Mitral Leaflet Changes Following Myocardial Infarction

Abstract

Background— Ischemic mitral regurgitation (MR) is classically ascribed to functional restriction of normal leaflets, but recent studies have suggested post–myocardial infarction (MI) mitral valve (MV) leaflet fibrosis and thickening, challenging valve normality. Progression of leaflet thickness post-MI has not been studied. We hypothesized that excessive MV remodeling post-MI contributes to MR. Our objectives are to characterize MV changes after MI and relate them to MR. Methods and Results— Three groups of 40 patients with serial echocardiograms over a mean of 23.4 months were identified from an echocardiography database: patients first studied early (6±12 days) and late (12±7 years) after an inferior MI and normal controls. MV thickness was correlated with MR. We studied the mechanisms for MV changes in a sheep model (6 apical MI versus 6 controls) followed for 8 weeks, with MV cellular and histopathologic analyses. Early post-MI, leaflet thickness was found to be similar to controls (2.6±0.5 vs 2.5±0.4 mm; P =0.23) but significantly increased over time (2.5±0.4 to 2.9±0.4 mm; P <0.01). In this group, patients tolerating maximal doses of renin–angiotensin blocking agents had less thickening (25% of patients; P <0.01). The late-MI group had increased thickness (3.2±0.5 vs 2.5±0.4 mm; P <0.01) without progression. At follow-up, 48% of post-MI patients had more than mild MR. Increased thickness was independently associated with MR. Experimentally, 8 weeks post-MI, MVs were 2-fold thicker than controls, with increased collagen, profibrotic transforming growth factor-β, and endothelial-to-mesenchymal transformation, confirmed by flow cytometry. Conclusions— MV thickness increases post-MI and correlates with MR, suggesting an organic component to ischemic MR. MV fibrotic remodeling can indicate directions for future therapy.