# Aortic Valve Area Calculator

Estimates aortic valve area (AVA) based on the continuity, Gorlin and Hakki equations.

Refer to the text below the tool for more information about these three indirect methods of determining AVA.

Aortic valve area calculation can be directly performed through planimetry during echocardiography or indirectly estimated through several equations based on clinical cardiological measurements.

AVA estimates are crucial in the diagnosis of aortic stenosis and its severity, along with the measurement of transvalvular flow and the determination of the magnitude and duration of the transvalvular pressure gradient.

### Continuity equation

AVA = LVOT diameter (in cm) x 0.78540 x LVOT VTI (in cm) / Aortic Valve VTI (in cm)

### Gorlin equation

AVA = Cardiac Output (in mL/min) / (Heart rate in beats/min x Systolic ejection period in seconds x 44.3 x Mean valvular gradient in mmHg)

### Hakki equation

AVA = Cardiac Output in L/min / Peak to peak gradient in mmHg

LVOT diameter
LVOT velocity time integral VTI
Aortic Valve VTI
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Cardiac output
Heart rate
Systolic ejection period
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Cardiac output
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Steps on how to print your input & results:

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## Determining aortic valve area

The aortic valve (one of the two semilunar valves of the heart) is situated between the left ventricle and the aorta. It is basically the last structure in the heart the blood goes through before entering the systemic circulation.

Aortic valve area calculation can be directly performed through planimetry during echocardiography or indirectly estimated through several equations based on clinical cardiological measurements.

Inadequate opening of the aortic valve, often resulting from calcification, leads to higher flow velocities through the valve and larger pressure gradients.

AVA estimates are crucial in the diagnosis of aortic stenosis and its severity, along with the measurement of transvalvular flow and the determination of the magnitude and duration of the transvalvular pressure gradient.

In adult individuals with normal aortic valves, the valve area is 3 to 4 cm2 and anything less than 1 cm2 is considered severe stenosis. The ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease define the following aortic stenosis severity degrees:

 Aortic Stenosis Severity AVA Mean pressure gradient Peak systolic flow velocity Mild > 1.5 cm2 < 25 mmHg < 3 m/s Moderate 1.0-1.5 cm2 25-40 mmHg 3-4 m/s Severe ≤ 1.0 cm2 > 40 mmHg > 4 m/s

## The continuity equation

The continuity equation for indirectly determining the aortic valve area is based on the assumption that the flow in one area must equal the flow in a second area (where no shunts exist). Which can be put in cardiac terms as the flow from the left ventricular outflow tract (LVOT) having to equal the flow at the level of the aortic valve.

`AVA = LVOT diameter2 x 0.78540 x LVOT VTI / Aortic Valve VTI`

Where all measurements are in centimetre.

The accuracy of this equation is limited by the accuracy of the three measurements involved, especially that of the LVOT diameter which is then squared in the equation.

## The Gorlin equation

Aortic valve area calculation by the Gorlin formula is an indirect method of determining AVA based on the flow through the valve during ventricular systole divided by the systolic pressure gradient across the valve times a constant (44.3). The below equation relies on the ratio of peak-to-peak instantaneous gradients.

`AVA = Cardiac Output / (Heart rate x Systolic ejection period x 44.3 x √Mean valvular gradient)`

Where:

• Aortic valve area is expressed in cm2;
• Cardiac Output is expressed in mL/min;
• Heart rate is expressed in beats/min;
• Systolic ejection period is expressed in seconds;
• Mean valvular gradient is expressed in mmHg.

Please note that at low cardiac output (less than 2,500 mL/min), the Gorlin equation tends to overestimate the degree of aortic stenosis.

## The Hakki equation

This is a simplification of the Gorlin equation that assumes that in most cases, the numerical value of the product of the heart rate, systolic ejection period and constant is approximately 1000.

In consequence, if Heart rate x Systolic ejection period x 44.3 is approx. 1000, then the equation becomes:

`AVA = Cardiac output (in L/min) / √Peak to Peak Gradient in mmHg`

## References

Chambers JB, Sprigings DC, Cochrane T, Allen J, Morris R, Black MM, Jackson G. Continuity equation and Gorlin formula compared with directly observed orifice area in native and prosthetic aortic valves. Br Heart J. 1992; 67(2): 193–199.

Hakki A, Iskandrian A, Bemis C, Kimbiris D, Mintz G, Segal B, Brice C. A simplified valve formula for the calculation of stenotic cardiac valve areas. Circulation. 1981; 63 (5): 1050–5.

Rifkin RD. Physiological Basis of Flow Dependence of Gorlin Formula Valve Area in Aortic Stenosis: Analysis Using an Hydraulic Model of Pulsatile Flow. J Heart Valve Dis. 2000; 9(6):740-51.

Gorlin R, Gorlin SG: Hydraulic formula for calculation of stenotic mitral valve, other cardiac valves, and central circulatory shunts. Am Heart J. 1961; 41:1-29.

Specialty: Cardiology

System: Cardiovascular

Abbreviation: AVA

Article By: Denise Nedea

Published On: June 7, 2020

Last Checked: June 7, 2020

Next Review: June 7, 2025