Aortic Stenosis on EchoCG: Severity Criteria and Low-Flow Pitfalls
Basic Parameters for AS Assessment
The main echocardiographic parameters for assessing aortic stenosis (AS) include peak transvalvular jet velocity (Vmax), mean pressure gradient, and aortic valve area (AVA) (ASE, Scientific Statement on Rheumatic Heart Disease, 2023). For accurate Doppler gradient assessment, apical, right parasternal, and suprasternal views are used to achieve parallel alignment of the ultrasound beam with the jet (Manual of Echocardiography for CHD, 2024).
Criteria for Severe AS (ASE, 2023)
Severe AS is suggested by the following values:
| Parameter | Severe AS Threshold |
|---|---|
| Transaortic Vmax | ≥4 m/s |
| Mean Pressure Gradient | ≥40 mmHg |
| AVA | <1 cm² |
| Indexed AVA | <0.6 cm²/m² |
| LVOT/AV Velocity Ratio (DI) | <0.25 |
Grading by CWD Parameters (All Levels of Obstruction)
According to continuous-wave Doppler data, the degree of AS (subvalvular/valvular/supravalvular) is graded as follows (Manual of Echocardiography for CHD, 2024):
| Degree | Peak Velocity (LVOT) | Peak Gradient | Mean Gradient |
|---|---|---|---|
| Mild | 2–3 m/s | <36 mmHg | <20 mmHg |
| Moderate | 3–4 m/s | 36–64 mmHg | 20–40 mmHg |
| Severe | >4 m/s | >64 mmHg | >40 mmHg |
This grading is applicable for patients with normal LV function without associated defects such as VSD (Manual of Echocardiography for CHD, 2024).
Grading by AVA
By valve area, AS is graded as (Manual of Echocardiography for CHD, 2024):
| Degree | AVA |
|---|---|
| Mild | >1.5 cm² |
| Moderate | 1.0–1.5 cm² |
| Severe | <1.0 cm² (<0.6 cm²/m² in children) |
Low-Flow / Low-Gradient Pitfalls
Before confirming peak gradients through the LVOT as truly low, it is necessary to exclude: non-restrictive VSD with left-to-right shunt, large PDA with right-to-left shunt and retrograde flow in the distal aortic arch, and significant LV dysfunction (Manual of Echocardiography for CHD, 2024).
To differentiate low-gradient severe AS, literature suggests determining the true valve area with normal transaortic flow at rest (Chahal NS et al., JACC Cardiovasc Imaging, 2015) and dobutamine stress echocardiography (DSE) for risk stratification (Hayek S et al., JACC Cardiovasc Imaging, 2015; BSE Guideline for AS, 2021).
Indexing in Patients with Obesity and Prostheses
In severe AS, calculation of the indexed aortic valve area is mandatory; in obese individuals, indexing to the ideal body surface area is recommended. The same principle applies when assessing a patient with a valve prosthesis, where high gradients are due to prosthesis size mismatch rather than dysfunction (Assessment of Echocardiographic Parameters in Obesity, 2025).
Frequently asked questions
What thresholds confirm severe AS?
Vmax ≥4 m/s, mean gradient ≥40 mmHg, AVA <1 cm², indexed AVA <0.6 cm²/m², and LVOT/AV velocity ratio <0.25 (ASE, 2023).
What should be excluded before interpreting the gradient as truly low?
Non-restrictive VSD with left-to-right shunt, large PDA with retrograde flow in the distal aortic arch, and significant LV dysfunction (Manual of Echocardiography for CHD, 2024).
Which view provides maximum velocity on CWD?
Apical, right parasternal, and suprasternal views, ensuring parallel alignment of the beam with the jet (Manual of Echocardiography for CHD, 2024).
To what body surface area should AVA be indexed in an obese patient?
To the ideal body surface area; the same principle applies when assessing a patient with a valve prosthesis (publication on EchoCG assessment in obesity, 2025).
What methods assist with low-gradient AS?
Determining the true AVA with normal transaortic flow at rest and dobutamine stress echocardiography (DSE) for risk stratification (BSE Guideline for AS, 2021).