Impact of mitral regurgitation severity on thromboembolic risk in atrial fibrillation: a comprehensive systematic review and meta-analysis

Atrial fibrillation (AF) is associated with a heightened risk of thromboembolic events (TE). Whether severe mitral regurgitation (MR) has a protective effect against thrombus formation in AF remains unclear. We aimed to evaluate the impact of MR severity on thromboembolic risk in patients with AF. This systematic review with meta-analysis included data from eight studies, from 1998 to 2022. All studies reported the prevalence of TE according to MR severity, in patients with non-valvular AF, defined as the absence of prosthetic/repaired mitral valve or moderate or more severe mitral stenosis. TE was defined as stroke, transient ischemic attack, another arterial embolic event, or presence of thrombus in the left atrium. Eight studies with a total of 21,821 patients (54% male, mean age 70 ± 11 years) were identified. The overall prevalence of TE was 6.0%. No significant difference was observed in the prevalence of TE based on MR severity (no or mild MR: 5.9%, moderate or more severe MR: 6.8%, odds ratio: 1.11, 95% confidence interval: 0.77-1.73, p = 0.64). When specifically examining studies that exclusively reported either embolic or thrombotic events, there was no statistically significant difference in the incidence rates of events observed across the different categories of MR severity. Our analysis found no significant association between MR severity and the risk for TE, in patients with non-valvular AF. This suggests that MR may not be a determining factor for thromboembolic risk in this population.Clinical Trial registration (PROSPERO) CRD42024504403.