Upgrade procedure
The 4.1F 3830 (SelectSecure, Medtronic, Minneapolis, MN) pacing lead was delivered using the C315HIS (Medtronic, Minneapolis, MN) sheath. His bundle electrograms were mapped in a unipolar configuration and recorded on the recording system (Prucka Cardiolab, GE Healthcare, Waukesha, WI). To locate the optimal site for the His bundle lead, the sheathes and leads were delivered to the ventricular end for the distal HBP/LBBP, and the pacing rate was decreased to 30 bpm for an escape rhythm. If no his electrogram was observed, pace mapping was conducted to identify a site with evidence for His bundle capture. His bundle pacing was acceptable when capture threshold was lower than 2.0V/1.0ms.For the patients with third-degree atrioventricular block (III°AVB) or ventricular pacing dependent, right ventricular backup pacing was retained if threshold of his bundle pacing is higher than 2.0v/0.5ms. LBBP would be further performed when HBP failed.