The current study assessed the effect of mitral regurgitation (MR) on thrombotic risk in nonrheumatic atrial fibrillation (AF). AF carries a thrombotic risk related to left atrial blood stasis. The prevalence of atrial thrombosis, defined as the presence of left atrial appendage thrombus and/or left atrial spontaneous echo contrast grade >2, was determined in 686 consecutive nonrheumatic AF patients without (adequate) anticoagulation scheduled for transesophageal echocardiography before electrical cardioversion and was related to the severity of MR adjusted for the CHA2DS2-VASc score. A total of 103 (15%) patients had severe MR, 210 (31%) had moderate MR, and 373 (54%) had no-mild MR; the median CHA2DS2-VASc score was 3.0 (interquartile range 2.0 to 4.0). Atrial thrombosis was observed in 118 patients (17%). The prevalence of atrial thrombosis decreased with increasing MR severity: 19.9% versus 15.2% versus 11.6% for no-mild, moderate, and severe MR, respectively (p value for trend = 0.03). Patients with moderate and severe MR had a lower risk of atrial thrombosis than patients with no-mild MR, with adjusted odds ratios of 0.51 (95% confidence interval 0.31 to 0.84) and 0.24 (95% confidence interval 0.11 to 0.49), respectively. The protective effect of MR was present across all levels of the CHA2DS2-VASc risk score and the presence of moderate-severe MR in patients with an intermediate CHA2DS2-VASc score (2 to 3) lowered the atrial thrombotic risk to the level of patients with a low CHA2DS2-VASc score (0 to 1). In conclusion, our data show that the presence of MR attenuated the atrial thrombotic risk by more than 50% in patients with nonrheumatic AF.
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