Continuity Equation AVA
Enter LVOT diameter, LVOT velocity time integral (VTI), and aortic valve VTI obtained from pulsed and continuous-wave Doppler. The calculator derives LVOT area and aortic valve area using the continuity equation.
Measure in mid-systole, inner-edge to inner-edge, from parasternal long axis.
How to Use This Calculator
Acquire accurate measurements
Measure LVOT diameter in mid-systole from the parasternal long axis view. Obtain LVOT VTI (pulsed Doppler) and aortic valve VTI (continuous-wave Doppler) from apical views.
Enter the Doppler values
Input diameter in centimeters and both VTIs in centimeters. Ensure measurements represent the same cardiac cycle and heart rate.
Interpret severity
Review the computed AVA and compare with guideline thresholds for aortic stenosis severity. Correlate with gradients, symptoms, and left ventricular function.
Formula
LVOT area = π × (LVOT diameter ÷ 2)2
Aortic valve area (AVA) = (LVOT area × LVOT VTI) ÷ Aortic valve VTI
Continuity equation assumes conservation of flow across LVOT and aortic valve.
Full Description
The continuity equation integrates LVOT geometry with pulsed and continuous-wave Doppler velocities to derive aortic valve area. Accurate measurements are essential: small errors in LVOT diameter markedly influence calculated AVA. Guideline-based assessment of aortic stenosis severity combines AVA (<1.0 cm² indicating severe) with mean gradients, peak velocities, and clinical findings.
In low-flow, low-gradient states, additional parameters such as stroke volume index, dobutamine stress echocardiography, and CT-derived valve calcium scoring help clarify true severity. Always integrate AVA with patient symptoms and shared decision-making for valve replacement.
Frequently Asked Questions
How sensitive is AVA to LVOT diameter errors?
Very sensitive. Because LVOT area includes radius squared, a 5% error in diameter becomes a ~10% error in area. Prioritize precise measurement perpendicular to LVOT walls.
Can I use LVOT velocity instead of VTI?
Use VTIs whenever possible for stroke distance accuracy. Instantaneous velocities may underestimate stroke distance and produce erroneous AVA values.
What about subvalvular obstruction or AI?
Dynamic LVOT obstruction can invalidate LVOT flow assumptions. Significant aortic regurgitation increases flow and may affect AVA; interpret within the full clinical context.
When should CT or catheterization be used?
In discordant cases (AVA low but gradients low), additional imaging (CT planimetry, calcium score) or invasive hemodynamics help resolve severity before valve intervention decisions.