B-PO04-033 THE PACING SITE IS CLOSER TO THE LEFT VENTRICULAR SEPTAL ENDOCARDIUM DURING LEFT BUNDLE BRANCH PACING THAN DURING LEFT VENTRICULAR SEPTAL PACING

Abstract

Left bundle branch pacing (LBBP) using a transventricular septal method has emerged as an effective approach to physiological pacing. However, differentiating between LBBP and left ventricular (LV) septal pacing (LVSP) remains a challenge because both modalities generate narrow paced QRS complexes, which present with a right bundle branch block (RBBB) electrocardiographic pattern. To compare the distance between the pacing lead tip and LV septal endocardium on echocardiography between patients who underwent successful LBBP and LVSP. Twenty-five consecutive patients (74.2±9.2 y, 60% male) with traditional indications for permanent cardiac pacing were included in this study. Unipolar pacing from final sites generated narrow QRS complexes with a RBBB pattern in all patients. Left bundle branch (LBB) potentials were recorded at the final pacing sites in the 17 patients who constituted the LBBP group. In the 8 patients in the LVSP group, LBB potentials were absent at the final pacing sites and the R-wave peak time in lead V5 was consistent at high and low outputs. Medtronic SelectSecure® 3830 pacing leads were used in all patients. After the procedures, a physician who was blinded to the group selection performed echocardiographic measurements of the distance between the lead tip and LV septal endocardium in all patients. The paced QRS duration was comparable between LBBP and LVSP group (102.4±15.9 ms vs. 113.7±21.1 ms, P=0.264). In the LBBP group, the interval from LBB potential to the onset of the QRS was 31.4±10.0 ms. The distance between the lead tip and LV septal endocardium was 0.4±0.6 mm in the LBBP group and 2.6±2.1mm in the LVSP group during the diastolic phase (P=0.004). During the systolic phase, the distance was 0.6±0.9 mm in the LBBP patients and 4.0±3.6 mm in the LVSP patients (P=0.004). The sensing amplitude identified during follow-up was 16.14±3.83 mV in the LBBP group and 8.98±1.94 mV in the LVSP group (P=0.001). The landing zone of the lead tip was much closer to the LV septal endocardium in patients who underwent LBBP than in those who underwent LVSP. Our study highlights the need for real-time intraprocedural monitoring of the distance between the lead tip and the LV septal endocardium in patients who undergo LBBP.