Mechanical synchrony and myocardial work in left bundle branch area pacing: comparison of different sites of stimulation

Left bundle branch area pacing (LBBAP) offers several advantages, particularly through enhanced electromechanical synchrony of the left ventricle compared to traditional pacing methods. However, the mechanical impact of pacing at various LBBAP sites remains under-investigated.

To assess the medium- to long-term performance of mechanical synchrony in a cohort of patients undergoing LBBAP, comparing different stimulation types through myocardial work (MW) and other echocardiographic parameters.

Patients with successful LBBAP for bradycardia pacing and preserved left ventricular ejection fraction (LVEF) were consecutively enrolled. During follow-up, mechanical synchrony was evaluated using 2D echocardiographic variables, myocardial strain, and the advanced myocardial work (MW) measurement. Two echocardiograms were obtained with a minimum interval of 30 minutes: one during paced rhythm and, if feasible, another during spontaneous rhythm. Different LBBAP modalities were classified based on current transitional and ECG criteria.

The analysis included 149 patients: 114 with left bundle branch pacing (LBBP) and 35 with left ventricular septal pacing (LVSP). The mean follow-up was 18.2 ± 7.2 months. At baseline, no significant differences in LVEF or QRS duration were observed between groups. At follow-up, paced LVEF was similar in both groups (57.9±4.4 for LBBP vs. 56.9±3.9 for LVSP; p=0.198), as was non-paced LVEF (57.4±5.3 vs. 56.2±6.5, p=0.367). While strain and MW parameters showed no statistically significant differences during paced beats, there was a trend toward higher Global Work Efficiency (GWE) in the LBBP group (88.9±4.5 vs. 87.2±3.9, p=0.077). No significant differences in these parameters were noted during intrinsic beats (Table 1), except for intrinsic left ventricular end-systolic volume, which was higher in the LVSP group (38.0±12.5 vs. 32.7±10.3, p=0.044). Differences between paced and intrinsic beats in LVEF, Global Longitudinal Strain, or GWE were not significant for either subgroup (Table 2). Additionally, no statistically significant associations were found between pacing site (left bundle trunk or any fascicle) and paced LVEF or any other mechanical synchrony parameter (supplementary table).

In real-world settings, medium- to long-term differences in classic mechanical synchrony parameters, as well as in more precise metrics like myocardial strain and myocardial work, appear negligible between different LBBAP modalities.

LBBP vs. LVSP mechanical parameters