Achievement rate and learning curve of left bundle branch capture in left bundle branch area pacing procedure performed to demonstrate output-dependent QRS transition

Introduction: Recently, output-dependent QRS transition was reported to be required to confirm left bundle branch (LBB) capture in LBB area pacing (LBBAP) procedure. This study aimed to evaluate the achievement rate and the learning curve of LBB capture in LBBAP procedure performed with the goal of demonstrating output-dependent QRS transition, and investigate predictors of LBB capture.

Methods and results: The LBBAP procedure was performed in 126 patients with bradyarrhythmia. LBB capture was defined as a demonstration of output-dependent QRS transition. The following pacing definitions were used for evaluation: (1) LBBAP, which met the previously reported LBBAP criteria, (2) LBB pacing (LBBP), LBB capture was confirmed, and (3) available LBBP, LBB threshold was clinically usable (<3 V at 0.4 ms). The learning curve was evaluated by division into three time-periods. The achievement rates of LBBAP, LBBP, and available LBBP were 88.1%, 41.2%, and 35.7%, respectively. The achievement rates of all three pacing definitions significantly increased with experience (p < .01), but the achievement rate of available LBBP was still 50% in the third period. As predictors of LBB capture, the interval between LBB-Purkinje potential and QRS onset ≥22 ms had high specificity of 98.3%, while R wave peak time in V6 < 68 ms had insufficient sensitivity of 79% and specificity of 68%.

Conclusion: Even if LBB capture was aimed in LBBAP procedure, it was not easy to achieve, and there was a clear learning curve. Much of LBBAP may be left ventricular septal pacing that does not capture LBB.