In cases of mitral stenosis with suspected aortic stenosis, which calculation is used to determine the aortic valve area?

• A. Gorlin formula
• B. Continuity equation
• C. Bernoulli equation
• D. Doppler velocity index

Answer: (B)

The calculation relies on the continuity of flow: what moves through the left ventricular outflow tract must pass through the aortic valve. By measuring the LVOT cross-sectional area and the velocity-time integral (VTI) in the LVOT, you determine the forward stroke volume coming toward the valve. Then you compare that to the flow across the aortic valve by measuring the VTI of the aortic jet. The aortic valve area is given by the LVOT area multiplied by the LVOT VTI, divided by the aortic valve VTI.

In cases of mitral stenosis with suspected aortic stenosis, this approach is preferred because it calculates area from flow rather than relying on gradients that can be distorted by the mitral lesion and altered cardiac output. The Gorlin formula, used in catheter measurements, requires accurate cardiac output and pressure gradients and can be unreliable when there is another valvular disease affecting flow. The Bernoulli equation is for converting velocity to pressure difference, not for calculating valve area. The Doppler velocity index is a ratio used to assess severity but does not yield the actual valve area.