What is the difference between Aortic Valve Area (AVA) and indexed Aortic Valve Area (AVAi) in echocardiography (echo)?

Difference Between AVA and AVAi in Echocardiography

The main difference between Aortic Valve Area (AVA) and indexed Aortic Valve Area (AVAi) is that AVA is the absolute measurement of the valve opening in cm², while AVAi is the AVA normalized to body surface area (BSA) in cm²/m², accounting for differences in patient size.

Key Differences and Clinical Significance

Definition and Measurement

• AVA: Absolute measurement of the effective aortic valve opening area, typically measured in cm²
• AVAi: AVA divided by body surface area (BSA), measured in cm²/m²

Diagnostic Thresholds

• AVA: Severe aortic stenosis (AS) is defined as AVA ≤1.0 cm² 1
• AVAi: Severe AS is defined as AVAi ≤0.6 cm²/m² 1

Clinical Implications

• Patient Size Consideration: AVAi accounts for differences in body size, which is particularly important in:

  • Very small patients (where an AVA of 1.0 cm² might be relatively adequate)
  • Large patients (where an AVA of 1.0 cm² might be relatively more stenotic)

• Prevalence Impact: Using AVAi increases the prevalence of patients classified with severe AS compared to using AVA alone 2

  • In one study, prevalence of severe AS increased from 71% to 80% in a retrospective cohort and from 29% to 44% in the SEAS trial when using AVAi instead of AVA 2

Clinical Applications

Staging Aortic Stenosis

Both AVA and AVAi are used in the staging of AS according to ACC/AHA guidelines 1:

• Stage C: Asymptomatic severe AS
  • AVA typically ≤1.0 cm² or AVAi ≤0.6 cm²/m²
• Stage D: Symptomatic severe AS
  • AVA typically ≤1.0 cm² or AVAi ≤0.6 cm²/m²

Low-Flow, Low-Gradient AS

AVAi is particularly useful in assessing patients with:

• Stage D3 AS: Symptomatic severe low-gradient AS with normal LVEF or paradoxical low-flow severe AS
  • Characterized by AVA ≤1.0 cm² with aortic velocity <4 m/s or mean pressure gradient <40 mmHg
  • Indexed AVA ≤0.6 cm²/m² and stroke volume index <35 mL/m² 1

Important Considerations and Pitfalls

Potential Limitations of AVAi

• Overdiagnosis Concern: Using AVAi may lead to classifying some patients with milder disease as having severe AS 2
  • Patients additionally categorized as severe by AVAi experienced significantly fewer valve-related events than those fulfilling only the AVA criterion 2

Measurement Methods

• Both AVA and AVAi can be calculated using:
  • Continuity equation: Most common method using Doppler echocardiography 1
  • Direct planimetry: Anatomic measurement of valve opening 1
  • Cardiac catheterization: Invasive measurement 3

Integrated Assessment

• Neither AVA nor AVAi should be used in isolation:
  • Multiple parameters should be considered, including:
    • Peak velocity (≥4 m/s for severe AS)
    • Mean gradient (≥40 mmHg for severe AS)
    • Valve anatomy and calcification 1

When to Use AVA vs. AVAi

• Use AVA: As primary measurement in average-sized adults
• Use AVAi: When patient size is significantly different from average (very small or large patients)
• Consider both: For comprehensive assessment, especially in borderline cases
• Special situations: In low-flow states (reduced LVEF or paradoxical low-flow), both measurements along with dobutamine stress testing may be necessary 1

AVAi provides additional information by accounting for body size, but it's important to integrate this with other hemodynamic parameters and clinical findings for optimal assessment of aortic stenosis severity.