Abstract & Commentary
Should Asymptomatic Patients with Severe Mitral Regurgitation be Referred for Valve Repair?
By Jeffrey Zimmet, MD, PhD
Associate Professor of Medicine, University of California, San Francisco, Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center
Dr. Zimmet reports no financial relationships relevant to this field of study.
Source: Kang DH, et al. Early surgery versus conventional treatment for asymptomatic severe mitral regurgitation: A propensity analysis. J Am Coll Cardiol 2014; Mar 14. doi: 10.1016/j.jacc.2014.02.577. [Epub ahead of print.]
In patients with severe degenerative mitral regurgitation (MR), surgery is clearly recommended in the presence of any symptoms. In asymptomatic patients, current American College of Cardiology Foundation/American Heart Association (ACC/AHA) guidelines establish a class I recommendation for surgery in the presence of high-risk markers including reduced left ventricular ejection fraction (LVEF), increased LV end-systolic dimension (LVESD), and pulmonary hypertension. As surgical techniques and outcomes have improved, however, there has been a growing tendency to consider surgery in truly asymptomatic low-risk patients without high-risk descriptors, especially when mitral repair as opposed to replacement is felt to be feasible. This presumes the superiority of mitral repair as the surgical procedure of choice, due to lower perioperative mortality, better conservation of left ventricular geometry from preservation of valvular and subvalvular structures, and avoidance of long-term anticoagulation. Evidence for using severe MR itself as an indication for surgery has been distinctly lacking, however. While ACC/AHA guidelines assign a IIa indication for mitral repair when the success rate is expected to exceed 90%, the European Society of Cardiology guidelines recommend close monitoring for these patients, with surgery to be recommended later with the appearance of symptoms or certain echocardiographic markers.
The performance of an appropriately sized randomized, controlled trial (RCT) in this setting has well-recognized difficulties. While it is not an RCT, the study by Kang et al adds significantly to the data in this arena. Over the course of the period between 1996-2009, 610 consecutive patients with asymptomatic severe MR and no high-risk features were collected and analyzed in a prospective fashion. A total of 235 of these patients underwent early surgery in a non-randomized manner. The remaining 375 patients had conventional treatment, consisting of observation and referral for surgery for dyspnea, decreased LVEF or increased LVESD, or elevated pulmonary pressures. Propensity score matching was performed for the entire cohort, yielding 207 matched pairs for follow up. The primary outcome was cardiac death, with a secondary outcome defined as a composite of events including all-cause mortality, operative mortality, repeat mitral surgery, and hospitalization for congestive heart failure.
In the propensity-matched groups, the early surgery group had a significantly lower cardiac mortality rate (1 ± 1% vs 6 ± 2% at 12 years, P = 0.010) as well as a composite event rate (4 ± 2% vs 19 ± 4% at 12 years, P = 0.001). A subgroup analysis was also performed according to age, showing that the benefit of early surgery was significant only in the group ≥ 50 years of age. The authors concluded that in patients aged ≥ 50 years with asymptomatic severe MR, early surgery is associated with reduced long-term cardiac mortality and major events compared with conservative management.
In this relatively large cohort of propensity-matched patients with asymptomatic severe MR, early surgery was associated with lower rates of cardiac events and cardiac mortality. These results clearly back a strategy of referral to surgery based on severe MR alone. However, several points merit further discussion. In the overall cohort, only 92 events were recorded despite the relatively long-term follow-up. The baseline clinical and echocardiographic characteristics of the initial groups were not similar — the early surgery group had significantly larger regurgitant volume, LV and LA dimensions, and Charlson comorbidity index — necessitating the propensity score matching. This process, however, left us with only 61 outcome events, further weakening the quantitative value of the relative risk calculations.
One finding of the study was that fewer patients in the conventional watchful waiting group underwent mitral valve repair (as opposed to replacement), compared with the early surgery group (82% vs 94%, P < 0.001). The authors propose this as one of the findings of the study — that is, that a watchful waiting approach may lessen chances for repair compared with early surgery. Notably, we are not supplied with any information about why repair was not selected as often in the "conventional" group. In this non-randomized study, features unfavorable for repair may very well have been responsible for assignment to the watchful waiting group in the first place, thus weakening the value of that comparison.
While far from perfect, this study certainly adds to the growing body of knowledge supporting early surgery for asymptomatic severe MR. Until a definitive RCT is performed, these are among our best available data.