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OBJECTIVE:
Being the aortic annulus elliptic, the continuity equation provides an underestimated value since it is obtained by the measurement of the distance between the nadir of the Non Coronary and the Right Coronary Valsalva sinuses (NC-RC) that usually corresponds to the ellipse short axis. Aim of the study was to validate a simple correction to the continuity equation in order to improve estimation accuracy.
METHODS:
We considered 13 patients, 10 male and 3 female with a mean age of 59.73±12.18 years. They have normal aortic root dimensions and a echocardiogram negative for valve diseases. All the patients underwent an
ECG-triggered thorax CT-scan that were then analysed and measured with the software Osirix. Of all these patients we tabulated all the aortic measurements. In the CT-scan images we measured the distance between the nadir of the NC and the RC Valsalva sinuses that is the diameter considered in the echo formula. We considered the echo diameter as the side of an equilateral triangle and through the Heron’s formula we calculated the area of the circumference circumscribed to this triangle. We compared the area obtained with the continuity equation and the one estimated with Heron’s formula to the one directly measured at the CT-scan by paired t-test.
RESULTS:
The aortic area measured at the CT-scan resulted 4.53±1.01, the area estimated with the continuity equation was 3.43±0.85 and the area calculated with our corrected equation was 4.57±1.13. The difference between the continuity equation estimation of the aortic valve area and the measured one turned out to be statistically significant (>0.01) while no statistically significant difference was found between the estimation with our corrected equation and the CT-scan measurements (p=0.93).
CONCLUSIONS:
The functional aortic area calculated with the continuity equation is
underestimated by 33%. Our correction is easy to apply and seems to perfectly fit the elliptical area of the LVOT leading to a more correct aortic valve stented prosthesis estimation .