Definition of successful HBP or LBBAP implant
HBP was defined as selective or non-selective capture as previoulsy described17. LBBAP was categorized as left bundle branch pacing (LBBP) or left ventricular septal pacing (LVSP). LBBP was defined according to the criteria described by Huang et al.16 including: 1. RBBB pattern paced morphology; 2. Visualization of LBB potential; 3. Left ventricular activation time (LVAT) short and constant at high (5V) and low output (1V), or abrupt shortening at high output; 4. Transition from nonselective to selective LBBP during threshold testing. LBBP was considered present when at least 3 or more of these criteria were fullfilled. When LBBP criteria were not met but a deep septal position of the lead was evidenced with contrast (Supplementary video 1) and significant reduction in the final paced QRS width or a final paced QRS ≤130 ms was obtained, the implant was considered as LVSP