Acute Versus Chronic Ischemic Mitral Regurgitation

Background: Little is known on the mechanism of acute ischemic mitral regurgitation (IMR) caused by sudden-onset left ventricular dysfunction in acute myocardial infarction (MI). We sought to investigate the mitral valve (MV) complex geometry in acute IMR in comparison with chronic IMR by 2-dimensional and 3-dimensional transthoracic echocardiography. Methods and Results: Forty-four first-onset acute MI and 36 previous MI with ≥moderate IMR were examined by 2-dimensional/3-dimensional transthoracic echocardiography. MV morphology was quantitatively analyzed and compared between the 2 groups. Left ventricular end-diastolic volume and left ventricular end-systolic volume were significantly smaller in acute IMR than in chronic IMR (40.8 [33.1–48.3] versus 88.8 [66.5–108.8] mL/m 2 ; P <0.001, 17.8 [17.0–30.1] versus 49.5 [34.2–73.7] mL/m 2 ; P <0.001). MV tenting volume and annular area were significantly smaller in acute IMR compared with chronic IMR (0.98 [0.66–1.68] versus 1.88 [1.16–2.65] cm 3 /m 2 ; P =0.008, 5.17 [4.80–5.86] versus 5.81 [5.47–8.22] cm 2 /m 2 ; P =0.008). Leaflet surface area was significantly smaller in acute IMR than in chronic IMR (5.78 [5.16–6.32] versus 7.56 [6.89–11.32] cm 2 /m 2 ; P <0.001). The ratio of MV leaflet surface area and MV annular area was significantly smaller in acute IMR than in chronic IMR (1.08 [1.01–1.14] versus 1.28 [1.24–1.37]; P =0.001). Conclusions: Sudden-onset left ventricular dysfunction in acute MI may cause loss of coaptation of the MV even with a relatively mild degree of valve tethering. Compared with previously studied chronic IMR, a smaller leaflet area without leaflet adaptation and a larger hemodynamic burden at the acute onset of MI could result in clinically significant IMR despite relatively small leaflet tethering.