIED upgrade or replacement with old pacing leads
• Patients are pregnant
• Patients participate in another study that will confound this study

The study selected two study site in China. One is a Tertiary A hospital in Zhejiang Province, and another is a hospital in Shanghai. Both of the two sites locate in south east of China. This study will enroll around 50 subjects who meet the inclusion and exclusion criteria from the ICD or CRT-D patients who have received LBBAP in the two hospitals.