Validation of conventional and simplified methods to calculate projected valve area at normal flow rate in patients with low flow, low gradient aortic stenosis: the multicenter TOPAS (True or Pseudo Severe Aortic Stenosis) study

Background: It has been previously demonstrated that a new index of aortic stenosis (AS) severity derived from dobutamine stress echocardiography (DSE), the projected aortic valve area (AVA) at a normal transvalvular flow rate (AVA(proj)), is superior to traditional Doppler echocardiographic indices to discriminate true severe from pseudosevere low-gradient AS. The objectives of this study were to prospectively validate the diagnostic and prognostic value of AVA(proj) in a large series of patients and to propose a new clinically applicable simplified method to estimate AVA(proj).

Methods: AVA(proj) was calculated in 142 patients with low-flow AS using 2 methods. In the conventional method, AVA was plotted against mean transvalvular flow (Q) at each stage of DSE, and AVA at a standardized flow rate of 250 ml/s was projected from the slope of the regression line fitting the plot of AVA versus Q: AVA(proj) = AVA(rest) + slope x (250 - Q(rest)). In the simplified method, using this equation, the slope of the regression line was estimated by dividing the DSE-induced change in AVA from baseline to the peak stage of DSE by the change in Q.

Results: There was a strong correlation between AVA(proj) calculated by the two methods (r = 0.95, P < .0001). Among the 142 patients, 52 underwent aortic valve replacement and had underlying AS severity assessed by the surgeon. Conventional and simplified AVA(proj) demonstrated similar performance in discriminating true severe from pseudosevere AS (percentage of correct classification of AVA(proj) < or = 1 cm(2), 94% and 92%, respectively) and were superior to traditional dobutamine stress echocardiographic indices (percentage of correct classification, 60%-77%). Both conventional and simplified AVA(proj) correlated well with valve weight (r = 0.52 and r = 0.58, respectively), whereas traditional dobutamine stress echocardiographic indices did not. In the 84 patients who were treated medically, conventional AVA(proj) < or = 1.2 cm(2) (hazard ratio, 1.65; P = .02) and simplified AVA(proj) < or = 1.2 cm(2) (hazard ratio, 2.70; P < .0001) were independent predictors of mortality. Traditional dobutamine stress echocardiographic indices were not predictive.

Conclusion: In patients with low-flow AS, AVA(proj) better predicts underlying AS severity and patient outcomes than traditional dobutamine stress echocardiographic indices. Simplified AVA(proj) is easier to calculate than conventional AVA(proj), facilitating the use of AVA(proj) in clinical practice.