What are the echocardiographic criteria for diagnosing aortic stenosis?

Echocardiographic Criteria for Aortic Stenosis

Severe aortic stenosis is diagnosed when peak jet velocity is ≥4 m/s, mean gradient is ≥40 mmHg, or aortic valve area (AVA) is <1.0 cm², though these three parameters must be interpreted together as they can be inconsistent, particularly in low-flow states. 1

Primary Hemodynamic Parameters

The three essential measurements for AS severity assessment are: 1, 2

Peak Jet Velocity

• ≥4.0 m/s indicates severe AS 1, 2
• 3.0-4.0 m/s indicates moderate AS 2
• 2.6-2.9 m/s indicates mild AS 2
• Must be obtained from multiple acoustic windows using a dedicated small dual-crystal continuous-wave Doppler transducer 1
• Beam misalignment is a major source of error—interrogate from apical, right parasternal, suprasternal, and subcostal windows 1

Mean Transvalvular Pressure Gradient

• ≥40 mmHg indicates severe AS 1, 2
• 20-40 mmHg indicates moderate AS 2
• <20 mmHg indicates mild AS 2
• Must be calculated by averaging instantaneous gradients over the ejection period, not from mean velocity 1

Aortic Valve Area (AVA)

• <1.0 cm² indicates severe AS 1, 2
• 1.0-1.5 cm² indicates moderate AS 2

• 1.5 cm² indicates mild AS 2

• Calculated using the continuity equation: AVA = (CSA_LVOT × VTI_LVOT) / VTI_AV 1

Critical Technical Considerations for AVA Calculation

LVOT Diameter Measurement

• Measure in parasternal long-axis view in mid-systole 1
• Measure from inner edge to inner edge of septal endocardium and anterior mitral leaflet 1
• Major limitation: Assumes circular LVOT shape, but it's actually elliptical, leading to underestimation of flow and AVA 1
• Consider 3D TEE or MSCT for direct LVOT planimetry when measurements are discordant 1

LVOT Velocity Measurement

• Record with pulsed Doppler from apical approach (five-chamber or apical long-axis view) 1
• Position sample volume just proximal to aortic valve (0.5-1.0 cm below if flow acceleration occurs at annulus) 1
• Obtain smooth velocity curve without spectral dispersion 1

Integrated Stepwise Approach to Severity Grading

Step 1: Assess Valve Morphology

• Identify thickening, calcification, reduced cusp motion (calcific AS), doming (congenital AS), or fused commissures (rheumatic AS) 1

Step 2: Determine Gradient Category

• High gradient (velocity ≥4 m/s or mean gradient ≥40 mmHg): Generally confirms severe AS without further testing needed 1
• Low gradient (mean gradient <40 mmHg): Requires additional evaluation with AVA and flow assessment 1

Step 3: For Low Gradient AS—Assess Flow Status

Calculate stroke volume index (SVi): 1

• Normal flow: SVi ≥35 mL/m²
• Low flow: SVi <35 mL/m²

Step 4: Classify Based on Flow and EF

Low Flow, Low Gradient with Reduced EF (<50%): 1

• Perform low-dose dobutamine stress echo (DSE) to distinguish true severe from pseudosevere AS 1, 2
• Increase in AVA to >1.0 cm² suggests pseudosevere AS 1
• Severe AS confirmed if velocity ≥4 m/s or mean gradient >30-40 mmHg with AVA remaining <1.0 cm² at any flow rate 1
• Absence of contractile reserve (failure to increase SV by >20%) predicts high surgical mortality but valve replacement may still benefit 1

Low Flow, Low Gradient with Preserved EF (≥50%)—"Paradoxical" Low Flow AS: 1

• Most challenging diagnosis—requires careful exclusion of measurement errors 1
• Confirm with: 1
  • Mean gradient 30-40 mmHg (when normotensive)
  • AVA ≤0.8 cm²
  • Low flow confirmed by alternative techniques (3D TEE, MSCT, CMR)
  • Calcium score by MSCT is critical:
    • Severe AS likely: men ≥2000, women ≥1200 Agatston units
    • Severe AS very likely: men ≥3000, women ≥1600
    • Severe AS unlikely: men <1600, women <800

Important Pitfalls and Caveats

Inconsistency of Criteria

• Critical caveat: The three primary parameters are often inconsistent 3, 4
• AVA of 1.0 cm² actually corresponds to mean gradient of only 21-32 mmHg and velocity of 3.3-3.7 m/s in real-world cohorts 3, 4
• Conversely, mean gradient of 40 mmHg corresponds to AVA of 0.75-0.89 cm², and velocity of 4.0 m/s corresponds to AVA of 0.82-0.92 cm² 3, 4
• Discrepancy rate is 40% in low-flow states versus 16% in normal flow 4

High Flow States (SVi >58 mL/m²)

• May produce high gradients even with AVA >1.0 cm² 1
• Identify reversible causes: anemia, hyperthyroidism, arteriovenous shunts, significant aortic regurgitation 1
• Reassess after treating reversible conditions 1

Serial Measurements

• Always record from the same acoustic window where highest velocities obtained 1
• LVOT diameter rarely changes in adults—consider using same measurement to reduce variability 1

Additional Severity Parameters

Beyond the primary three parameters: 2

• Indexed AVA: <0.6 cm²/m² indicates severe AS
• Velocity ratio (LVOT velocity/AV velocity): <0.25 indicates severe AS

Follow-up Intervals

Based on severity: 2, 5

• Severe AS (asymptomatic): Every year
• Moderate AS: Every 1-2 years
• Mild AS: Every 3-5 years
• Aortic sclerosis: Every 3-5 years