Ischemic mitral regurgitation (IMR) is defined as mitral valve (MV) insufficiency precipitated by myocardial infarction, with normal leaflet and chordal morphology. IMR usually occurs with right or circumflex coronary infarction involving the posterior ventricular wall, posterior papillary muscle, and adjacent mitral annulus.1 Common anatomic features include annular dilatation, displacement of papillary muscles, and varying degrees of leaflet restriction or tethering.1 There is a clear association between IMR and increased late mortality.2–7 Even after revascularization, IMR reduces late survival.2–7

Several studies have shown increased perioperative mortality for valve replacement in this situation, but the subject remains controversial.8–12

The objective of this study was to investigate the differences in immediate postoperative results (in-hospital complications and evolution) in patients with IMR undergoing coronary artery bypass grafting (CABG) with intraoperative correction of valve dysfunction by mitral valve replacement (MVR) compared with those undergoing CABG only.

The prevalence of moderate-to-severe IMR detected by transthoracic echocardiography and/or cardiac catheterization in myocardial infarction patients with coronary artery disease ranges from 3% to 12%.13,14 The prevalence of 8.1% observed in our study is within the range reported in the literature.

Mitral regurgitation causes atrial hemodynamic overload, which leads to tissue fibrosis; consequently, a non-homogenous distribution of diastolic depolarization potentials, refractory periods, and conduction properties occurs within the atrial muscle.15 All of these factors enhance the probability of reentry circuits forming around areas with longer refractory periods.15 MVR eliminates regurgitation, thereby reducing atrial hemodynamic overload and interrupting the cascade of events that culminates in the development of postoperative atrial fibrillation. In our study, the CABG+MVR group, despite longer exposure to CPB (known as a risk factor for developing postoperative AF16) showed a lower rate of AF than the CABG-only group (6.3% vs. 38.5%, p=0.021).

It seems logical to assume that the volume overload associated with mitral regurgitation will be particularly detrimental to patients with compromised LV function.17 There is also a loss of flow to the aorta, since part of the ejected volume is directed to the left atrium. MVR eliminates the volume overload and the loss of volume ejected toward the left atrium, displacing the entire cardiac output in the correct direction (to the aorta). This explains the lower rate of low cardiac output in the CABG+MVR group (despite longer exposure to CPB, known as a risk factor for development of postoperative low cardiac output16) compared to CABG only (6.3% vs. 42.3%; p=0.014).

Segmental wall motion abnormalities and LV distortion and remodeling after myocardial infarction displace the papillary muscles from the mitral annulus.18 This displacement puts excessive tension on the chordae, resulting in apical mitral leaflet tethering, restricting coaptation during systole.19–21 Leaflet tethering is compounded by LV contractile dysfunction, which decreases the closing force on the leaflets.21 Once IMR begins, end-diastolic LV volume and wall stress increase in tandem with preload.21 LV mass also increases progressively without a concomitant increase in end-diastolic wall thickness, resulting in generalized loss of myocardial contractile function.22 Increased wall stress causes further LV dysfunction,22 which in turn results in further papillary muscle displacement and leaflet tenting. If LV dilation occurs, it leads to annular enlargement and dysfunction, thereby increasing valvular incompetence.23 Chronic IMR therefore begets MR in a self-perpetuating manner. CABG surgery may interrupt the perpetuation and/or progression of this vicious cycle.

MVR is still a reasonable surgical option in many patients with IMR, mainly because of its reliability and reproducibility. It should be considered for patients with acute IMR, and for those with chronic IMR and multiple comorbidities, complex regurgitant jets (noncentral or more than one jet), or severe tethering of both MV leaflets.9,24,25

Some studies indicate greater perioperative mortality associated with this procedure, suggesting that preference should be given to less aggressive procedures such as CABG only or CABG associated with MVR.8,9 However, in our study, although the CABG+MVR group had a statistically significant higher prevalence of patients with worse functional class, there was no difference in operative mortality (6.3% vs. 7.7%; p=0.679) between groups. A possible explanation for this is that, unlike in other studies, MVR was the first choice for mitral valve surgery, and not a result of initial unsuccessful mitral valve repair (reoperation and/or prolonged CPB time as a function of failed valve repair might have increased operative mortality in this group). In addition, surgical intervention can prevent the LV overload and remodeling that results from mitral regurgitation, which may improve surgical outcomes.25

Goland et al.26 studied changes in LVEF in 83 patients with moderate IMR who underwent CABG associated with MVR (n=28) or CABG only (n=55). Patients who underwent CABG only showed significant improvement in LVEF in the early postoperative period (39±11 vs. 45±13; p=0.002), as did the CABG+MVR group (37±11 vs. 44±11; p=0.02). We also observed the same results of MVR, with the CABG+MVR group showing higher mean LVEF in the postoperative than in the preoperative period (54.13±4.51 vs. 45.25±4.54, p=0.041), as did the CABG-only group (52.92±4.25 vs. 48.62±4.19, p=0.049). So we observed improvement in postoperative LVEF in both groups. Furthermore, we found that the average gain in LVEF in the CABG+MVR group was higher than in the CABG-only group (8.88±2.39 vs. 4.31±1.23, p<0.001). As can be seen, in the case of LVEF, CABG+MVR provides better improvement than CABG only.

Although we did not analyze the approach to mitral valve repair, some considerations should be borne in mind. This is a technique intended to reduce or eliminate mitral regurgitation, while preserving the valve. Several investigators have suggested that repair is better than replacement for patients with IMR.11 Others, however, have documented similar survival after repair and after replacement.27 Late survival is poor for all approaches, with most patients dying within seven years of surgery.9 However, choice of surgical procedure has an important impact on survival. Among the most severely ill patients, the survival benefit of mitral valve surgery (by either valve repair or replacement) is diminished, which leads us to conclude that clinical status is an important determinant of survival.9 It seems that the “repair vs. replacement” debate remains undecided, although there is a strong tendency in the medical community in favor of repair.

Taking into account the severity of this population, patients who underwent CABG only or CABG+MVR surgery experienced no statistically different mortality rates, despite the presence of multiple comorbidities and impaired LVEF. MVR can be performed safely, concomitantly with CABG, in patients with moderate-to-severe IMR. In such patients, the combined procedure resulted in lower rates of postoperative atrial fibrillation and low cardiac output than CABG only. Both surgical approaches resulted in significant improvement in postoperative LVEF. However, there was greater improvement in the combined surgery group, which may result in greater benefit to this group. Despite being a more aggressive approach, the combined surgical procedure did not increase morbidity or mortality.

The authors have no conflicts of interest to declare.