Elimination of ischemic mitral regurgitation does not alter long-term left ventricular remodeling in the ovine model

Abstract

Background: The efficacy of annuloplasty for ischemic mitral regurgitation (IMR) has been difficult to establish. Using an established ovine model of IMR, we tested the ability of ring annuloplasty to durably relieve IMR and reverse or limit progression of left ventricular (LV) remodeling during a clinically relevant follow-up period.

Methods: A posterolateral infarction known to result in chronic IMR was initiated in 33 sheep. Echocardiography was used to assess LV end diastolic and systolic volumes and IMR (0 to 4 scale) before and 8 weeks after infarction. Eight weeks after infarction, 20 surviving animals with > or = 2+ IMR were randomized (1:1) to no treatment or undersized, semi-rigid, complete ring annuloplasty placement. LV remodeling and IMR were assessed at 4 and 6 months after infarction.

Results: All animals had similarly sized LV volumes at baseline (end systolic, 27.8 +/- 4.6 mL; end diastolic, 53.5 +/- 6.4 mL). The 20 randomized animals survived to complete the study. The degree of IMR before randomization was similar in treatment (2.6 +/- 0.4) and control (2.8 +/- 0.3) groups. At the 6-month follow-up, the degree of IMR was significantly less in the annuloplasty group (0.3 +/- 0.1 vs 3.4 +/- 0.6); however, LV volumes in the treatment group were not significantly different from the control group (end systolic, 82.1 +/- 15.6 vs 81.1 +/- 8.6 mL; end diastolic, 110.4 +/- 22.1 vs 111.1 +/- 16.5 mL).

Conclusions: In a clinically relevant ovine model of IMR, annuloplasty provides durable relief from IMR during an extended follow-up period but does not significantly influence LV remodeling.

Fig 1

Flow chart showing the experimental protocol. (IMR = ischemic mitral regurgitation; MI = myocardial infarction.)

Fig 2

Infarct characteristics. (A) Posterior view of an ovine heart as viewed through a right thoracotomy. All branches of the circumflex coronary artery that cross the lateral margin of the left ventricle (LV) and supply the posterobasal wall between the lateral cardiac vein and the middle cardiac vein are ligated (RV = right ventricle.) (B) View of the ovine left ventricle open through the intraventricular septum 24 weeks after the posterobasal myocardial infarction depicted in Panel A. The infarct involves most of the posterior left ventricular wall and the entire posterior papillary muscle. (C) Infarct size as determined by postmortem planimetry in control and annuloplasty groups. Error bars represent standard deviations.

Fig 3

Echocardiographic data for annuloplasty group (dashed line) and control group (solid line): (A) Serial left ventricular (LV) end systolic volume normalized to preinfarction value. Annuloplasty was placed 8 weeks after myocardial infarction (MI) in the annuloplasty group. The control group received no treatment. (B) Serial left ventricular end diastolic volume normalized to preinfarction value. (C) Serial ejection fraction (EF). (D) Degree of mitral regurgitation (MR) on standard 0 to 4 scale. The only statistically significant difference between groups was the degree of mitral regurgitation at 16 and 24 weeks after myocardial infarction. Error bars represent standard deviations.