The 2012 Randomized Ischemic Mitral Evaluation (RIME) trial randomized a total of 73 patients in the United Kingdom and Poland with moderate MR by echocardiography to isolated CABG vs CABG with concomitant MVR [27]. The study was concluded after 73 patients of a planned 100 after the primary endpoint – peak oxygen consumption – was reached after 1 year. Peak oxygen consumption has previously been recognized as a clinically-relevant measure of functional capacity. Patients undergoing CABG + MVR had a 22 % increase in peak oxygen consumption at 1-year compared to a 5 % increase in patients undergoing isolated CABG. Patients undergoing CABG + MVR had a median NYHA functional class of I, compared to median class of II in the isolated CABG group at the conclusion of the follow up period. The RIME study did not identify any difference in overall survival between the treatment arms, though again a small sample size and short duration of follow up limit the scope of long-term conclusions. Overall, the RIME study supported the addition of a mitral intervention in addition to revascularization with CABG.

Most recently, Smith et al. have reported the results of the largest trial to date designed to ascertain if the potential benefits of a combined CABG and mitral procedure outweigh the increased risks of the added intervention [28]. The Cardiothoracic Surgical Trials Network randomly assigned 301 patients across multiple centers with moderate ischemic mitral regurgitation as determined by transthoracic echocardiography to CABG alone or CABG plus mitral-valve repair (combined procedure). The primary end point was the left ventricular end-systolic volume index (LVESVI). At 1 year, significant reductions in the LVESVI were observed in both arms of the trial, but the addition of a mitral-valve repair to CABG did not result in a higher degree of left ventricular reverse remodeling. 69 % of patients in the CABG-alone group had no mitral regurgitation or mild regurgitation at 1 year, as compared with 89 % of patients in the combined procedure group. These findings suggest that revascularization alleviates reversible ischemia in both groups. Clinical outcomes at 1 year, including functional status, quality of life, mortality, need for mitral-valve reoperation, and major adverse cardiac or cerebrovascular events did not differ significantly between groups. The combined-procedure group did experience a higher rate of serious neurologic events and had a higher rate of supraventricular arrhythmias, likely related to the atriotomy mandated by the mitral valve procedure. Given that the addition of a mitral-valve repair to CABG did not result in a higher degree of left ventricular remodeling, but did lead to an increased number of untoward events, the trial did not show a clinically meaningful advantage of adding mitral repair to CABG.

The results of these three studies are in conflict. Taken together in recent meta-analysis, the addition of MVR to CABG in patients with moderate ischemic mitral regurgitation does reduce residual MR grade in short-term outcomes, but does so with a simultaneous increase in morbidity and does not offer improvement in mortality or other clinically-meaningful metrics. The opposing outcomes reached by these trials may reflect differences in the end points assessed, the methods of classifying mitral regurgitation, and baseline characteristics such as rates of prior myocardial infarction and duration of mitral regurgitation from initial diagnosis to trial enrollment. While there may well exist a patient population with moderate ischemic mitral regurgitation that will optimally benefit from CABG with concomitant mitral valve procedure in terms of survival, functional status, or symptoms, this patient population has not yet been conclusively identified in the literature. At present, a concomitant mitral valve procedure should not be routinely added to CABG for the treatment of moderate ischemic mitral regurgitation. Longer-term analyses of these trials will be of great value and will yield further insight into the long-term impact of revascularization in IMR. In particular, further assessment of the degree to which CABG can yield both long-term reversal of ventricular remodeling and improvement in clinical outcomes will be of extreme importance. Taken together, the best available evidence to date supports isolated CABG in the short term for the treatment of moderate ischemic mitral regurgitation. These data should be considered in the context of the individual patient who is evaluated for the treatment of ischemic mitral regurgitation in order to best identify an appropriately risk-stratified and individualized treatment plan.