Mechanical resynchronization in left bundle branch block achieved by conduction system pacing: A strain-based...

Left bundle branch area pacing (LBBAP) improves synchronous left ventricular (LV) contraction and therefore emerged as an alternative to biventricular pacing for cardiac resynchronization therapy. However, the extent of mechanical resynchronization with LBBAP remains incompletely characterized.

To assess resynchronization following LBBAP in patients with baseline left bundle branch block (LBBB) or right ventricular pacing induced dyssynchrony, across the full range of left ventricular ejection fraction (LVEF).

This multicenter study included patients undergoing LBBAP with LBBB or need for upgrade from right ventricular pacing. Mechanical dyssynchrony and resynchronization were evaluated using septal strain imaging at baseline, early post-implantation, and late post-implantation. Global longitudinal strain (GLS), and mid-septal strain curves were analyzed.

Left bundle branch pacing (LBBP) during follow-up was confirmed in 71% of the patients, LV septal pacing (LVSP) in 14%, and deep septal pacing (DSP) in 15%. Septal strain patterns improved immediately and progressively after implantation (P = .01), with GLS increasing from -12 ± 6% at baseline to -15 ± 6% at follow-up (P < .001). Resynchronization was not significantly different between LBBP and LVSP, but was inferior in DSP, with lower Δ mid-septal peak septal strain (P = .004) and ΔLVEF (P = .03) at 1 year. In regression analysis, both LBBB-stages and type of LBBAP-capture were associated with reverse remodeling following LBBAP.

LBBAP provides substantial mechanical resynchronization with immediate and progressive improvements in septal mechanics. Resynchronization was not significantly different between LBBP and LVSP, but was attenuated in DSP, where residual dyssynchrony was associated with lower LVEF 1-year after implantation.