Non-invasive estimation of the mean pressure difference in aortic stenosis by Doppler ultrasound.

The mean pressure difference across the valve in aortic stenosis is an indicator of the severity of the obstruction to flow. Non-invasive determination of the mean pressure gradient by Doppler ultrasonography is, however, complicated by the squared relation between instantaneous velocities and pressure differences. The validity of a new simple formula for calculation of the mean pressure difference from the peak pressure difference was evaluated in 26 patients with aortic stenosis. The formula is: delta pmean = 0.64 delta ppeak, where delta pmean is the mean pressure gradient and delta ppeak the peak pressure gradient. There was a close correlation between the mean pressure differences determined by application of the formula to the peak pressure differences measured at catheterisation and the mean pressure differences obtained by planimetry (r = 0.97, SEE = 4.7 mm Hg). The correlation between mean pressure differences determined by continuous wave Doppler ultrasound and the formula and those measured by planimetry was also close (r = 0.91, SEE = 7.6 mm Hg) and only three patients showed a difference between the two methods of greater than 10 mm Hg. The new formula is a simple and reliable means of estimating the mean pressure difference from Doppler recordings and it facilitates the comparison of Doppler and catheterisation data.