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
There is wide variability in the relationship between the severity of stenosis and symptom onset. In general, symptoms in patients with aortic stenosis occur when the valve area is <1.0 cm2 or the mean transvalvular gradient exceeds 50 mmHg (table 1). (See "Natural history of aortic stenosis in adults".)
This topic will review the methods of techniques for calculating the aortic valve area and valve resistance in patients with aortic stenosis. A discussion of the use of echocardiography in the evaluation of aortic stenosis is presented separately. (See "Echocardiographic evaluation of the aortic valve" and "Transesophageal echocardiography in the evaluation of aortic valve disease".)