Aortic valve area calculation in aortic stenosis by CT and Doppler echocardiography

Abstract

Objectives: The aim of this study was to verify the hypothesis that multidetector computed tomography (MDCT) is superior to echocardiography for measuring the left ventricular outflow tract (LVOT) and calculating the aortic valve area (AVA) with regard to hemodynamic correlations and survival outcome prediction after a diagnosis of aortic stenosis (AS).

Background: MDCT demonstrated that the LVOT is noncircular, casting doubt on the AVA measurement by 2-dimensional (2D) echocardiography.

Methods: A total of 269 patients (76 ± 11 years of age, 61% men) with isolated calcific AS (mean gradient 44 ± 18 mm Hg; ejection fraction 58 ± 15%) underwent Doppler echocardiography and MDCT within the same episode of care. AVA was calculated by echocardiography (AVAEcho) and by MDCT (AVACT) using each technique measurement of LVOT area. In the subset of patients undergoing dynamic 4-dimensional MDCT (n = 135), AVA was calculated with the LVOT measured at 70% and 20% of the R-R interval and measured by planimetry (AVAPlani).

Results: Phasic measurements of the LVOT by MDCT yielded slight differences in eccentricity and size (all p < 0.001) but with excellent AVA correlation (r = 0.92, p < 0.0001) and minimal bias (0.05 cm(2)), whereas the AVAPlani showed poor correlations with all other methods (all r values <0.58). AVACT was larger than AVAEcho (difference 0.12 ± 0.16 cm(2); p < 0.0001) but did not improve outcome prediction. Correlation gradient-AVA was slightly better with AVAEcho than AVACT (r = -0.65 with AVAEcho vs. -0.61 with AVACT; p = 0.01), and discordant gradient-AVA was not reduced. For long-term survival, after multivariable adjustment, AVAEcho or AVACT were independently predictive (hazard ratio [HR]: 1.26, 95% confidence interval [CI]: 1.13 to 1.42; p < 0.0001 or HR: 1.18, 95% CI: 1.09 to 1.29 per 0.10 cm(2) decrease; p < 0.0001) with a similar prognostic value (p ≥ 0.80). Thresholds for excess mortality differed between methods: AVAEcho ≤1.0 cm(2) (HR: 4.67, 95% CI: 2.22 to 10.50; p < 0.0001) versus AVACT ≤1.2 cm(2) (HR: 3.16, 95% CI: 1.64 to 6.43; p = 0.005), with simple translation of spline-curve analysis.

Conclusions: Head-to-head comparison of MDCT and Doppler echocardiography refutes the hypothesis of MDCT superiority for AVA calculation. AVACT is larger than AVAEcho but does not improve the correlation with transvalvular gradient, the concordance gradient-AVA, or mortality prediction compared with AVAEcho. Larger cut-point values should be used for severe AS if AVACT (<1.2 cm(2)) is measured versus AVAEcho (<1.0 cm(2)).

Keywords: aortic valve stenosis; diagnostic method echocardiography; multidetector CT; survival.