How is aortic stenosis classified according to Vmax (maximum velocity)?

Aortic Stenosis Classification According to Vmax

Aortic stenosis is classified into distinct severity categories based on maximum velocity (Vmax) measurements, with mild AS defined as Vmax 2.0-2.9 m/s, moderate AS as Vmax 3.0-3.9 m/s, and severe AS as Vmax ≥4.0 m/s according to American College of Cardiology guidelines. 1

Detailed Classification System

The comprehensive staging system for aortic stenosis based on Vmax includes:

• Stage A (At risk of AS): Vmax <2.0 m/s

  • Includes patients with bicuspid aortic valve or aortic valve sclerosis without hemodynamically significant obstruction 1

• Stage B (Progressive AS):

  • Mild AS: Vmax 2.0-2.9 m/s (mean pressure gradient <20 mmHg)
  • Moderate AS: Vmax 3.0-3.9 m/s (mean pressure gradient 20-39 mmHg) 1

• Stage C (Asymptomatic severe AS): Vmax ≥4.0 m/s (mean pressure gradient ≥40 mmHg)

  • C1: Normal left ventricular ejection fraction (LVEF)
  • C2: Reduced LVEF 1

• Stage D (Symptomatic severe AS): Vmax ≥4.0 m/s (mean pressure gradient ≥40 mmHg) with symptoms

  • D1: High-gradient severe AS
  • D2: Low-flow, low-gradient severe AS with reduced LVEF
  • D3: Low-gradient severe AS with normal LVEF 1

• Very severe AS: Some research suggests further stratification with Vmax ≥5.0 m/s identifying patients at particularly high risk of mortality 2

Clinical Implications and Measurement Considerations

• Vmax is measured using continuous-wave Doppler echocardiography and should be assessed from multiple acoustic windows to avoid underestimation 1

• The velocity curve shape provides additional diagnostic information:

  • Mild AS: Triangular velocity curve shape
  • Severe AS: Rounded velocity curve shape 1

• Pressure gradients are calculated from velocity using the simplified Bernoulli equation:

  • Maximum gradient: ΔPmax = 4v²
  • Mean gradient: Average of instantaneous gradients over ejection period 1

• Rapid progression of AS is defined as an annual increase in Vmax ≥0.2 m/s 1, 3

Important Caveats and Pitfalls

• Inconsistencies between parameters: Current guidelines show discrepancies between Vmax, mean pressure gradient, and aortic valve area (AVA) cutoffs 4

  • An AVA of 1.0 cm² corresponds to a mean pressure gradient of only 21 mmHg and a Vmax of 3.3 m/s in some studies 4
  • Conversely, Vmax of 4.0 m/s corresponds to an AVA of approximately 0.82-0.92 cm² 5, 4

• Misalignment errors: Improper alignment of the ultrasound beam with the AS jet can significantly underestimate velocity and pressure gradient measurements 1

• Low-flow states: Patients with reduced stroke volume (stroke volume index <35 mL/m²) may have lower Vmax values despite severe stenosis, requiring additional assessment methods 1, 5

  • These patients show higher rates of discrepancy between different severity parameters (40% vs. 16% in normal-flow patients) 5

• Dobutamine stress testing: Recommended in patients with low-flow, low-gradient AS with reduced LVEF (Stage D2) to distinguish true severe AS from pseudo-severe AS 1

• Demographic variations: Progression rates may vary by demographic factors:

  • Men show more rapid progression than women
  • White patients show more rapid progression than African American patients 5