Determination of the mean pressure gradient in aortic stenosis by Doppler echocardiography

Measurement of the mean pressure gradient across the stenotic aortic valve provides important information about the severity of aortic stenosis. However, determination of the mean pressure gradient by Doppler echocardiography has been difficult due to the squared relation between instantaneous velocities pressure gradients. In this study, the velocity curves in aortic stenosis were analysed mathematically to develop a new and simple method for calculating the mean pressure gradient (delta Pm) from Doppler velocity tracings. The new formula is: delta Pm = 8 V2m[Vp/(Vp + Vm)] where Vp is the peak systolic velocity and Vm the mean systolic velocity. Doppler echocardiography and cardiac catheterisation were performed in 41 patients with aortic stenosis to evaluate the accuracy of this mathematical method. There was a high correlation between the peak pressure gradients determined by Doppler technique using a modified Bernoulli equation and by catheterisation (r = 0.95, SEE = 8.58 mmHg), and the difference between the two measurements was not significant. The comparison between the mean pressure gradients determined by Doppler echocardiography using the new formula and by catheterisation yielded a high correlation (r = 0.95, SEE = 5.60 mmHg), and there was no significant difference between the two means. These results demonstrate the reliability of Doppler echocardiography for determining the mean pressure gradient in aortic stenosis using our mathematical method. Measurement of the mean pressure gradient will further enhance the usefulness of Doppler echocardiography in the non-invasive evaluation of patients with aortic stenosis.