Normal gradient across aortic valve can be measured by pulsed Doppler echocardiography as the gradients are low. In the presence of aortic stenosis, the gradients are high and needs continuous wave Doppler or high pulse repetition pulsed Doppler to measure trans aortic gradient as the velocities are above the Nyquist limit of conventional pulsed Doppler echo. Nyquist limit will be half the pulse repetition frequency. Hence it will be low for conventional pulsed Doppler with low pulse repetition frequency and high for high pulse repetition pulsed Doppler. Theoretically it is infinite for continuous wave Doppler.
In this image measurement of aortic peak gradient and mean gradient are illustrated. The early diastolic E and late diastolic A waves of mitral inflow are also demonstrated. Peak aortic gradient and mean aortic gradient are mildly elevated in this case. Such mild elevation of trans aortic gradients be noted in hyperdynamic states like severe aortic regurgitation. Similar gradients may also be seen across normally functioning prosthetic aortic valves. This is because any prosthetic valve in aortic location can intrinsically narrow the left ventricular outflow tract mildly, depending on the profile of the valve.