Left bundle branch pacing (LBBP) is a recent technique aiming at preservation of physiological ventricular electrical activation.

Our goal was to assess mechanical synchrony parameters in relation to electrocardiographic features during LBBP performed in routine practice.

From June 2020 to August 2021, all patients of our institution with permanent pacemaker implantation indication were eligible for LBBP. A “qR” pattern in V1 and a left ventricular activation time≤80ms in V5 defined a successful LBBP. Electrocardiogram and echocardiography were performed during spontaneous rhythm and LBBP: left ventricular mechanical asynchrony (LVMS) parameters using 2D Speckle tracking and interventricular mechanical delay (IVMD) were collected.

LBBP was attempted with success in 134/163 patients (82.2%). During LBBP, the mean QRS width was 104±12ms. In patients with left bundle branch block (n=47), LBBP provided a significant decrease of QRS width from 139±16ms to 105±12ms (P<0.001) with reduction of LVMS (53±21ms vs. 90±46ms, P=0.009) and IVMD (14±13ms vs. 49±18ms, P<0.001) (example in Fig. 1). In patients with right bundle branch block (n=38), LBBP led to a significant decrease of QRS width from 134±14ms to 106±13ms (P<0.001) with no effect on LVMS and a reduction of IVMD (17±14 vs. 50±16ms, P<0.001).

LBBP in routine practice preserved intra-ventricular mechanical synchrony in patients with narrow and RBBB QRS and improved asynchrony parameters in patients with LBBB.