Aortic valve area

Aortic Stenosis Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Lakshmi Gopalakrishnan, M.B.B.S. [2]

Overview

Normal aortic valve offers little or no resistance to the blood flow across the valve despite the high flow velocities. With progressive aortic stenosis, the aortic valve orifice offers progressively greater resistance to the blood flow through the valve with subsequent reduction in the pressure gradient between the left ventricle and the aorta. Therefore, using both the pressure gradient across the valve and the surface area of the valve the severity of aortic stenosis can be estimated. The latter can be calculated using echocardiographic flow velocities while the trans-valvular pressure gradient can be calculated using the following equation:

Pressure Gradient = 4 x (velocity of blood through the valve)² mmHg

However, the absence of a large gradient across the aortic valve does not exclude the presence of critical aortic stenosis as evidenced by the presence of low gradient, low ejection and subsequent low flow aortic stenosis that is associated with poor clinical outcomes. Therefore, it is for this reason that the best measure of the severity of aortic stenosis is the aortic valve area and not the aortic valve gradient.

Cardiac Catheterization

Simultaneous measurement of left ventricular output (measures the flow through the aortic valve) and the pressure gradient across the aortic valve provides the essential variables that is required to calculate the aortic valve area and resistance.

Aortic Valve Area:

Aortic valve area can be calculated by the following two equations:

Aortic Valve Resistance:

• Cannon JD Jr et al, described the benefit of calculating aortic valve resistance in conjunction with the Gorlin formula to differentiate patients with true severe aortic stenosis from those with mild aortic stenosis.

• Aortic valve resistance can be calculated using the equation:

Aortic Valve Resistance (dyne seconds per cms⁵) = { (Mean Pressure Gradient between the left ventricle and aorta (mmHg) x Heart Rate (beats/min) x Systolic ejection period (secs/beat) ) ÷ Cardiac output } x 1.33

References

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