The Gorlin equation is used to calculate mitral or aortic valve area during invasive hemodynamic assessment via cardiac catheterization. While initially developed to measure mitral valve area in patients with rheumatic mitral valve stenosis, the Gorlin equation is not most commonly used to calculate aortic valve area in patients with aortic valve stenosis.

measured and used to calculate the valve area using the Gorlin equation below:

Aortic Valve Area (AVA) =          Cardiac Output          
                                               (SEP X HR * 44.3 * √G)

SEP = Systolic Ejection Period
HR = Heart Rate
G = mean pressure gradient across the aortic valve
√ = Square root

The cardiac output and pressure gradient are directly. Cardiac output is measured using the Fick method or thermodilution while the pressure gradient is found simply by using the catheter to measure the pressure in the aorta, then advancing it into the LV and taking another pressure reading (versus using a dual lumen catheter). The difference between these two pressures is the pressure gradient. The mean transaortic valve pressure gradient is used in the Gorlin equation to calculate the AVA, not the peak gradient.

It is important to note that the Gorlin formula was originally derived using patients with mitral stenosis and not aortic stenosis and thus may not relate perfectly to calculate the AVA. The Gorlin equation is also flow dependent, so if the patient has a significantly decreased ejection fraction, the AVA may be underestimated.