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PapaHappyStar
The NEJM has an editorial on the topic as well in this months issue -- since it is an editorial its ok to quote it whole I guess --
Timing of Surgery in Asymptomatic Mitral Regurgitation
Catherine M. Otto, M.D., and Christopher T. Salerno, M.D.
The use of an evidence-based approach to the treatment of valvular heart disease has been hampered by the lack of rigorous data on predictors of the clinical outcome. The timing of surgery in patients with asymptomatic mitral regurgitation has been especially controversial for two reasons: the various causes of valve dysfunction and the lack of a precise measure of disease severity.1
Clinical outcomes and approaches to treatment depend on the cause of valve dysfunction. For example, in patients with secondary mitral regurgitation owing to dilated cardiomyopathy or ischemic disease, the prognosis depends mainly on the underlying disease and valve surgery remains controversial.2,3 In contrast, in patients with primary disease of the valve leaflets, such as mitral-valve prolapse, clinical outcomes are largely a consequence of backflow across the valve, so that restoration of valve competency is the logical treatment. In these patients, the main clinical question is when in the natural history of the disease the benefits of valve surgery outweigh the risks.
Until now, the timing of surgery for asymptomatic primary mitral-valve regurgitation has been based on both the appearance of symptoms and the hemodynamic consequences of the lesion, defined by the response of the left ventricle to chronic volume overload.4 In patients with symptomatic severe mitral regurgitation, surgical intervention is clearly needed. However, we cannot just wait for symptoms, because irreversible left ventricular systolic dysfunction may develop in the interim. Once left ventricular contractility is impaired, outcomes after surgical intervention are poor, with persistent symptoms of ventricular dysfunction and progressive heart failure. Thus, the goal in patients with severe mitral regurgitation is to identify the onset of left ventricular dysfunction so that surgical intervention can be performed promptly. Although there is no ideal measure of ventricular contractility, the empirical values that have been accepted as markers of early ventricular dysfunction in patients with severe mitral regurgitation are an end-systolic dimension of more than 40 or 45 mm and an ejection fraction of less than 60 percent.4 Other factors that suggest decompensation include pulmonary hypertension and new atrial fibrillation.
Now, we need to rethink our approach to the follow-up and treatment of patients with asymptomatic chronic mitral regurgitation. In this issue of the Journal, Enriquez-Sarano and colleagues5 present a landmark study of the natural history of mitral regurgitation in a large series of adults with asymptomatic isolated mitral regurgitation due to primary disease of the valve leaflets. The data strengthen the concept that asymptomatic mitral regurgitation is a serious disease, with a five-year rate of death from any cause of 22 percent and a 33 percent incidence of adverse cardiovascular events, including death from cardiac causes, heart failure, and new atrial fibrillation. Furthermore, this study focuses on regurgitant severity, instead of the ventricular response, as a predictor of the clinical outcome in patients with primary mitral regurgitation. As compared with patients with an effective regurgitant orifice of less than 20 mm2, patients with an effective regurgitant orifice area of at least 40 mm2 had more than five times the risk of death from cardiac causes and cardiac events. Those with an orifice area of 20 to 39 mm2 had intermediate outcomes.
Doppler detection of valve regurgitation has been a standard clinical tool for more than 20 years, but typically only a qualitative grade of severity (0 to 4+) is reported, and there is considerable interobserver variability in this grading scale. Color Doppler echocardiography still serves as a screening tool, with the narrowest segment of the proximal-flow stream, or vena contracta, used to identify patients who require further evaluation, but quantitation of valve regurgitation now includes calculation of the volume of backflow across the valve (regurgitant volume), the percent regurgitation as compared with the total stroke volume (regurgitant fraction), and the effective regurgitant orifice area, which is based on the same principles as the more familiar valve area for stenotic valves.6 Even though the regurgitant volume and fraction both depend on the driving pressure across the valve and the effective regurgitant orifice area may vary with valve dynamics, all these measures are far more accurate and reproducible than older approaches, such as the jet length or area on color Doppler echocardiography.
Although the predictive value of the effective regurgitant orifice appears to be high, caution is needed as we generalize this approach, for several reasons. First, the data of Enriquez-Sarano et al. apply only to patients with isolated primary mitral regurgitation; in patients with mixed-valve lesions, secondary mitral regurgitation, or left ventricular dysfunction, the situation is more complex. Second, quantitative evaluation of the severity of mitral regurgitation is time-consuming and technically demanding; accurate results depend on a meticulous approach by an experienced laboratory. Small errors in data recording or measurement lead to large calculation errors in the effective regurgitant orifice area. In addition, quantitation is more challenging when regurgitation is present only in late systole, as is often seen in patients with mitral-valve prolapse and in patients with atrial fibrillation. Finally, echocardiographic evaluation of the severity of regurgitation should integrate several anatomical and Doppler variables; reliance on a single measure for clinical decision making is hazardous. Ideally, quantitative variables should be reassessed at more than one time to ensure accurate data.
The decision to recommend surgery for an asymptomatic patient is always difficult; we need to be sure that earlier intervention results in better long-term outcomes than watchful waiting with prompt intervention based on conventional indications for surgery. Certainly, patients with an effective regurgitant orifice area of 40 mm2 or more should be monitored more closely. In addition, we may wish to offer selected patients earlier intervention after discussing the expected clinical outcomes, considering the effects of coexisting conditions, and weighing patients' preferences.7 A key factor in this decision is the likelihood that the valve can be repaired rather than replaced, a judgment that experienced echocardiographers can make.8 In a patient with a valve that can be repaired and a low expected perioperative risk of complications or death, earlier intervention might be reasonable. However, if valve replacement is likely to be needed or if the surgical risk is higher, the balance shifts toward watchful waiting. Ideally, the next step should be a prospective, randomized clinical study of early surgery as compared with surgery for conventional indications in patients with severe asymptomatic mitral regurgitation, defined on the basis of the effective regurgitant orifice area.
