In individuals with normal aortic valves, the valve area is 3.0 to 4.0 cm2. As aortic stenosis develops, minimal valve gradient is present until the orifice area becomes less than half of normal. The pressure gradient across a stenotic valve is directly related to the valve orifice area and the transvalvular flow . As a result, in the presence of a depressed cardiac output, relatively low pressure gradients can be seen in some patients with severe aortic stenosis. (See "Low flow, low gradient severe aortic stenosis".) On the other hand, during exercise or other high flow states, systolic impulse-gradients can be measured in patients with minimally stenotic or even normal valves .
Complete assessment of the degree of aortic stenosis requires:
●Measurement of the transvalvular flow
●Determination of the transvalvular pressure gradient
●Calculation of the aortic valve area