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.