Left Bundle Branch Pacing Impact on QRS Amplitude in Different Pacing Voltages.

Abstract

Background: Left bundle branch pacing (LBBP) emerged as a novel physiological pacing modality that improves clinical outcomes. This study aimed to explore the impact of LBBP on QRS wave amplitude (RWA).

Methods: This prospective observational study included patients with complete left bundle branch block (CLBBB) and cardiac resynchronization therapy (CRT) indication, as well as patients with QRSd < 120 ms and pacemaker indication. During the procedure, when the LBBP lead reached the target site, 12-lead ECGs at baseline and 1, 2, 3, 4, and 5 times the pacing thresholds and 3.5 V (pacemaker default value) pacing were recorded, and RWA values were measured accordingly. The absolute values of I + aVL, II + III+ aVF, and V1 + V2 + V3 + V4 + V5 + V6 RWA were defined as X-, Y-, and Z-axis ΣRWA.

Results: A total of 195 consecutive patients (50 CLBBB and 145 narrow QRS) were enrolled (69.7 ± 10.3 years, 52.3% male). Compared with the baseline, LBBP significantly increased X- and Y-axis ΣRWA independent of pacing voltage in CLBBB (ΔX/Y-axis 0.49 ± 0.78 mV, p < 0.0001/0.61 ± 1.24 mV, p = 0.001) and narrow QRS group (ΔX/Y-axis 0.88 ± 0.61 mV, p < 0.0001/0.91 ± 1.05 mV, p < 0.0001); LBBP significantly reduced Z-axis ΣRWA in CLBBB patients (ΔZ-axis -2.64 ± 3.67 mV, p < 0.0001) but not in narrow QRS group (ΔZ-axis -0.14 ± 1.87 mV, p = 0.36). LBBP significantly improved cardiac function at 1 week of follow-up.

Conclusions: LBBP significantly increased X/Y-axis ΣRWA independent of pacing voltage in CLBBB and narrow QRS patients. LBBP significantly reduced Z-axis ΣRWA in CLBBB but not in narrow QRS patients. Whether these ΣRWA changes, through enhancing whole myocardial contractility, have a synergistic effect with LBBP synchronization to further improve cardiac function remains to be investigated.