An individualized criterion for left bundle branch capture in patients with a narrow QRS complex

Left bundle branch (LBB) pacing (LBBP) is a physiological pacing; however, the accuracy of current electrocardiographic criteria for LBBP remains inadequate.

The purpose of this study was to establish a novel individualized criterion to improve the accuracy of LBBP determination in patients with a narrow QRS complex.

Patients in whom both LBBP and left ventricular septal pacing (LVSP) were acquired during operation were enrolled. LBB conduction time (LBBCT) was measured from LBB potential (LBB_po) to intrinsic QRS onset. LBB_po-V₆RWPT, Native-V₆RWPT, and Paced-V₆RWPT were respectively measured from LBB_po, intrinsic QRS onset, and stimulus to R-wave peak in V₆. ΔV₆RWPT was the difference value between Paced-V₆RWPT and Native-V₆RWPT. The accuracy of ΔV₆RWPT criterion for determining LBBP was evaluated.

In all 71 enrolled patients, ΔV₆RWPT was <30 ms during LBBP (21.3 ± 4.6 ms; range 9.3-28.3 ms) but was >30 ms during LVSP (38.5 ± 4.6 ms; range 31.1-47.0 ms). The probability distribution of ΔV₆RWPT was well separated between LBBP and LVSP. Sensitivity and specificity of the novel criterion of "ΔV₆RWPT <30 ms" for determining LBBP both were 100%. However, the optimal cutoff value of Paced-V₆RWPT for validation of LBBP was 64.2 ms, and sensitivity and specificity were 84.5% and 97.2%, respectively. Paced-V₆RWPT during LBBP was equivalent to LBB_po-V₆RWPT in all patients. There was a strong linear correlation between Native-V₆RWPT and LBB_po-V₆RWPT (r = 0.796; P <.001).

ΔV₆RWPT could be an accurate individualized criterion for determining LBB capture with high sensitivity and specificity and was superior over the fixed Paced-V₆RWPT criterion.