Does Ischemic Mitral Regurgitation Regress After CABG?

Introduction:

Ischemic mitral regurgitation (IMR) is defined as mitral regurgitation secondary to ischemic heart disease, with no structural deformities of the mitral leaflets. Patients developing MR after acute MI have a worse prognosis than those who do not develop MR after MI, and late survival is related inversely to the degree of MR [1]. Patients undergoing coronary artery bypass grafting (CABG) often have varying degrees of MR. In cases of mild MR there is agreement that no intervention is required for the mitral valve. Similarly, if the degree of MR is severe, there is agreement that the mitral valve should be either repaired or replaced. In our experience with such patients in whom the left ventricle is severely impaired, mitral valve repair affords better survival than replacement [2]. In cases with moderate MR however, there is controversy in the literature. Some claim that revascularization is sufficient in moderate ischemic MR and performance of annuloplasty does not affect long term survival [3, 4]. However, there is ample evidence that CABG alone will not correct MR [5], and residual MR is associated with reduced survival [6], especially in patients with compromised LV function [7], and there is a higher incidence of late events [8]. Moreover, it is shown that performance of mitral annuloplasty does not increase the risk of surgery [9].

The purpose of this study is to determine whether repair of ischemic MR will improve survival and clinical status of patients undergoing coronary bypass surgery and have moderate MR.

Methods:

Patients

The study will be prospective randomized, and will include patients undergoing CABG and having MR of moderate degree. Patients with mild MR or severe MR will not be included. Patients with non-ischemic etiology for MR, or patients undergoing simultaneous aortic valve surgery will not be included. After signing an informed consent, each patient will be randomized to having intervention or no intervention on the mitral valve.

Patients who do not consent to randomization will not be included in the study. Whether to intervene on the mitral valve will be left to the discretion of the operating surgeon.

Echocardiographic evaluation

Trans-thoracic and/or trans-esophageal echocardiography will be performed to determine the degree of MR as well as left ventricular dimensions. The examinations will be performed at the following times: (1) before surgery; (2) in the operating room (under general anesthesia) before and after the surgical procedure; (3) before discharge; (4) at 3-6 months after surgery; at 12 months after surgery. Pre and post-operative trans-esophageal echocardiogram will be performed as clinically indicated.

The degree of MR will be determined according to TTE and TEE 2-D and doppler echocardiography validated criteria [10]. Moderate MR is defined by the following semi-quantitative criteria: regurgitant area 4-8 cm² or MRA/LAA 20-40% or vena-contracta 0.3-0.7 cm and no pulmonary vein flow reversal. Quantitative criteria: regurgitant volume 30-44 m”l and regurgitant fraction 30-39% and effective regurgitant orifice 20-29 mm².

The following echocardiographic parameters will be measured and recorded:

1.                                          Severity of MR (graded on a scale of 1-4) according to color jet area, proximal isovelocity surface area (pisa), vena contracta.

2.                                          LV dimensions including sphericity index (ration between LV major axis and minor axis); LV regional function.

3.                                          TI gradient (to assess pulmonary pressure).

Outcome

Outcome will be assessed at 1 week after surgery/ before discharge, at 1 month after surgery, at 6 and 12 months after surgery, and every 1-2 years thereafter.

Clinical parameters:

Operative mortality, symptoms, NYHA functional class, blood pressure, heart rate, need for diuretics.

Any adverse events: prolonged stay in ICU, prolonged hospitalization, infection, need for re-intervention.

Echocardiographic outcome:

Degree of MR, LV dimensions, LV function, LA dimensions, pulmonary pressure (TI gradient).

Endpoints

Long-term survival, NYHA functional class, repeat hospitalization, re-intervention (catheterization, repeat surgery), need for diuretics.

Degree of MR, LV dimensions, LV function, PA pressure (TI gradient).

Statistical analysis

Pre-operative variables, intra-operative and post-operative variables will be collected and analyzed. Factors associated with clinical or echocardiographic endpoints will be entered into univariate and multivariate analysis. Kaplan-Meier formulas will be used to assess survival and event-free survival of the two groups.

Summary

The best surgical treatment for ischemic MR of moderate degree is still unresolved. The low risk involved with concomitant repair and the potential benefit of a normally functioning mitral valve would favor performing a repair at the time of coronary bypass surgery. Indeed, our approach is to repair leaking mitral valves of moderate or greater degree. To our knowledge there are no prospective randomized studies regarding this issue. We propose to perform such a study in order to try to define the best surgical approach to patients with coronary disease having coronary bypass surgery, who have a moderately leaking mitral valve.