Evaluation of an elliptical area technique for calculating mitral blood flow by Doppler echocardiography

To evaluate a method for measuring blood flow through the mitral valve 18 normal subjects and 19 patients with cardiac disease in whom mitral and aortic blood flows were identical were studied. Initially the mitral ring area was planimetered from the echocardiographic image, but the results of area calculation using the mathematical formula for the area of an ellipse were found to approximate to within 8% of the planimetered result in most cases. The formula was therefore used if the ring appeared elliptical on the cross sectional echo image, and other shapes were planimetered. Mitral velocity, aligned with flow in three planes, was recorded just distal to the ring. Mitral flow calculated using the elliptical technique correlated closely with flow measured in the ascending aorta by the Doppler technique and also with systemic flow measured by the Fick method at cardiac catheterisation in 10 patients. The mitral flow technique that assumed a circular orifice correlated almost as well with Doppler aortic flow and with Fick flow but overestimated flow by a mean of 1446 ml, whereas the elliptical method had a mean error of only 138 ml. Both methods correlated well with standards, but the elliptical method was easy to apply and gave a better correlation with comparison reference values.