Effectiveness of fusion pacing in patients with left bundle branch block during left bundle branch area pacing

Left Bundle Branch Area Pacing (LBBAP) has emerged as a promising alternative for patients requiring cardiac resynchronization therapy (CRT), aiming to restore physiological ventricular activation. However, the role of optimizing atrioventricular delay (AV) during LBBAP remains underexplored. Fusion pacing seeks to enhance cardiac synchrony by combining paced activation of the left ventricle (LV) with intrinsic right bundle branch conduction. In patients treated with CRT, AV optimization to achieve fusion pacing using device-based algorithms has proven effective in narrowing the QRS duration (QRSd) and improving clinical outcomes. Similar benefits might be achievable with LBBAP; however, the impact of fusion pacing optimization in this context remains unexplored.

This study aims to evaluate the effects of AV optimization with fusion pacing on QRSd narrowing in patients with left bundle branch block (LBBB) undergoing LBBAP. To this aim, we utilized a device-based algorithm designed to measure intrinsic AV conduction and reduce it by a fixed offset.

We conducted a preliminary multicenter analysis on patients with LBBB and CRT indications treated with LBBAP, in whom AV optimization was performed to achieve fusion pacing. Within one month from the implant, patients underwent AV optimization using the Negative Hysteresis algorithm (Abbott), which measures intrinsic AV conduction and decreases it by a fixed offset ranging from 30 ms to 120 ms. The offset was adjusted iteratively, and for each value, the mean QRSd was recorded. The offset that resulted in optimal QRS duration narrowing was then definitively programmed.

A total of 10 patients (mean age 72 years, 55% male) with LBBB were included in the analysis. The mean intrinsic QRSd was 158±19 ms, while the mean QRSd during LBBAP with nominal AV settings (110/140 ms) was 137±30 ms. Fusion pacing was achieved in all patients using the device-based algorithm. The median offset that produced the maximum QRSd narrowing was 60 ms, and the mean QRS duration with the optimal offset was 131±23 ms. These results suggest that AV fusion pacing optimization leads to greater QRS narrowing compared to nominal AV delay and may significantly improve ventricular synchrony in patients with LBBAP.

Fusion pacing with optimized AV delay in LBBAP patients with LBBB shows potential for enhancing ventricular synchrony and improving hemodynamic stability by achieving significant QRSd narrowing. These preliminary findings support the further investigation of AV fusion pacing optimization as a therapeutic approach in LBBAP to enhance clinical outcomes. Future studies with larger cohorts are needed to confirm these benefits and evaluate the long-term impact on patient quality of life and survival.