Flail Mitral Valve and Surgery

ABSTRACT & COMMENTARY

Synopsis: Moderate to severe mitral regurgitation due to flail leaflet is associated with excess morbidity and mortality.

Source: Ling LH, et al. N Engl J Med 1996;335: 1417-1423.

The timing of surgery for chronic mitral regurgitation remains problematic partly because of inadequate contemporary, longitudinal natural history studies. Consequently, the recently reported Mayo Clinic experience with mitral regurgitation due to flail leaflet is of interest. Ling et al studied 229 patients with flail leaflet diagnosed by two-dimensional echocardiography in the 1980s who had follow-up data obtained in 1994-95. In most cases flail leaflet was idiopathic (77%), but some were due to endocarditis (20%) and trauma (2%). In most patients, the posterior leaflet was involved, and about 70% had grade 3- 4/4 mitral regurgitation. Overall, mortality during medical treatment was 6% per year, which is higher than expected for an age-matched normal population. Multivariate predictors of mortality were age, NYHA class, and ejection fraction. Heart failure was common: 30% at five years; and 63% at 10 years. Independent predictors of heart failure were age, ejection fraction, and left atrial size. Atrial fibrillation occurred in 30% by 10 years but was not associated with increased mortality. By 10 years, 82% had undergone surgery, mostly for symptoms. The combined end point of surgery or death was 90% at 10 years. Post-surgical survival was 79% at five years and 66% at 10 years, which was not statistically different from an age-matched population. Surgery performed at any time favorably affected survival (hazard ratio, 0.29; 95% CI; 0.15-0.56, P < 0.001). The authors conclude that moderate to severe mitral regurgitation due to flail leaflet is associated with excess morbidity and mortality. Surgery is inevitable, and, when performed favorably, affects prognosis. Thus, surgery should be considered early after the diagnosis of flail mitral leaflet.

COMMENT BY MICHAEL H. CRAWFORD, MD

This is not a true natural history study since treatment was not withheld, but their observations are of value for managing patients with flail leaflets. Mitral valve surgery today is usually carried out for myxomatous disease rather than rheumatic disease and some have flail leaflets. In their series, most of the patients were men with ruptured chordae. How many were myxomatous is not stated. Also, the Mayo Clinic is a referral center. Thus, the patient population is somewhat unique, but well-characterized.

In their patients, mortality was 6% per year, which is similar to multivessel coronary artery disease. The excess mortality was seen mainly in patients who developed NYHA class III-IV heart failure symptoms even transiently (34%/yr) as compared to 4% in those with NYHA class I-II symptoms. Also, low left ventricular ejection fraction by echo was predictive of death; mortality doubled if the ejection fraction fell below 60% (5%/yr > 60%, 11%/yr < 60%). Although there are no prospective data showing that mitral surgery benefits patients with mitral regurgitation and low ejection fractions, they believe that their data showing surgery was an independent predictor of survival whenever it was done is strong support for operating on patients even with low ejection fractions. Some of their confidence is predicated on the fact that two-thirds of their patients had mitral valve repair and only one-fifth had concomitant coronary bypass surgery. Also, their surgical mortality was low at 4%. Thus, an aggressive approach may be justified in this selection population of mitral regurgitation patients due to flail leaflet.

Heart failure was the most common morbidity noted and reached 63% by 10 years. In addition to age, NYHA class, and ejection fraction, heart failure could also be predicted by left atrial size. The incidence of heart failure tripled when left atrial diameter on echo exceeded 30 mm/m2 (< 30, 5%; > 30, 15%). This is consistent with other echo data in heterogenous mitral regurgitation populations that show that left atrial size is an independent predictor of post-surgical outcome. Thus, the authors suggest that if left atrial size enlarges beyond 30 mm/m2 that surgery be considered in flail leaflet patients.

Since 141 of 143 patients had ruptured chordae and two had elongated chordae, in the 20% who had concomitant coronary bypass surgery, it must have been done for prophylactic reasons and was not likely the cause of their mitral regurgitation. Other studies have shown that mitral regurgitation due to coronary artery disease has a much worse surgical prognosis and surgery is probably contraindicated with low ejection fraction unless viable myocardia is demonstrated which could benefit from revascularization.

Overall, this study extends our knowledge concerning the timing of surgery for patients with chronic mitral regurgitation. When it is due to flail leaflet alone, early surgery is indicated with the expectation of mitral repair and a low operative mortality. In this select group, surgery should be considered in the asymptomatic patient if ejection fraction is less than 60% or left atrial size is greater than 30 mm/m2. This observational data is useful because surgery, heart failure, or death is inevitable in these patients, and early surgery before the latter two seems preferable.