Calculate aortic valve area using the Gorlin formula or continuity equation. Classify aortic stenosis severity with AVAI indexing.
The aortic valve area (AVA) is the single most important 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 the invasive gold standard. 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 now the most widely used approach 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.
Accurate quantification of aortic valve area is critical for timing surgical or transcatheter aortic valve replacement (TAVR). Both the Gorlin formula and continuity equation provide complementary data for clinical decision-making, and understanding their calculations helps clinicians interpret results in context. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation.
Gorlin Formula: AVA = (CO × 1000) / (HR × SEP × 44.3 × √ΔP), where CO = cardiac output (L/min), HR = heart rate (bpm), SEP = systolic ejection period (s), 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.
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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.