Abstract & Commentary
With Comment by Michael H. Crawford, MD, Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco, Editor, Clinical Cardiology Alert.
Synopsis: Quantitating mitral regurgitation by echocardiography predicts clinical outcomes and those with an EROA of at least 40 mm2 should be considered for surgery.
Source: Enriquez-Sarano M, et al. Quantitative Determinants of the Outcome of Asymptomatic Mitral Regurgitation. N Engl J Med. 2005;352:875-883.
Improved surgical techniques for mitral valve repair have raised the issue of valve surgery in asymptomatic individuals. However, imprecision in the echocardiographic assessment of regurgitation severity has hampered the development of new guidelines. Recently, the American Society of Echocardiography (ASE) developed quantitative valve regurgitation thresholds of severity. Thus, Enriquez-Sarano and colleagues assessed whether this severity categorization would predict patient outcomes in 456 asymptomatic patients enrolled prospectively over 9 years with at least mild isolated organic holosystolic mitral regurgitation. Patients with structurally normal valves, multivalve disease, low ejection fraction, or other nonvalvular causes of regurgitation were excluded. The ASE recommended techniques were used to quantify the regurgitant volume/beat and the effective regurgitant orifice area (EROA). The patients were largely middle-aged men who had mitral valve prolapse. The 5-year rate of total mortality was 22%, cardiac death 14%, and major events (death, heart failure, new atrial fibrillation) 33%. Survival was independently predicted by age, diabetes, and EROA. For each 10mm2 increment in EROA, the hazard ratio was 1.18 (95%, CI; 1.06-1.3; P <.01). An EROA > 40 mm2 exceeded the expected mortality of an age- matched population based upon US census data (58% vs 78% survival, P = .03). Comparing those with an EROA < 20 to those with > 40 mm2, the latter had a higher risk of total mortality (HR, 2.9, 1.33-6.32, P < .01); cardiac death (5.2, 1.98-14.4, P < .01); and cardiac events (5.7, 3.07-10.56, P < .01). Cardiac surgery was performed in 232 patients largely for symptoms or marked left ventricular or atrial volume increases. Surgery was associated with improved survival (0.28, 0.14-0.55, P < .01) and reduced heart failure (0.37, 0.17-0.79, P < .01), but increased new atrial fibrillation (5.95, 3.38-10.46, P < .01). Enriquez-Sarano et al concluded that quantitating mitral regurgitation by echocardiography predicts clinical outcomes, and those with an EROA of at least 40 mm2 should be considered for surgery.
Comment
This large, longitudinal, observational study clearly shows that quantitative measures of mitral regurgitation severity predict outcomes during medical management, and do so better than semi-quantitative or qualitative indices. Patients with an EROA of 40 mm2 or more and a regurgitant volume > 60 mL/beat have severe mitral regurgitation and should be considered for surgery, regardless of symptoms and left ventricular or atrial size and perform ance. This doesn’t mean that symptoms or left heart chamber parameters are no longer important; in this study, symptomatic patients, or those with left ventricular ejection fraction < .50, were excluded, since previous studies have shown that they benefit from surgery. EROA was the strongest predictor of outcome; when 40 mm2, the 5-year death or surgery incidence was 84%. Those with an EROA between 20 and 39 had initially lower event rates that increase with time. They should be carefully followed.
Those with an EROA < 20 mm2 had a better survival than that expected from US census data (91% vs 86%). Thus, quantitation of mitral regurgitation severity by echocardiography allows for the identification of a high-risk group among asymptomatic patients with normal ejection fraction that should be considered for surgery.
An interesting point in this study is the comparison of EROA to the traditional qualitative (semi-quantitative) grading of MR into grades 1-4. Taking their study group, 39% had EROA < 20, 28% had 20-39, and 43% had > 40. The same patients with the traditional system were 15% 1+, 11% 2+, 20% 3+, and 54% 4+. Thus, under the traditional system, 74% could be considered for surgery (3-4+ patients) vs 43% by EROA > 40 mm2. This suggests that current practice may be overestimating the number of patients who may benefit from mitral valve surgery. This observation, plus the variability between readers in applying the current system, argues that considerable uncertainty exists in the recommendation for valve surgery in asymptomatic patients. The quantitative approach, coupled with this new outcome data, should improve the situation.