Aortic Valve Area (Continuity Equation using VMax)
Definition of Aortic Stenosis Severity
Aortic Valve Area (VMax)
Aortic valve area can be calculated by using the principle of conservation of mass — "What comes in must go out". Although VTI is a more accurate method, using maximum velocities is simpler and can generate a very close result. The simplified continuity equation is based on the concept that in native aortic valve stenosis the shape of the velocity curve in the outflow tract and aorta is similar so that the ratio of LVOT to aortic jet VTI is nearly identical to the ratio of the LVOT to aortic jet maximum velocity (V).
Aortic valve area indexed to body surface area should be considered for the large and small extremes of body surface area.
For patients with prosthetic aortic valves, patient-prosthesis mismatch is suspected when effective orifice area (EOA) indexed to body surface area <0.85 to 0.9 cm2/m2. Patient-prosthesis mismatch is considered severe when EOA index <0.65.
EOA Index (cm2/m2)
Subvalvular velocity (m/s)
Maximum velocity across the valve (m/s)
Left ventricular outflow tract diameter (cm)
Weight (kg or lb)
Height (cm or in)
Aortic Valve Area (cm2)
Aortic Valve Area indexed to BSA (cm2/m2)
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