Left bundle branch pacing versus left ventricular septal pacing for cardiac resynchronisation therapy

Left bundle branch pacing (LBBP) has emerged as an alternative to conventional cardiac resynchronization therapy (CRT). While LBBP ideally achieves direct left bundle branch capture, left ventricular septal pacing (LVSP) is often observed in practice. The comparative clinical significance of LBBP versus LVSP concerning QRS reduction, left ventricular remodeling, and heart failure (HF) events requires further evaluation.

This single-center, retrospective study included all patients indicated for CRT in whom LBBP was attempted as first-line treatment between January 2021 and August 2024. We compared the effects of LBBP versus LVSP on QRS duration, left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV), NT-proBNP levels, and hospital admissions due to HF.

LBB capture was classified according to the European Heart Rhythm Association criteria: confirmed LBB capture (V6RWPT < 80 ms or V6-V1 interpeak interval > 44 ms) and likely LBB capture (V6RWPT < 100 ms or V6-V1 interpeak interval > 33 ms). Patients with confirmed or likely LBB capture were included in the LBBP group, while those not meeting these criteria were classified as LVSP.

An univariate analysis was performed to compare baseline subjects characteristics by group. Chi-squared test was performed to compare qualitative data and t-student test to compare quantitative data. Longitudinal measures over time were analysed using linear mixed models with repeated measures, with an unstructured covariance matrix.

The study included 75 patients with a mean age of 74 years. Baseline LBB block was present in 69 patients (92%), and 4 (5%) had right ventricular apex pacing.

Confirmed or likely LBB capture was achieved in 63% of patients. The LBBP group had a higher proportion of women (50% vs. 19%, p = 0.006) and lower rates of atrial fibrillation (30% vs. 59%, p = 0.02) and ischemic heart disease (11% vs. 37%, p = 0.01) compared to the LVSP group.

LBBP resulted in greater QRS narrowing (mean reduction: 42 ms vs. 26 ms, p < 0.001), greater improvement in LVEF (+16% vs. +9%, p < 0.001), and a trend toward greater reduction in LVEDV (-41 mL vs. -22 mL, p = 0.08) compared to LVSP. No significant difference in NT-proBNP reduction was observed. Detailed study results are provided in Tables 1 and 2.

During a mean follow-up of 7 months, five HF hospitalizations occurred, all in the LVSP group (p = 0,01).

In this retrospective study, LBBP resulted in significant improvements in QRS duration and LVEF compared to LVSP, which may be associated with a lower rate of HF hospitalizations. These findings suggest that achieving LBB capture should be prioritized over septal pacing when LBBP is selected as the first-line resynchronization therapy.