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The issue of timing of surgical intervention for severe mitral regurgitation (MI) in patients who are asymptomatic remains controversial. This is the third in a series of reports from the Mayo clinic dealing with a large cohort of individuals with severe mitral regurgitation who were diagnosed with a flail mitral leaflet by 2-D echo between 1980 and 1989. The purpose of this observational study was to assess the long-term outcome in patients who were obvious surgical candidates for early mitral valve repair or replacement, and to compare their outcome to a group of subjects treated conservatively (no surgery). The primary focus was on long-term clinical outcomes, including total and cardiovascular mortality, as well as cardiovascular morbidity. The surgical group were operated upon within one month of diagnosis, whereas the conservative group were recommended for follow-up, typically because of no or minimal symptoms, or improvement of previous symptoms on medical therapy. A variety of clinical end points were evaluated on an intention to treat analysis. All patients had non-rheumatic, degenerative MR with flail or partially flail mitral leaflets. The overall cohort consisted of 221 patients (mean age 65; 70% male), of whom 63 underwent early surgery and 158 formed the conservative group. Eighty of the latter subsequently were operated on within 10 years; total follow-up was six to 15 years. Almost 90% of the conservative group were not operated on because of Class I-II status with or without medical therapy. Baseline characteristics between the two groups were relatively similar, although the early surgery group tended to be slightly younger, more symptomatic at entry, and had more atrial fibrillation. Left ventricular (LV) size and function, left atrial size, and etiology of the MR were comparable. The mean ejection fraction was 65%LV diastolic diameter was 35 mm/m2, and LV systolic diameter 20 mm/m2 in both groups. Grade III-IV MR was present by angiography or echocardiography in the large majority of patients. Approximately 20% of patients who went to early or late surgery had concomitant coronary bypass grafting. Two-thirds of both groups underwent mitral valve repair.
Results: The early surgery cohort demonstrated better overall survival as well as reduced cardiovascular death rate at both five and 10 years, with a 70% and 63% risk reduction, respectively. Overall survival for surgical patients was 89% and 79% at five and 10 years, respectively, and for the medical group, survival was 78% and 65%, respectively. As expected, cardiovascular mortality was comparably reduced in the early surgery group. By 10 years, 8% of the early surgery patients and 29% of the conservative group had suffered cardiac death. Multivariate analysis, adjusting for predictors of outcome, indicates that early surgery was independently associated with better overall survival. Congestive heart failure (CHF) was less in the early surgery patients, present in 18% and 25% at five and 10 years, respectively, vs. 26% and 59% in the medical patients, reflecting a 62% risk reduction. Fully 40% of the medical patients progressed to Class III-IV symptoms or developed CHF at follow-up; by 10 years, 58% had reached this end point. Atrial fibrillation was uncommon in the early surgery group, even at 10 years, whereas, by 10 years, 25% of the medical patients were in chronic atrial fibrillation. The incidence of endocarditis was low in both groups and only occurred in the conservative group. Thromboembolism and major bleeding events were comparable.
Ling and associates conclude that early surgery is an appropriate strategy for patients with severe MR related to flail leaflet, as reflected by the benign course of the early surgical cohort. Two-thirds of both groups underwent mitral valve repair rather than replacement, and Ling et al argue that this is a major factor supporting an early surgical decision.
The same group recently reported on the clinical outcome in these same patients analyzing early vs. late surgery results. In that report, the overall long-term clinical outcome of all subjects was analyzed (Ling LH, et al. N Engl J Med 1996;335:1417). Of the entire group, long-term survival at 10 years was somewhat below a life table analysis of comparable age patients but not dramatically so. Of the entire group (medical and surgical therapy), the 10-year death rate from cardiac causes was 33%, and the 10-year incidence of CHF was 63% with many patients moving to Class III-IV during follow-up. Independent predictors affecting long-term survival were the presence of symptoms, NYHA Class, the development of CHF, and surgical intervention. Of the 157 patients not immediately referred for surgery, the 10-year cumulative incidence of surgery, death, or both was 85%, leading to the conclusion that "death or the need for surgery is almost unavoidable within 10 years after diagnosis." Ejection fraction was an important predictor of outcome, with a mild decrease of LVEF (< 60%) predicting an increased risk of late mortality and CHF. In another report, the Mayo Clinic group makes a strong case for mitral valve repair as being the preferred surgical strategy (Enriquez-Sarano M, et al. Circulation 1995;91:1022-1028). This study included an even larger cohort of individuals who had echocardiography and severe organic MR. Left ventricular ejection fraction was slightly higher at baseline in the repair vs. replacement group and decreased to a slightly less degree post-op. They conclude that mitral valve repair in mitral valve prolapse or flail leaflet patients is related to a better outcome than mitral valve replacement.
The data in these three reports are compelling and supportive of a more aggressive approach to the minimally symptomatic or asymptomatic patient with severe MR, particularly if mitral valve repair appears to be feasible. However, it should be stressed that vasodilator therapy for MR was not employed in these patients, and long-term echocardiographic results are not reported. Those individuals who remained in Class I or II who continue to have preserved LV function appeared to do well and were crossed over to mitral valve surgery when LV function began to decline, symptoms occurred, or both. The dilemma of the truly asymptomatic individual with severe MR on a myxomatous or degenerative basis is not uncommon. Careful, continued clinical assessment, possibly with stress testing (not used by the Mayo Clinic) is critical. It is important to recognize that the estimated ejection fraction by echo or angiography in patients with several MR may be misleading regarding occult left ventricular contractile dysfunction. For a variety of reasons, it is known that an ejection fraction between 50% and 60% actually represents depressed function in such individuals and indicates a need for surgery. Conversely, if the ejection fraction is greater than 60% and LV cavity size remains only mildly enlarged, a watchful waiting policy appears safe in Class I-II patients. Nevertheless, the Mayo Clinic experience, with superb surgical results, is compelling and should mandate close follow-up of Class I-II patients with serial echocardiography and clinical assessment. These excellent long-term results indicate that mitral valve repair should be undertaken earlier than in the past, and no patient should be allowed to wait until the LV dilates and/or EF falls to the low to mid 50s. Also, an experienced surgeon who is skilled in mitral valve repairs is obligatory.