Aortic Valve Area Calculator (Continuity Equation)
Calculate aortic valve area (AVA) with the continuity equation from LVOT diameter and the LVOT and aortic VTIs — with indexed AVA, dimensionless index, peak gradient and the ACC/AHA aortic stenosis grade.
How it works
LVOT area = π × (LVOT diameter / 2)². Stroke volume = LVOT area × LVOT VTI. AVA = LVOT area × LVOT VTI / AV VTI. Dimensionless index = LVOT VTI / AV VTI. Peak gradient = 4 × Vmax² (simplified Bernoulli). Indexed AVA = AVA / BSA.
The continuity equation rests on conservation of flow: the stroke volume crossing the LV outflow tract equals the volume crossing the narrowed aortic valve. In the 2020 ACC/AHA valvular heart disease guideline, severe aortic stenosis is AVA 1.0 cm² or less (indexed 0.6 cm²/m² or less), peak velocity 4 m/s or more or mean gradient 40 mmHg or more; a dimensionless index of 0.25 or less also supports severe stenosis. LVOT diameter is squared, so a 1 mm measurement error changes AVA by about 10% — when the measures disagree, review the images.
Worked example
LVOT diameter 2.0 cm gives LVOT area π × 1.0² = 3.14 cm²; with LVOT VTI 20 cm the stroke volume is 63 mL. Divided by the aortic VTI of 80 cm, AVA = 0.79 cm² (severe), indexed 0.41 cm²/m² for BSA 1.9 m². The dimensionless index is 0.25 and a peak velocity of 4.0 m/s gives a peak gradient of 64 mmHg (severe).
Sources: Otto CM et al. — 2020 ACC/AHA Valvular Heart Disease Guideline · Baumgartner H et al. — EAE/ASE recommendations on echo assessment of valve stenosis
Frequently asked questions
What aortic valve area is severe aortic stenosis?
An AVA of 1.0 cm² or less (indexed 0.6 cm²/m² or less) is severe; 1.0–1.5 cm² is moderate; above 1.5 cm² is mild. Grading also uses peak velocity (≥ 4 m/s severe) and mean gradient (≥ 40 mmHg severe).
What is the dimensionless index?
The ratio of LVOT VTI (or velocity) to aortic VTI. It avoids the LVOT diameter error; a value of 0.25 or less suggests severe stenosis and 0.50 or more is usually normal for a native valve.
Why do AVA and gradient sometimes disagree?
A small area with a low gradient can mean low-flow, low-gradient stenosis (low EF or a small, thick ventricle) — or simply an underestimated LVOT diameter. Dobutamine stress echo or CT calcium scoring helps resolve it.
How is the mean gradient obtained?
It is traced from the continuous-wave Doppler envelope over systole by the echo machine. The peak gradient (4v²) shown here is an instantaneous value and is always higher than the mean.
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Clinical decision tool for education and for use by trained clinicians alongside clinical judgement — not a diagnosis and not a substitute for medical assessment. Formulas and cut-offs come from the cited sources; local protocols may differ.