Is the pacing site closer to the left ventricular septal endocardium in left bundle branch pacing or in left ventricular septal pacing?

Abstract

Distinguishing between left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP) is challenging. This study aimed to compare the echocardiographic distance from the pacing lead tip to the left ventricular (LV) septal endocardium between patients who underwent LBBP and those who underwent LVSP successfully. Fifty-nine consecutive patients (age 71.9 ± 12.0years, 35.6% male) with traditional indications for permanent cardiac pacing were included (LBBP group, n = 46; LVSP group, n = 13). Unipolar pacing from the final pacing sites generated narrow QRS complexes with a right bundle branch block pattern in all patients. After the procedure, a physician blinded to the group allocation performed echocardiographic measurements of the distance between the lead tip and the LV septal endocardium. The mean paced QRS duration was comparable between the LBBP group and the LVSP group (105.3 ± 15.6ms vs. 109.2 ± 9.6ms, P = 0.287). In the LBBP group, the interval from the left bundle branch potential to QRS onset was 28.7 ± 9.0ms. During diastole, the mean distance between the lead tip and the LV septal endocardium was 0.6 ± 0.9mm in the LBBP group and 3.0 ± 1.6mm in the LVSP group (P < 0.001). During systole, the distance was 1.5 ± 1.4mm in the LBBP group and 4.3 ± 2.6mm in the LVSP group (P < 0.001). The landing zone of the lead tip was closer to the LV septal endocardium in the patients who underwent LBBP. There is a need for real-time intraprocedural monitoring of the distance between the lead tip and the LV septal endocardium when performing LBBP.