What are the echocardiography (echo) parameters for grading aortic valve stenosis?

Echocardiographic Parameters for Grading Aortic Valve Stenosis

The primary echocardiographic parameters for grading aortic valve stenosis severity are peak jet velocity (≥4.0 m/s), mean transvalvular pressure gradient (≥40 mmHg), and aortic valve area (<1.0 cm²) by continuity equation, with any of these criteria indicating severe stenosis when present. 1

Primary Hemodynamic Parameters

1. Peak Jet Velocity

• Mild AS: 2.6-2.9 m/s
• Moderate AS: 3.0-4.0 m/s
• Severe AS: ≥4.0 m/s 1

2. Mean Transvalvular Pressure Gradient

• Mild AS: <20 mmHg
• Moderate AS: 20-40 mmHg
• Severe AS: ≥40 mmHg 1

3. Aortic Valve Area (AVA) by Continuity Equation

• Mild AS: >1.5 cm²
• Moderate AS: 1.0-1.5 cm²
• Severe AS: <1.0 cm² 1

4. Indexed AVA (for Body Surface Area)

• Mild AS: >0.85 cm²/m²
• Moderate AS: 0.60-0.85 cm²/m²
• Severe AS: <0.60 cm²/m² 1

5. Velocity Ratio (LVOT velocity/Aortic jet velocity)

• Mild AS: >0.50
• Moderate AS: 0.25-0.50
• Severe AS: <0.25 1

Technical Considerations for Accurate Measurement

1. Peak Jet Velocity:

   • Must be obtained from multiple acoustic windows
   • Use a dedicated small dual-crystal CWD transducer
   • Align the ultrasound beam with the direction of blood flow 1

2. Mean Gradient:

   • Calculate by averaging instantaneous gradients over ejection period
   • Cannot be calculated from mean velocity
   • Requires proper beam alignment to avoid underestimation 1

3. AVA Calculation:

   • LVOT diameter: Measure from inner edge to inner edge in parasternal long-axis view in mid-systole
   • LVOT velocity: Record with pulsed Doppler from apical approach
   • Position sample volume just proximal to aortic valve
   • Consider 3D imaging (TEE or MSCT) to account for elliptical LVOT shape 1

Discordant Grading Patterns

Low-Flow, Low-Gradient AS with Reduced EF (<50%)

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• EF <50%
• Stroke volume index <35 mL/m² 1

Management approach:

• Perform dobutamine stress echocardiography
• Look for contractile reserve (increase in SV ≥20%)
• True severe AS: AVA remains <1.0 cm² with increased flow
• Pseudosevere AS: AVA increases to >1.0 cm² with increased flow 1

Low-Flow, Low-Gradient AS with Preserved EF (≥50%)

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• EF ≥50%
• Stroke volume index <35 mL/m² 1

Additional criteria suggesting severe AS:

• Clinical: Symptoms, elderly patient (>70 years)
• Imaging: LVH, reduced longitudinal function
• Calcium score by MSCT: ≥3000 AU in men, ≥1600 AU in women 1

Normal-Flow, Low-Gradient AS

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• Stroke volume index ≥35 mL/m²
• Most likely represents moderate AS or measurement error 1

Common Pitfalls and Solutions

1. Underestimation of gradient:

   • Poor Doppler alignment with flow direction
   • Solution: Use multiple acoustic windows to capture highest velocity 1

2. LVOT diameter measurement errors:

   • Underestimation of LVOT area leads to underestimation of AVA
   • Solution: Careful measurement technique, consider 3D imaging 1

3. Inconsistency between criteria:

   • An AVA of 1.0 cm² typically corresponds to a mean gradient of only 21 mmHg, not 40 mmHg 2
   • Solution: Integrate all parameters and clinical data 1

4. Hypertension:

   • Can alter peak velocity/mean gradient
   • Solution: Record blood pressure during examination; ideally evaluate when BP is normal 1

Integrated Approach to AS Assessment

1. Assess valve morphology (thickening, calcification, reduced motion)
2. Measure peak velocity and mean gradient using proper technique
3. Calculate AVA using continuity equation
4. Determine flow status (normal vs. low flow)
5. Assess LV function (preserved vs. reduced EF)
6. Consider calcium scoring by CT in cases of discordant grading 1

When findings are discordant between AVA and gradient measurements, carefully exclude technical errors and consider additional imaging modalities such as CT calcium scoring to confirm true AS severity 1, 3.