Prevention of ischemic mitral regurgitation does not influence the outcome of remodeling after posterolateral myocardial infarction

Abstract

Objectives: This study was designed to test the hypothesis that ischemic mitral regurgitation (IMR) results from, but does not influence, the progression of left ventricular (LV) remodeling after posterolateral infarction.

Background: Surgical correction of chronic IMR is being increasingly recommended.

Methods: Three groups of sheep had coronary snares placed around the second and third obtuse marginal coronary arteries. Occlusion of these vessels in the control group resulted in progressive IMR over eight weeks. In a second group, Merseline mesh was fitted to cover the exposed LV before infarction. In a third group, a ring annuloplasty was placed before infarction to prevent IMR. Remodeling and degree of IMR were assessed with echocardiography at baseline and at 30 min and two, five, and eight weeks after infarction.

Results: Eight weeks after infarction, mean IMR grade was significantly higher in control animals than mesh and annuloplasty animals. At eight weeks, LV end-systolic volume and end-systolic muscle-to-cavity-area ratio (ESMCAR) were significantly better in mesh-treated sheep than in control sheep; also, at eight weeks, ESMCAR and akinetic segment length were significantly better in mesh-treated sheep than in annuloplasty sheep. Ejection fraction was significantly higher in the mesh than the annuloplasty group. There was no significant difference in any measure of remodeling between the annuloplasty and control groups.

Conclusions: Prophylactic ventricular restraint reduces infarct expansion, attenuates adverse remodeling, and reduces IMR severity. Prevention of IMR by prophylactic ring annuloplasty does not influence remodeling. Ischemic mitral regurgitation is a consequence, not a cause, of postinfarction remodeling; infarct expansion is the more important therapeutic target.