Low Gradient Aortic Stenosis
Abstract & Commentary
Since patients with low gradient aortic stenosis are at higher risk for surgical replacement, more information concerning whom to select for surgery is desirable. Monin and colleagues from 6 centers in France studied 136 symptomatic patients with aortic valve area < 1.0 cm2, low cardiac index (< 3.0 l/min/m2) and a mean aortic pressure gradient < 40 mm Hg. All patients underwent dobutamine stress echocardiography (DSE) to a maximum dose of 20 mcg/kg/min. Decisions regarding surgery were made by the referring physician, who had knowledge of the DSE results. The majority of patients were men (96) and the mean age was 72 years. Almost all the patients presented with heart failure symptoms, and mean left ventricular ejection fraction (LVEF) was 0.30. About half of the patients had angiographic coronary artery disease (CAD), and two-thirds exhibited contractile reserve by DSE (stroke volume increase > 20%). Aortic valve replacement was done in 70% of the patients, and overall operative mortality was 14%. However, in the group with contractile reserve by DSE, operative mortality was 5% vs 32% in those without. Concomitant coronary artery bypass graft (CABG) surgery was performed in 25-30% of the patients and was associated with an increase in operative mortality to 11% in the contractile reserve patients and 62% in those without. By multivariate analysis, independent predictors of operative mortality were lack of contractile reserve (odds ratio [OR] = 11) and baseline mean aortic pressure gradient < 20 mm Hg (OR = 5). Predictors of long-term survival were aortic valve replacement (OR = 0.3) and contractile reserve (OR = 0.4). Improved functional class postoperatively was more common in those with contractile reserve (84 vs 45%; P = .002). Monin et al concluded that in low gradient aortic stenosis patients with demonstrable contractile reserve, surgery is generally beneficial. In those without contractile reserve, surgery is less beneficial due to a high operative mortality. Thus, DSE is of value for planning management in patients with low gradient aortic stenosis (Monin JL, et al. Circulation. 2003;108:319-324).
Comment by Michael H. Crawford, MD
In patients with a normal stroke volume, a mean aortic valve gradient of > 50 mm Hg corresponds to a valve area of < 1.0 cm2. When the calculated valve area is < 1.0 but the mean gradient is < 40 mm Hg, stroke volume must be low unless there is some error in the measurements. Such patients usually have reduced LV function and are at higher risk for valve replacement surgery. However, if such patients have LV contractile reserve that can be demonstrated by dobutamine stimulation, their prognosis with surgery is relatively good. On the other hand, those without demonstrable contractile reserve, especially if their resting mean gradient is < 20 mm Hg or if they have CAD, usually have a high mortality with surgery. Thus, the decision to pursue surgery in those with these negative predictors is a difficult decision because such patients do not do well with medical therapy either.
The other potential use for dobutamine stress echo is the identification of patients with relative aortic stenosis. These are patients with nonsevere aortic stenosis and marked cardiomyopathy in whom the stroke effort of the LV is insufficient to open the calcified aortic valve fully. In such patients, aortic valve area increases with dobutamine as the stroke volume rises. By contrast, those with true fixed aortic stenosis do not show a change in valve area with increased stoke volume. Relative stenosis patients were unusual in this large series. Only 5-7 of 136 patients met various criteria for this category, which is too small a number to say much about their long-term outlook.
There are several limitations of this trial. First, it was nonrandomized with regard to surgery. Second, the referring physicians decided on surgery, and they had access to the dobutamine data. Despite these potential biases, the same proportion of patients with and without contractile reserve were sent to surgery (70%). Third, even though it was a relatively large trial among valve disease studies, the number of patients was too small to answer many of the questions posed by the data, especially with regard to who should have surgery withheld. The most solid conclusion of the study is that DSE is useful in low gradient aortic stenosis patients for deciding who should have surgery.
Dr. Crawford, Professor of Medicine, Associate Chief of Cardiology for Clinical Programs, University of California, San Francisco, is Editor of Clinical Cardiology Alert.
Since patients with low gradient aortic stenosis are at higher risk for surgical replacement, more information concerning whom to select for surgery is desirable. Monin and colleagues from 6 centers in France studied 136 symptomatic patients with aortic valve area < 1.0 cm2, low cardiac index and a mean aortic pressure gradient < 40 mm Hg.
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