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ECHONOMY
Tools for Echocardiographic Calculations
Muhamed Saric, MD, PhD
New York University
 

AS - Continuity Eq

Purpose
To calculate aortic valve area using the continuity principle which states that the stroke volume that passes through the LVOT in systole is equal to the stroke volume passing through the aortic valve.

Technical Hints
Interrogate the Doppler flow through the aortic valve from any available echocardiographic window and use the highest Doppler values obtained.

Calculator
Body Surface Area    

Body Surface Area

 m2

 

 
LVOT Data    

LVOT Vmax
(by pulsed Doppler)

 m/sec

LVOT VTI
(by pulsed Doppler)

 cm

LVOT Diameter (d)

 cm
   

LVOT Area:

 cm2

LVOT Stroke Volume (SV)

 mL

LVOT Stroke Volume Index (SVI)

 mL/m2
     
Aortic Valve Data    

AV Vmax
(by continuous Doppler)

 m/sec

AV VTI
(by continuous Doppler)

 cm
   
AV Peak Gradient  mm Hg
**AV Mean Gradient  mm Hg
AV Area (AVA)  cm2
AV Area Index (AVAI)  cm2/m2
Dimensionless Index  
     

Formulas

LVOT Area = (1/2 * d)2 * pi

SV = LVOT Area * LVOT VTI
 

AV Peak Gradient - 4 * (AV Vmax)2


** AV Mean Gradient should be measured directly. Here a rough approximation is given as AV Mean Gradient = 2/3 * AV Peak Gradient

 

AVA = LVOT Area * (LVOT VTI / AV VTI)
 

Dimensionless Index = LVOT Vmax / AV Vmax

Reference
Skjaerpe T, Hegrenaes L, Hatle L. Non-invasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two dimensional echocardiography. Circulation 1985;72:810-8.

Note: Interestingly, the authors called the method 'equation of continuity' rather than 'continuity equation'.