Background and aim of the study: Ischemic mitral regurgitation (IMR) often persists, despite annular ring reduction. It has been hypothesized that persistent IMR following ring annuloplasty was related to a continued tethering of the mitral leaflets, as defined by the distance by which the papillary muscles (PMs) were displaced outside the mitral annular ring.
Methods: Seven sheep (four acute, three chronic) with persistent mitral regurgitation (MR) following ring annuloplasty for IMR were studied using three-dimensional (3D) echocardiography to examine the mitral valve geometry. The three stages examined were: Stage 1, baseline; Stage 2, post myocardial infarction (via ligation of the obtuse marginal branches); and Stage 3, post undersized ring annuloplasty. The 3D echocardiography measurements included mitral annular area, tethering distance from the ischemic PM to the anterior annulus, and the outside displacement of the PM relative to ring PM displacement.
Results: Persistent moderate MR remained in these seven sheep following undersized ring annuloplasty (MR vena contracta change (pre versus post ring): 7.0 versus 5.8 +/- 2.4 mm, p = NS), despite a reduction in the mitral annular area of 50 +/- 18% (10.3 +/- 6.3 versus 4.7 +/- 1.3 cm2). Ring annuloplasty shifted the posterior annulus towards the anterior annulus, such that the infarcted PM became displaced outside the mitral annulus. The projected displacement distance of the PM outside versus inside the annular ring was 8.4 +/- 2.4 mm outside mitral annulus post ring versus 3.6 +/- 2.5 mm within mitral annulus pre ring, p < 0001). The displacement distance from the infarcted PM to the mitral annulus restricted the ability of the posterior leaflet to move anteriorly, preventing effective coaptation. By multivariate analysis, this displacement distance was an important determinant of residual MR (p < 0.02).
Conclusion: Persistent MR following ring annuloplasty for IMR relates to persistently abnormal leaflet tethering, with restricted posterior leaflet motion due to PM displacement outside of the mitral annulus.