How is aortic stenosis graded by valve area in older adults?

Aortic Stenosis Grading by Valve Area

Severe aortic stenosis is defined by an aortic valve area (AVA) <1.0 cm², moderate stenosis by AVA 1.0-1.5 cm², and mild stenosis by AVA >1.5 cm², with indexed AVA <0.6 cm²/m² used for small adults, children, and adolescents. 1

Standard Valve Area Thresholds

The classification system uses absolute AVA measurements as the primary criterion 1:

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

These thresholds apply to the effective orifice area calculated by the continuity equation, not the anatomic area, as the effective area is significantly smaller due to flow contraction and serves as the primary predictor of clinical outcomes 1.

Body Size Indexation

Indexed AVA should be calculated as AVA/body surface area (BSA) with a threshold of <0.6 cm²/m² defining severe stenosis, but this is primarily important in children, adolescents, and small adults—not routinely in obese patients. 1, 2

The rationale for selective indexation 1:

• Valve area does not increase proportionally with excess body weight 1
• Current BSA algorithms do not accurately reflect normal AVA in obese patients 1
• Without indexation, valve area may appear falsely severe in small-bodied individuals 1

A critical pitfall: Using indexed AVA universally can misclassify obese patients as having more severe disease than actually present 1. Recent evidence suggests indexing to height (AVA/H <0.6 cm²/m) may provide better correlation across body morphologies than BSA indexation, particularly in obese populations 3.

Integration with Other Hemodynamic Parameters

Any single criterion—AVA <1.0 cm², peak velocity ≥4.0 m/s, or mean gradient ≥40 mmHg—can indicate severe AS, but concordance among all three provides the most reliable diagnosis. 1, 2

When measurements are concordant, classification is straightforward 1. However, discordance requires careful evaluation:

High-Flow Situations

• AVA may be >1.0 cm² despite velocity ≥4 m/s and gradient ≥40 mmHg when transvalvular flow is elevated 1
• This occurs with concomitant aortic regurgitation or high cardiac output states (fever, anemia, hyperthyroidism, dialysis shunts) 1
• The hemodynamics still reflect severe LV pressure overload despite larger valve area 1

Low-Flow, Low-Gradient Scenarios

When AVA <1.0 cm² but velocity <4 m/s and gradient <40 mmHg, measurement errors must be excluded first—particularly underestimation of LVOT area, which is the most common technical error leading to falsely low calculated valve areas. 1, 2

After excluding technical errors, further classification depends on ejection fraction and flow status 1, 2:

Low-Flow, Low-Gradient with Reduced EF (Stage D2) 1:

• AVA <1.0 cm²
• Mean gradient <40 mmHg
• LVEF <50%
• Stroke volume index <35 mL/m²
• Requires dobutamine stress echo to distinguish true-severe (AVA remains ≤1.0 cm² with velocity rising to ≥4 m/s) from pseudo-severe AS 1, 4, 2

Low-Flow, Low-Gradient with Preserved EF (Stage D3) 1, 2:

• AVA <1.0 cm² (ideally ≤0.8 cm²)
• Mean gradient 30-40 mmHg (measured when normotensive)
• LVEF ≥50%
• Stroke volume index <35 mL/m²
• Typically elderly patients with hypertrophied, small ventricles 1
• CT calcium scoring becomes critical: men ≥2000 Agatston units and women ≥1200 units suggest severe AS; men ≥3000 and women ≥1600 make it very likely 1, 5

Clinical Decision Algorithm

When evaluating valve area measurements 1, 2:

1. Verify measurement technique: Ensure LVOT diameter is measured correctly (most common error source), Doppler alignment is optimal, and patient is normotensive 1, 2

2. Check concordance: Compare AVA with velocity and gradient 1, 2

3. If discordant with AVA <1.0 cm² but low gradients:

   • Assess flow state using stroke volume index (threshold 35 mL/m²) 1
   • Consider indexed AVA if patient has extreme body size 1
   • Perform dobutamine stress echo if LVEF <50% 1, 4
   • Obtain CT calcium scoring if LVEF preserved 1, 5

4. If discordant with AVA >1.0 cm² but high gradients: Evaluate for high-flow states and exclude reversible causes before concluding severe AS 1

Important Caveats

Blood pressure must be recorded at every examination, as hypertension artificially elevates velocity and gradient measurements. 1, 2 Ideally, assess AS severity when the patient is normotensive 1.

The velocity ratio (LVOT velocity/aortic jet velocity) <0.25 also indicates severe AS and is less dependent on flow state, though less commonly used in clinical practice 1, 2.

Patients with AVA 0.8-0.99 cm² represent a heterogeneous group—those with normal-flow, low-gradient patterns may have outcomes similar to moderate AS initially, while those with high gradients or low flow behave like AVA <0.8 cm² 6. This supports maintaining the 1.0 cm² threshold rather than lowering it to 0.8 cm² 6.