Predictors of functional mitral regurgitation improvement in patients with left bundle branch block treated with left bundle branch area pacing

Background: Functional mitral regurgitation (FMR) and its severity are associated with adverse outcomes in heart failure patients. This study aims to analyze the predictors of FMR improvement after successful left bundle branch area pacing (LBBAP) in patients with LVEF < 50% and complete left bundle branch block (CLBBB). Methods: Consecutive patients with LVEF < 50% and CLBBB who underwent successful LBBAP from July 2018 to July 2023 were retrospectively identified. Significant MR was defined as regurgitation of moderate severity or greater. Patients with significant FMR were included in the analysis. FMR improvement (FMRI) was defined as a reduction of at least one grade in regurgitation severity compared to baseline at 3 months or longer follow-up. Results: Among the 81 identified patients, 42 patients with significant FMR preoperatively were included. After LBBAP, QRS duration significantly shortened from 170.6 +/- 18.8 ms to 114.5 +/- 20.2 ms (p < .001). Significant FMR improves in approximately 76.2%, and the patients were divided into an FMRI group (n = 32) and a non-FMRI group (n = 10). Univariate analysis showed that absence of persistent atrial fibrillation, typical CLBBB, and left atrium diameter at baseline were associated with improvement of FMR after LBBAP. Of these variables, only absence of persistent atrial fibrillation remains an independent predictor in the multivariate model (OR 12.436, p = .009). Conclusion: LBBAP is able to improve FMR in heart failure patients who had CLBBB with LVEF < 50%. Meanwhile, the absence of persistent atrial fibrillation is an independent predictor of FMR improvement.