Background: The novel method of left bundle branch pacing (LBBP) has been reported to achieve better electrical and mechanical synchrony in the left ventricle than conventional right ventricular pacing (RVP). However, its effects on right ventricle (RV) performance are still unknown. Methods: Consecutive patients undergoing dual-chamber pacemaker (PM) implantation for sick sinus syndrome (SSS) with normal cardiac function and a narrow QRS complex were recruited for the study. The pacing characteristics and echocardiogram parameters were measured to evaluate RV function, interventricular and RV synchrony, and were compared among ventricular pacing‐on and native‐conduction modes. Results: A total of 84 patients diagnosed with SSS and an indication for pacing therapy were enrolled. Forty-two patients (50%; mean age 65.50 ± 9.30 years; 35% male) underwent successful LBBP and 42 patients (50%; mean age 69.26 ± 10.08 years; 33% male) RVSP, respectively. Baseline characteristics were similar between the two groups. We found no significant differences in RV function [RV-FAC (Fractional Area Change)%, 47.13±5.69 vs. 48.60±5.83, p=.069; Endo-GLS (Global Longitudinal Strain)%, -28.88±4.94 vs. -29.82±5.35, p=.114; Myo-GLS%, -25.72±4.75 vs. -25.72±5.21, p=.559; Free Wall St%, 27.40±8.03 vs. -28.71±7.34, p=.304] between the native‐conduction or LBBP capture modes, while the RVSP capture mode was associated with a significant reduction in the above parameters compared with the native‐conduction mode (P < .0001). The interventricular synchrony in the LBBP group was also superior to the RVSP group significantly. Conclusion: LBBP is a pacing technique that seems to associate with a positive and protective impact on RV performance.

Abstract Background The paced morphology of right bundle branch block (RBBB) pattern is one of the parameters which can be used to confirm the left bundle branch capture during left bundle branch pacing (LBBP) implantation. However, changes of paced morphology after LBBP performed in patients with RBBB have not been well discussed. Objective To compare the paced morphology in patients with RBBB before and after LBBP and to discuss the possible mechanisms behind such changes. Methods Patients with RBBB who underwent LBBP implantation were selected. The QRS duration was measured before and after the implantation of LBBP for each patient and compared Student t test. Results We included 34 consecutive patients (median age 72.76 years, 73.53% male), of whom 3 had sick sinus syndrome (SSS) and 31 had high-grade atrioventricular conduction block (AVB). The average QRS duration was 144.87±5.22ms before LBBP implantation and 116.18±6.15ms after LBBP implantation, with a mean decrease in QRS duration of 28.70±3.30ms (95% CI: 27.55-29.85 ms, P < 0.01). Conclusion In patients with RBBB, the QRS duration after LBBP is narrower than that before LBBP. The specific mechanism is still unclear.