Calculate aortic valve area using the Gorlin formula or continuity equation. Classify aortic stenosis severity with AVAI indexing.
The aortic valve area (AVA) is a key parameter for quantifying the severity of aortic stenosis (AS), the most common valvular heart disease in developed countries. A normal aortic valve orifice measures 3.0–4.0 cm², but calcific degeneration, rheumatic disease, or congenital bicuspid anatomy can progressively narrow this opening, forcing the left ventricle to generate higher pressures to maintain forward flow.
Two primary methods are used clinically to determine AVA. The **Gorlin formula**, derived from hydraulic principles, uses data obtained during cardiac catheterization — cardiac output, heart rate, systolic ejection period, and the mean transvalvular gradient — to compute the effective orifice area. It remains a common invasive reference method. The **continuity equation** applies the conservation-of-mass principle to Doppler echocardiography data: the product of the left ventricular outflow tract (LVOT) cross-sectional area and velocity-time integral (VTI) equals the product of the aortic valve area and its VTI. This non-invasive method is commonly used in clinical practice.
Current ACC/AHA guidelines define severe AS as an AVA < 1.0 cm², a mean gradient > 40 mmHg, or a peak jet velocity ≥ 4.0 m/s. Indexing AVA to body surface area (AVAI) helps identify severe stenosis in patients with small body habitus, where an absolute AVA may be misleadingly "adequate." An AVAI < 0.6 cm²/m² is the threshold for severe disease. This calculator supports both the Gorlin formula and the continuity equation, providing AVA, AVAI, and a severity classification to assist in clinical education and decision-making.
Aortic valve area is most useful when it is read alongside gradient, velocity, symptoms, and valve morphology. This calculator keeps the math visible so the continuity equation and Gorlin formula can be compared without treating either one as a stand-alone treatment decision.
Gorlin Formula: AVA = (CO × 1000) / (HR × SEP × 44.3 × √ΔP), where CO = cardiac output (L/min), HR = heart rate (bpm), SEP = systolic ejection period (ms, converted internally to seconds), ΔP = mean gradient (mmHg). Continuity Equation: AVA = (LVOT Area × LVOT VTI) / AV VTI, where LVOT Area = π × (LVOT diameter / 2)². AVAI = AVA / BSA.
Result: 0.85 cm²
With a cardiac output of 5.0 L/min, heart rate 70 bpm, SEP 300 ms, and mean gradient 40 mmHg, the Gorlin formula yields an AVA of approximately 0.85 cm², indicating severe aortic stenosis.
Use the Gorlin formula when invasive hemodynamic data are available and the continuity equation when echo measurements are the available input. The two methods often agree in straightforward severe stenosis, but low-flow states, poor LVOT measurement, or discordant gradients can make the classification less direct.
The biggest source of error is measurement quality, especially LVOT diameter in the continuity equation and mean gradient interpretation in low-flow disease. When AVA is small but gradients are lower than expected, treat the result as a prompt to review the full echo or catheterization report rather than as a stand-alone diagnosis.
Indexing to body surface area helps in unusually small or large patients, but it does not replace the underlying valve assessment. Use AVAI as a sizing adjustment, not as a shortcut around clinical context.
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This page uses the Gorlin formula when invasive hemodynamic inputs are available and the continuity equation when echo measurements are available. AVA is then indexed to body surface area for a simple size adjustment. The output is a worksheet-style educational estimate, not a stand-alone diagnosis or treatment recommendation.
A normal aortic valve area in adults is 3.0–4.0 cm². Stenosis is classified as mild (1.5–2.0 cm²), moderate (1.0–1.5 cm²), or severe (< 1.0 cm²).
The continuity equation is the standard non-invasive method used during echocardiography. The Gorlin formula is used during cardiac catheterization when invasive hemodynamic data is available, or when echo results are discordant.
AVAI normalizes AVA for body size by dividing by body surface area. An AVAI < 0.6 cm²/m² indicates severe stenosis, which is especially important for patients with smaller body habitus.
The dimensionless index (or velocity ratio) is LVOT VTI divided by AV VTI. A value < 0.25 suggests severe aortic stenosis, independent of flow conditions.
No. This calculator is for educational purposes only. Aortic stenosis diagnosis requires comprehensive echocardiographic assessment and clinical evaluation by a cardiologist.
The Gorlin formula is flow-dependent, meaning it may underestimate AVA in low cardiac output states (low-flow, low-gradient AS). In these cases, dobutamine stress echocardiography may be needed.
SEP is measured from the beginning to the end of aortic valve flow during cardiac catheterization. It represents the time during each cardiac cycle when blood flows across the valve.