Abstract & Commentary
Management of Severe Ischemic Mitral Regurgitation
By Michael H. Crawford, MD, Editor
Source: Acker MA, et al. Mitral-valve repair versus replacement for severe ischemic mitral regurgitation. N Engl J Med 2014;370:23-32.
Practice guidelines recommend mitral valve repair or replacement for severe ischemic mitral regurgitation (MR) that is causing symptoms refractory to best available medical therapy. However, few data exist to aid the selection of repair vs replacement. Thus, these investigators from the Cardiothoracic Surgical Trials Network conducted a randomized, multicenter trial of repair vs replacement in 22 centers involving 251 patients eligible for surgical treatment of their severe MR with or without coronary artery bypass grafting (CABG). Each surgeon decided on the best prosthetic valve or annuloplasty ring for the patient, but all the replacements had chordal sparing. The primary endpoint was the left ventricular end-systolic volume index (LVESVI) by echocardiography at 12 months. Secondary end-points included mortality, major adverse cardiac or cerebral events, serious adverse events, recurrent MR, rehospitalization, and quality of life.
Concomitant CABG was performed in 75%, and 11 of 126 patients in the repair group (9%) were converted to valve replacement. The ESVI at 12 months had decreased 7 mL/m2 in both groups. Mortality was 14% in the repair group and 18% in the replacement group (hazard ratio, 0.79; 95% confidence interval, 0.42-1.47; P = 0.45). Recurrence of moderate-to-severe MR at 12 months was 33% in the repair group and 2% in the replacement group (P < 0.001). Major and serious adverse events, functional status, and quality of life did not differ between the two groups. The authors concluded that there was no significant difference in LV function, mortality, or other clinical outcomes in patients who underwent repair vs replacement for severe symptomatic ischemia MR, but replacement resulted in a more durable result.
The management of severe symptomatic ischemic MR is a challenge. Most of these patients have low LVEFs, which are known to increase the risk of surgery, yet rarely does maximal medical therapy for LV dysfunction improve the MR and there is no specific medical therapy for MR. Although successful mitral valve surgery would eliminate MR, it is unclear whether the benefit would outweigh the risks of surgery. Consequently, the decision to operate for ischemic MR is usually in the context of CABG surgery. It has been said that severe MR with unrevascularized coronary artery disease is good news, since there is a good chance revascularization will improve or at least maintain LV function. In this study, 75% had concomitant CABG.
Based on the excellent results repairing mitral valves with degenerative disease, the majority of surgeons select mitral valve repair over replacement for ischemic MR. This practice is supported by observational studies that show superior results for repair. However, these observational studies require adjustments for baseline differences in repair vs replacement patients. One major difference is that repair patients have tended to be younger. Thus, a randomized trial was certainly in order and the results of this trial are contradictory to the observational studies. In addition to better matched groups with a randomized design, there are probably other differences that help explain the results. The 30-day mortality was lower in this trial (2% repair, 5% replacement) than in the Society of Thoracic Surgeon's database (5%, 9%). One reason for lower mortality in this trial may have been the exclusive use of a chordal sparing operation for replacement and the use of rigid or semi-rigid complete annuloplasty rings in all cases.
One fear in MR surgery cases is that once you close the low impedance leak to the left atrium, the ischemia weakened LV may be unable to handle the increased afterload and the EF will fall postoperatively. This was not the case in this study where LVEF remained almost the same postoperatively at around 40% in both groups. Although the 30-day mortality was higher with valve replacement, in the ensuing 11 months the death rate was the same in the two groups. Also, the most common causes of death were multiorgan failure (38%), heart failure (13%), and renal failure (10%), suggesting that the underlying ischemic cardiomyopathy played a big role in survival.
The primary endpoint of the study was LVESVI by echocardiography, which is an indirect marker of clinical outcomes. However, the authors point out that using mortality as an endpoint would have required 4000 patients and taken years to complete enrollment. A larger study that included a CABG alone arm would have been interesting. The investigators plan to follow the patients for at least another year, which may shed more light on the durability of repairs. As it is, at 1 year one-third of the repair group had moderate-to-severe MR. Given the poor durability of repair vs replacement and no other differences in outcomes, it would seem that surgeons should give more consideration to valve replacement for ischemic MR.