What are the echocardiogram criteria for diagnosing severe aortic stenosis?

Echocardiographic Criteria for Severe Aortic Stenosis

Severe aortic stenosis is diagnosed when ANY of these three primary hemodynamic parameters is present: aortic valve area (AVA) <1.0 cm², peak jet velocity ≥4.0 m/s, or mean pressure gradient ≥40 mmHg. 1

Primary Hemodynamic Parameters

1. Aortic Valve Area (AVA)

• AVA <1.0 cm² (or indexed AVA ≤0.6 cm²/m²) by continuity equation 1
• Calculation method:
  • AVA = (LVOT area × LVOT VTI) / AV VTI
  • LVOT diameter measured from inner edge to inner edge in parasternal long-axis view in mid-systole
  • LVOT velocity recorded with pulsed Doppler from apical approach

2. Peak Jet Velocity

• Peak velocity ≥4.0 m/s 1
• Must be obtained from multiple acoustic windows
• Use dedicated small dual-crystal CWD transducer for best results
• Report the highest velocity obtained from any window

3. Mean Pressure Gradient

• Mean gradient ≥40 mmHg 1
• Calculated by averaging instantaneous gradients over ejection period
• Cannot be calculated from mean velocity alone

Special Considerations for Low-Flow, Low-Gradient AS

Classical Low-Flow, Low-Gradient AS (with reduced EF)

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• LVEF <50%
• Stroke volume index <35 mL/m² 2
• Requires dobutamine stress echocardiography to differentiate:
  • True severe AS: AVA remains <1.0 cm² with flow normalization
  • Pseudosevere AS: AVA increases to >1.0 cm² with increased flow 2
• Flow reserve defined as increase in stroke volume ≥20% 1

Paradoxical Low-Flow, Low-Gradient AS (with preserved EF)

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• LVEF ≥50%
• Stroke volume index <35 mL/m² 2
• Echocardiographic findings:
  • Small, hypertrophied LV cavity
  • Concentric LV remodeling
  • Reduced LV longitudinal function 2

Additional Parameters to Consider

Valve Calcification

• Cardiac CT calcium scoring helpful in low-flow, low-gradient cases:
  • Severe AS likely: ≥2000 Agatston units in men, ≥1200 in women
  • Severe AS very likely: ≥3000 Agatston units in men, ≥1600 in women
  • Severe AS unlikely: <1600 Agatston units in men, <800 in women 1

Dimensionless Index (DI)

• DI = LVOT velocity / AV velocity
• DI <0.25 suggests severe AS
• Less affected by flow conditions than AVA

Common Pitfalls and Technical Considerations

1. Misalignment of Doppler beam

   • Use multiple acoustic windows to obtain highest velocity
   • Underestimation of velocity is the most common error 1

2. LVOT diameter measurement errors

   • Measure in mid-systole from inner edge to inner edge
   • Elliptical shape of LVOT may lead to underestimation of AVA
   • Consider 3D TEE or MSCT for more accurate LVOT area 1

3. Flow status assessment

   • Normal flow: SVi ≥35 mL/m²
   • Low flow: SVi <35 mL/m² 1
   • Hypertension can cause pseudo-normalization of gradients 2

4. Inconsistency between criteria

   • AVA of 1.0 cm² typically corresponds to mean gradient of only ~21 mmHg 3
   • Discordance more common in women and patients with reduced stroke volume 4
   • When discordant, evaluate valve calcification and consider flow status 1

5. Aorto-mitral angle

   • Narrower angles may lead to AVA-Doppler discordance in low-gradient AS 5
   • Consider alternative imaging when discordance is present

Integrated Approach to Diagnosis

1. Confirm valve morphology showing thickening, calcification, reduced motion
2. Measure peak velocity and mean gradient from multiple windows
3. Calculate AVA using continuity equation
4. Assess flow status (normal vs. low flow)
5. Evaluate LV function (preserved vs. reduced EF)
6. Consider additional testing when criteria are discordant:
   • Dobutamine stress echocardiography (for low EF)
   • CT calcium scoring (especially for preserved EF)

Remember that patients with AVA ≤0.6 cm² represent a particularly high-risk subgroup with significantly worse outcomes, even when asymptomatic 6.