User Rating 0.0 ★★★★★

Total Usage 0 times

Category Health & Nutrition

LVOT Diameter (cm) Range: 1.0 – 3.5 cm

LVOT VTI (cm) Range: 5 – 60 cm

AV VTI (cm) Range: 10 – 200 cm

BSA (m², optional) For indexed AVA. Range: 1.0 – 3.0 m²

Quick Presets:

Is this tool helpful?

Your feedback helps us improve.

★ ★ ★ ★ ★

About

Accurate determination of aortic valve area (AVA) is the cornerstone of aortic stenosis grading. Miscalculation leads directly to inappropriate surgical timing: operate too early and expose the patient to procedural risk without benefit; operate too late and face irreversible myocardial damage. The Continuity Equation derives AVA from the principle of conservation of mass, equating flow through the left ventricular outflow tract (LVOT) to flow across the stenotic valve. It requires precise measurement of LVOT diameter, LVOT velocity-time integral, and aortic valve velocity-time integral. A 1mm error in LVOT diameter propagates as a squared error in the final area, because the cross-section is computed as π × (d ÷ 2)². This tool implements both the Continuity Equation and the Gorlin formula, grades severity per ACC/AHA 2020 valve disease guidelines, and computes the Dimensionless Velocity Index for cross-validation.

Limitations: the Continuity Equation assumes a circular LVOT and laminar flow. The Gorlin formula loses accuracy at low flow states (cardiac output < 3.0 L/min) and in atrial fibrillation where beat-to-beat variability degrades mean gradient accuracy. This calculator approximates the systolic ejection period from heart rate when not directly measured. Always correlate with clinical assessment.

Formulas

The primary method uses the Continuity Equation, derived from conservation of mass across the aortic valve:

AVA = A_LVOT × VTI_LVOTVTI_AV

where the cross-sectional area of the LVOT is:

A_LVOT = π × d_LVOT2² = 0.785 × d_LVOT²

The Gorlin Equation uses hemodynamic catheterization data:

AVA = CO44.3 × SEP × HR × √ΔP

The Dimensionless Velocity Index bypasses LVOT area measurement:

DVI = VTI_LVOTVTI_AV

Where: AVA = Aortic valve area (cm²), d_LVOT = LVOT diameter (cm), VTI_LVOT = LVOT velocity-time integral (cm), VTI_AV = Aortic valve velocity-time integral (cm), CO = Cardiac output (mL/min), SEP = Systolic ejection period (s/beat), HR = Heart rate (bpm), ΔP = Mean transvalvular pressure gradient (mmHg), 44.3 = Gorlin empirical constant.

Reference Data

Parameter	Mild	Moderate	Severe	Critical
AVA (cm²)	> 1.5	1.0 - 1.5	0.6 - 1.0	< 0.6
Indexed AVA (cm²/m²)	> 0.85	0.60 - 0.85	< 0.6	-
Mean Gradient (mmHg)	< 20	20 - 40	> 40	> 60
Peak Velocity (m/s)	2.0 - 2.9	3.0 - 3.9	≥ 4.0	≥ 5.0
Dimensionless Index (DVI)	> 0.50	0.25 - 0.50	< 0.25	< 0.20
Stroke Volume Index (mL/m²)	Normal flow: > 35		Low flow: ≤ 35
Normal AVA (cm²)	3.0 - 4.0
Gorlin Constant	44.3
LVOT Diameter Range (cm)	1.8 - 2.5 (typical adults)
Normal CO (L/min)	4.0 - 8.0
SEP Estimation	SEP ≈ 60% of systolic time
ACC/AHA Guideline	2020 Valvular Heart Disease Guidelines
ESC Guideline	2021 Valvular Heart Disease Guidelines
Intervention Threshold	AVA ≤ 1.0 cm² with symptoms or LVEF < 50%
Low-Flow, Low-Gradient	AVA < 1.0, MG < 40, SVI ≤ 35
Projected AVA Cutoff	≤ 1.0 cm² at normal flow rate

Frequently Asked Questions

Because LVOT area is derived from π × (d/2)², diameter is squared. A measured diameter of 2.0 cm yields an area of 3.14 cm², while 2.1 cm yields 3.46 cm² - a 10% overestimation of AVA from just a 1 mm measurement difference. This is the single largest source of error in the Continuity Equation. Measure LVOT diameter in the parasternal long-axis view in mid-systole, inner edge to inner edge, averaged over 3 cardiac cycles.

The Gorlin formula loses accuracy in low-flow states (cardiac output < 3.0 L/min) because the empirical constant of 44.3 was derived from normal-flow conditions. In low-flow, low-gradient aortic stenosis, the calculated AVA may underestimate true valve area. Dobutamine stress echocardiography should be performed to differentiate true-severe from pseudo-severe stenosis. Additionally, irregular rhythms like atrial fibrillation degrade the accuracy of mean gradient and cardiac output measurements.

The DVI (LVOT VTI / AV VTI) eliminates LVOT diameter from the calculation, removing the largest error source. A DVI < 0.25 indicates severe aortic stenosis regardless of LVOT measurement. It is particularly useful when LVOT diameter measurement is technically difficult (calcified annulus, poor acoustic windows). However, DVI cannot provide absolute valve area and does not replace AVA for surgical decision-making per ACC/AHA guidelines.

Small patients (BSA < 1.6 m²) may have an AVA of 1.1 cm² that represents functionally severe stenosis relative to their body size. The indexed AVA (AVAi = AVA / BSA) with a cutoff of < 0.6 cm²/m² for severe stenosis corrects for this. The 2020 ACC/AHA guidelines recommend considering indexed AVA especially in patients with extremes of body size. BSA is calculated using the Du Bois formula: BSA = 0.007184 × height⁰·⁷²⁵ × weight⁰·⁴²⁵.

This calculator estimates SEP from heart rate using the relationship: systolic duration ≈ (60 / HR) × 0.33 + 0.035 seconds, then SEP is approximated as systolic time × 0.75. At a heart rate of 70 bpm, this gives approximately 0.30 s. Direct measurement from the aortic valve Doppler envelope (onset to cessation of flow) is more accurate. In tachycardia (HR > 100), the estimation becomes less reliable because systole shortens proportionally less than diastole.

This paradoxical entity is defined as AVA < 1.0 cm², mean gradient < 40 mmHg, and stroke volume index ≤ 35 mL/m². It occurs in two phenotypes: classical (reduced LVEF < 50%) and paradoxical (preserved LVEF but small LV cavity, concentric hypertrophy). The classical form requires dobutamine stress echo to confirm true-severe stenosis by demonstrating AVA remains < 1.0 cm² at normal flow (> 250 mL/s). CT calcium scoring (Agatston ≥ 2000 in men, ≥ 1200 in women) provides flow-independent confirmation.