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

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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 (AVAproj), 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 AVAproj in a large series of patients and to propose a new clinically applicable simplified method to estimate AVAproj.

Methods

AVAproj 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: AVAproj = AVArest + slope × (250 − Qrest). 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 AVAproj 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 AVAproj demonstrated similar performance in discriminating true severe from pseudosevere AS (percentage of correct classification of AVAproj ≤ 1 cm2, 94% and 92%, respectively) and were superior to traditional dobutamine stress echocardiographic indices (percentage of correct classification, 60%-77%). Both conventional and simplified AVAproj 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 AVAproj ≤ 1.2 cm2 (hazard ratio, 1.65; P = .02) and simplified AVAproj ≤ 1.2 cm2 (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, AVAproj better predicts underlying AS severity and patient outcomes than traditional dobutamine stress echocardiographic indices. Simplified AVAproj is easier to calculate than conventional AVAproj, facilitating the use of AVAproj in clinical practice.

Section snippets

Methods

The protocol of the True or Pseudo Severe Aortic Stenosis (TOPAS) multicenter prospective observational study was described in detail in our previous publications.4, 5, 9 Briefly, between July 2002 and March 2008, we recruited 142 patients with low-flow, low-gradient AS, defined as AVA ≤ 1.2 cm2, indexed AVA ≤ 0.6 cm2/m2, a mean transvalvular gradient ≤ 40 mmHg, and an LV ejection fraction ≤ 40%. All patients underwent DSE using commercially available ultrasound systems, and functional capacity

Results

The mean age of the cohort was 73 ± 10 years, 108 (76%) were men. Systemic arterial hypertension was present in 60% of the patients, diabetes in 37%, coronary artery disease in 70%, multivessel coronary disease in 51%, and previous myocardial infarctions in 58%. Although 73 (51%) had no or minimal myocardial contractile reserve as defined by a percentage increase in stroke volume < 20%,3 the vast majority of the patients (92%) included in this series had significant increases in mean Q during

Discussion

We have previously reported that AVAproj can mitigate important interindividual variability in Q response during DSE and result in improved diagnostic accuracy compared with traditional dobutamine stress echocardiographic criteria for distinguishing TS from PS AS in patients with low-flow, low-gradient AS.9 However, the main limitations of the previous study were its limited sample size (n = 23), the absence of quantitative reference method to corroborate stenosis severity, and the absence of

Conclusions

Appropriate distinction between TS and PS AS is essential for therapeutic decision making in patients with LV dysfunction and low-flow, low-gradient AS. The results of this study demonstrate that AVAproj better predicts underlying AS severity and patient outcomes than traditional dobutamine stress echocardiographic indices in these patients. Importantly, simplified AVAproj is easier to calculate than conventional AVAproj, thus facilitating the use of AVAproj in clinical practice.

Acknowledgments

We thank Jocelyn Beauchemin and Isabelle Fortin for data collection and technical assistance.

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This work was supported by grant 57445 from the Canadian Institutes of Health Research (Ottawa, ON, Canada). Dr Pibarot holds the Canada Research Chair in Valvular Heart Diseases at the Canadian Institutes of Health Research. Dr Mathieu is a research scholar at Fonds de Recherches en Santé du Québec (Montreal, QC, Canada).

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