Aortic Valve Area Calculator

The normal aortic valve area is 3–4 cm². Symptoms of aortic stenosis typically do not appear until the AVA falls below 1 cm² (severe stenosis). Mild stenosis is generally defined as AVA > 1.5 cm², and moderate as 1.0–1.5 cm².

The continuity equation states that blood flow through the LVOT must equal flow through the aortic valve. The formula is: AVA = (LVOT diameter² × 0.7854 × LVOT VTI) / AV VTI. It relies on the principle of conservation of mass and is the most widely used echocardiographic method.

The Gorlin equation estimates AVA using invasive hemodynamic data: AVA = Cardiac Output / (Heart Rate × Systolic Ejection Period × 44.3 × √Mean Gradient). It was developed from cardiac catheterization measurements and uses the hydraulic orifice formula, whereas the continuity equation relies on Doppler echocardiographic data.

The Hakki equation is a simplified version of the Gorlin formula: AVA = Cardiac Output (L/min) / √Peak-to-Peak Gradient (mmHg). It provides a quick bedside estimate and is most accurate at normal heart rates (around 70–80 bpm). It may overestimate AVA at faster heart rates.

The VTI ratio is calculated as LVOT VTI divided by AV VTI. A ratio below 0.25 generally indicates severe aortic stenosis. It is useful when the LVOT diameter measurement is uncertain, as it does not depend on that measurement.

Indexed AVA is the AVA divided by the patient's body surface area (BSA), expressed in cm²/m². It accounts for differences in body size — an AVA of 1.0 cm² may be severe in a small patient but moderate in a larger one. Severe AS is typically defined as indexed AVA < 0.6 cm²/m².

Severe aortic stenosis is generally defined by AVA < 1.0 cm², indexed AVA < 0.6 cm²/m², mean gradient > 40 mmHg (or > 50 mmHg by some criteria), peak aortic velocity > 4.0 m/s, and VTI ratio < 0.25. All parameters should be interpreted together in clinical context.

Each equation uses different inputs and assumptions. The continuity equation uses Doppler-derived velocities, the Gorlin equation uses catheterization hemodynamics, and the Hakki equation is a simplified approximation. Discrepancies can arise from measurement variability, heart rate differences, or low-flow states. Clinical correlation is always recommended.