Objective To assess the relationship between functional mitral regurgitation (MR) after a non-ST segment elevation acute coronary syndrome (NSTSEACS) and long-term prognosis, ventricular remodelling and further development of atrial fibrillation (AF), since functional MR is common after myocardial infarction.

Design and setting Prospective cohort study conducted in a tertiary referral centre.

Patients We prospectively studied 237 patients consecutively discharged in New York Heart Association class I–II (74% men; mean age 66.1 years) after a first NSTSEACS. All underwent an ECG the first week after admission and were echocardiographically and clinically followed-up (median 6.95 years).

Results MR was detected in 95 cases (40.1%) and became an independent risk factor for the development of heart failure (HF) and major adverse cardiovascular events (MACE) (per MR degree, HR_HF 1.71, 95% CI 1.138 to 2.588, p=0.01; HR_MACE 1.49, 95% CI 1.158 to 1.921, p=0.002). Left ventricular diastolic (grade I 12.7±40.7; grade II 26.8±12.4; grade III 46.3±50.9 mL, p=0.01) and systolic (grade I 10.4±37.3; grade II 10.12±12.7; grade III 36.8±46.0 mL, p=0.02) mean volumes were higher after follow-up in patients with MR, in proportion to the initial degree of MR. In the rhythm analysis (126 patients; previously excluding those with any history of AF) during follow-up, 11.4% of patients with degree I MR, 14.3% with degree II MR and 75% with degree III MR developed AF, while only 5.1% of those with degree 0 developed AF, p<0.001.

Conclusions MR is common after an NSTSEACS. The presence and greater degree of MR confers a worse long-term prognosis after a first NSTSEACS. This can in part be explained by increased negative ventricular remodelling and increased occurrence of AF.