ECHONOMY
Tools for Echocardiographic Calculations

Muhamed Saric, MD, PhD
New York University

## 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 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'.