Left fascicular pacing is not inferior to left bundle branch pacing in preserving ventricular mechanical synchrony and cardiac function

Background Left bundle branch pacing (LBBP) has emerged as a more physiological alternative to right ventricular pacing.However, capturing the pre-divisional LBB is not easy to accomplish. This study investigates if left fascicular pacing(LFP), defined as the capture of one of the LBB fascicles, could achieve comparable left ventricular (LV) mechanical synchronicity and cardiac function compared to LBBP. Methods Thirty-one patients with pacing indication for bradycardia were retrospectively collected: LBBP was successfully performed in 13 patients and 18 achieved LFP. All patients underwent echocardiography before and after implantation and at one-year follow-up. Left ventricular (LV) volumes, ejection fraction (EF) and global longitudinal strain (GLS) were measured. The lateral-septal (LW-SW) work difference was used as a measure of mechanical dyssynchrony. Septal flash, apical rocking and septal strain patterns were also assessed. Results Although LW-SW work difference were significantly higher in the LBBP groups than that in the LFP group at baseline(272±269 mmHg*% vs 25±279mmHg*%,p=0.02), a similar increase in LW-SW work difference was observed during follow-up(199±342 mmHg*% vs 371±384mmHg*%,p=0.21). In addition, both LFP and LBBP induced septal flash or apical rocking in some patients, and resulted in subtle changes in strain patterns, which were not significantly different between groups. At one year follow-up, LV ejection fraction (EF) remained almost unchanged in both LBBP and LFP patients(ΔLVEF: 1.1+3.1% vs -0.3±4.8%,p=0.35) , and global longitudinal strain (GLS) was slightly and equally decreased in LFP compared to LBBP (ΔLVGLS: -1.6±2.3% vs -1.2±2.7%,p=0.69). Conclusion LFP and LBBP did not differ in mechanical dyssynchrony or LV remodelling.