Surgical treatment:
There are multiple single center studies published to tackle the treatment of IMR. Virtually ball of these studies are not randomized and there are numerous confounding factors for each study. Until recently, there was few randomized controlled trials (RCT) focusing on the surgical management of the IMR. Over the last decade, we have been able to randomize patients to mitral valve surgery and coronary artery bypass grafting (CABG) and CABG alone, as well as CABG + mitral valve repair vs. CABG + mitral valve replacement. The results of the RCT studies are summarized in Table – 1 [41-46].
When the mitral regurgitation is severe, debate has focused on the choice between MVR or chordal-preserving mitral valve replacement as recently addressed by Goldstein et. al who randomized 251 patients with chronic IMR to undergo either mitral-valve repair or chordal sparing replacement with complete preservation of the subvalvular apparatus [46]. At two years follow up, authors conclude that there was no difference with respect to LV reverse remodeling or survival but the rate of recurrence of moderate or severe mitral regurgitation was more than 15 times higher with mitral-valve repair (58.8% vs. 3.8%) resulting in more heart failure—related adverse events and cardiovascular admissions [46]. When the regurgitation is only moderate, debate has centered on the role of associated MVR versus isolated coronary artery by-pass grafting (CABG) [47]. European guidelines on valvular heart disease have not clearly addressed the surgical treatment of moderate IMR and CABG. According to ESC guidelines, “there is continuing debate regarding the management of moderate ischemic MR in patients undergoing CABG and, in such cases, valve repair is preferable” [48]. Conversely, AHA/ACC guidelines consider surgical MVR at the time of CABG when the regurgitation is moderate as a class IIb-level of evidence C. This recommendation indicates that the procedure may be considered with benefit ≥ risk but additional studies are needed [48]. With this level of uncertainty and patients on the operating table, a randomized clinical trial on this issue is invaluable for making decisions in these challenging patients. Recently, Michler et al. have published the 2-year outcomes of this patient population. The investigators randomized 301 patients with moderate IMR and multivessel coronary artery disease to undergo either CABG alone or CABG and MVR. The primary end point was the degree of LV reverse remodeling, as measured by means of the LV end systolic volume index (LVESVI) on transthoracic echocardiography (TTE) 1 year after randomization. All patients were followed for 2 years with end points measured at 6, 12, and 24 months. Secondary end points included findings on TTE at other time points, rate of death, MACCE, defined as a composite of death, stroke, subsequent mitral-valve surgery, hospitalization for heart failure, or worsening New York Heart Association (NYHA) class, serious adverse events, degree of postoperative mitral regurgitation, quality of life, and rehospitalization [43]. At 2 years follow up, authors concluded that the addition of mitral-valve repair to CABG had no incremental effect on reverse LV remodeling. However, patients who underwent CABG alone had 3 times higher prevalence of moderate or severe mitral regurgitation than those who underwent the combined procedure (32.3% vs. 11.2%, P<0.001). Conversely, this difference did not translate into higher rates of death, MACCE, serious adverse events (including heart failure), or readmission during these 2 years of follow up.
Moreover, patients who underwent CABG plus mitral valve repair had higher self-reported exercise capacity. Patients randomized to MVR+CABG had longer operation time, longer cross-clamp and bypass times, which resulted in a longer postoperative length of stay during the index hospitalization, and significantly higher rates of serious neurologic events and supraventricular arrhythmias [44].
In summary, this trial concludes that patients who undergo CABG alone have less morbidity, same improvement on LV function and same rates of mortality (10.6% vs. 10%) and cardiovascular events than patients who undergo CABG plus MVR [44].
With these data, it would appear that the controversy is over and the problem is solved. What does IMR mean? In the current, AHA/ACC guidelines FMR occurs not only due to AMI but also reversible ischemia. If MR was caused by reversible ischemia rather than by nonviable scar formation, successful myocardial revascularization can lead to reduced LV size, increased mitral-valve closing forces, improved papillary-muscle synchrony, and enhanced contractility of subjacent myocardium. Therefore, treating these patients with CABG may result in a global improvement of the LV, hence improving mitral valve function.
So, one may conclude if mitral regurgitation and ventricular dysfunction may be correctable by revascularization alone, the performance of MVR would only add operative risk without any benefit.