Aklog and associates34 addressed the question of whether CABG alone could correct moderate ischemic MR. In their study, 40% of the patients who underwent postoperative transthoracic echocardiography showed no improvement with CABG alone and were left with moderate or severe (3 to 4+) residual MR. Approximately 50% of patients had some improvement and were left with mild (2+) residual MR. Only a few patients (fewer than 10%) had significant improvement, with no more than trace (0 to 1+) residual MR. These results suggest that CABG alone has an inconsistent and relatively weak effect on moderate ischemic MR.
Only a few studies have addressed this issue directly, with contradictory conclusions.35 Three reports have suggested that CABG alone can correct ischemic MR. Balu and colleagues,36 in a report from 1982, presented preoperative and postoperative ventriculography data on a heterogeneous group of 12 patients with ischemic MR and suggested that CABG alone improves MR and functional status. However, this study was limited by the heterogeneity and small number of patients enrolled. In a more recent report, Christenson and associates37 reviewed data from 56 patients with severe LV dysfunction (ejection fraction less than 25%) and various degrees of MR on preoperative echocardiography who underwent CABG alone. On postoperative echocardiography, 93% of the patients had no more than trace (0 to 1+) MR, and the remaining patients had mild (2+) MR. The investigators concluded that “moderate co-existing MR seems to normalize after myocardial revascularization and should not be surgically corrected therefore at the primary operation.” However, this study also had several limitations that, in our opinion, make it difficult to interpret and do not justify this broad recommendation. Most importantly, only seven patients (13%) in the study had moderate (3+) preoperative MR, and 40% had trace (1+) MR. In addition, nearly 10% of these patients underwent concomitant LV aneurysm repair, which can improve MR by decreasing ventricular dimensions. This fact may explain the unusually large increase in mean ejection fraction (18% to 44%) as compared with most reports on CABG in severe LV dysfunction. Kang et al38 assigned 107 patients with moderate to severe ischemic MR to CABG with concomitant MV repair (n = 50) or CABG alone (n = 57). The operative mortality in the combined CABG and MVR group was 12%, compared to 2% in the CABG-alone group. On follow-up, the 5-year survival rate was similar in both groups and approximated 88%. However, among the patients with severe MR, ischemic MR was improved in all patients of the repair group and in 67% of patients in the CABG group (P < .001), whereas improvement rates in patients with moderate MR were similar in the two groups. This study has several limitations: mainly, this was a nonrandomized study, implying an inherent selection bias. The series also included seven patients who underwent concomitant LV aneurysm repair for apical aneurysm, and the repair group had a higher percentage of patients with atrial fibrillation or severe MR than the CABG group. Moreover, on inspecting the survival curves, one sees that the repair-associated mortality occurs strictly in the early postoperative period, then the survival curves remain horizontal despite the higher risk profile in this group.
SIMRAM, an ongoing, large, prospective, multicenter, nonrandomized registry, is currently evaluating the effects of surgery on ischemic MR at rest and on its dynamic component at exercise.39 The SIMRAM registry is also designed to define the place of pre- and postoperative exercise testing in these settings along with the predictive factors affecting outcome. Prospective, randomized studies are also currently under way through the Cardiothoracic Surgical Trials Network (http://www.ctsurgerynet.org/) to assess the role of mitral valve repair in patients with ischemic or “functional” MR.