MECHANISM OF FUNCTIONAL MITRAL REGURGITATION DURING ACUTE MYOCARDIAL-ISCHEMIA

The mechanism and temporal manifestation of functional mitral regurgit ation after acute myocardial ischemia were examined in eight dogs. Reg ional ischemia was produced by selective microembolization of the left circumflex coronary artery. Mitral regurgitation and regional left ve ntricular wall motion abnormalities were evaluated with use of Doppler color flow mapping and two-dimensional echocardiography, respectively . Measurements were made at baseline (before embolization) and were re peated at 30 min and 3 weeks after embolization. Mitral regurgitation developed in all dogs 30 min after embolization and completely subside d 3 weeks later. There was no evidence of mitral valve prolapse, mitra l anulus dilation or left ventricular segmental dyskinesia at any time during the study. Regional wall motion analysis showed only hypokines ia of the left ventricular segment overlying the papillary muscle at 3 0 min with subsequent normalization of the segment at 3 weeks. Mitral regurgitation was accompanied by an increase of the end-systolic dista nce between the mitral anulus plane and the point of coaptation of the mitral leaflets. This distance was 0.5 +/- 0.1 cm at baseline, increa sed to 0.9 +/- 0.1 cm 30 min after the embolization (p < 0.001) and re turned to near baseline (0.6 +/- 0.1 cm) 3 weeks after the embolizatio n. These data indicate that mitral valve prolapse, mitral anulus dilat ion and regional left ventricular dyskinesia are not necessary conditi ons for the development of functional mitral regurgitation after acute myocardial ischemia. Instead, hypokinesia of the ventricular segment overlying the papillary muscle and leading to retraction of the mitral leaflets toward the apex appears to be a sufficient condition for inc omplete leaflet coaptation.