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ABSTRACT & COMMENTARY
By Michael H. Crawford, MD, Editor
SOURCE: Castleberry AW, et al. Surgical revascularization is associated with maximal survival in patients with ischemic mitral regurgitation: A 20-year experience. Circulation 2014;129:2547-2556.
The optimal treatment for ischemic mitral regurgitation (MR) is controversial and suffers from a lack of sufficient study data to build a consensus. Thus, these investigators from Duke University Medical Center interrogated their cardiovascular disease database to shed light on this issue by performing a retrospective cohort analysis over 18.5 years of patients with significant coronary artery disease (CAD) and moderate or severe MR by cardiac angiography or echocardiography. Treatment was at the discretion of the attending physician and the patients were kept in the initial treatment category assigned to them for this analysis, which ignored crossovers. The primary outcome was overall survival. After excluding patients who did not meet entry criteria or who had significant cardiac and non-cardiac comorbidities, 4989 patients were included in the study — of which 36% received medical therapy, 26% percutaneous coronary interventions (PCI), 33% coronary artery bypass surgery (CABG) alone, and 5% CABG plus mitral valve (MV) replacement or repair. The majority of patients had three-vessel CAD and moderate MR. Significant differences in the characteristics of the patients assigned to these four treatment categories were found, as would be expected. During the first half of the study, medical management predominated and later CABG alone was most common. After a median follow-up of over 5 years, the median adjusted survival was 5.6 years for medical management, 6.8 years for PCI, 9.7 years for CABG alone, and 8.1 years for CABG+MV repair or replacement. Adjusted hazard ratios showed that CABG alone had the lowest risk of death (0.56; 95% confidence interval [CI], 0.51-0.62; P < 0.0001), CABG+MV repair or replacement 0.69, and PCI 0.83. Interestingly, when analyzed based on the severity of MR, the data were not significantly changed. The authors concluded that in patients with moderate or more ischemic MR, CABG alone exhibited the lowest long-term risk of death, and CABG with or without MV surgery showed a lower mortality compared to PCI or medical therapy alone.
The AHA/ACC guidelines recommend medical therapy for ischemic MR (class I), not because of compelling data to support this opinion, but rather due to the perceived high mortality of CABG plus MV repair or replacement.1 Surgery is recommended if other cardiac surgery is necessary (IIa) and primary mitral surgery with or without CABG can be considered (IIb). The level of evidence for any surgical therapy is C. This paucity of data makes the Duke database study, which includes almost 5000 patients with moderate-to-severe ischemic MR, of interest. Basically, they found the opposite compared to the guidelines recommendation. CABG surgery alone had the best long-term survival and was superior to that of CABG+MV repair or replacement, PCI, or medical therapy after adjustments for differences in the characteristics of the patients in each therapy group. This confirms an old adage that the ischemic myocardium prefers blood to drugs. So if MR is due to ischemia, relieving ischemia should reduce the MR regardless of any MV procedure. PCI, although better than medical therapy, was not superior to CABG, probably because revascularization by PCI is less complete in ischemic MR patients who often have severe three-vessel disease.
These retrospective, observational database studies often are deficient in the kinds of data that would clarify mechanisms in specific patients. In this study, we lack details that may clarify the decision making with the different types of patients. For example, we have no detailed non-invasive data in this study. It could be that if MR was largely due to infarcted and scarred walls and was severe, MV replacement would be the best treatment. On the other hand, MR purely due to ischemia would be expected to benefit from CABG alone. Thus, patient selection may have influenced the results in ways that propensity scoring cannot account for. Also, there is no quality of life or cost data. These considerations could influence treatment choice.
Although for a long-term database study this is fairly contemporary data, it does not reflect the latest developments in this area. We know some patients had mitral valve repair, but did they have the Alfieri technique done? This is a stitching of the two MV leaflet tips together at the center and creating a double orifice valve. Remarkably this reduces MR without causing significant stenosis and doesn’t appreciably affect surgical mortality. This concept has now been developed as a percutaneously placed clip (Mitraclip®). In Europe, where the clip has been available for a few years, it is mainly used for ischemic MR, often in combination with PCI. What this area needs are some randomized trials that would include these new technologies. Fortunately several are under way. Until the results of these trials are in, it would appear that more consideration should be given to CABG in patients with ischemic MR.