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

Aortic Stenosis Classification According to Vmax

Aortic stenosis (AS) is classified into distinct stages based on maximum velocity (Vmax), with severe AS defined as Vmax ≥4 m/s, moderate AS as Vmax 3.0-3.9 m/s, and mild AS as Vmax 2.0-2.9 m/s. 1

Classification of AS Severity by Vmax

• Stage A (At risk of AS): Vmax <2 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 or mean pressure gradient <20 mmHg 1
  • Moderate AS: Vmax 3.0-3.9 m/s or mean pressure gradient 20-39 mmHg 1

• Stage C (Asymptomatic severe AS):

  • C1 (Normal LVEF): Vmax ≥4 m/s or mean pressure gradient ≥40 mmHg with AVA typically ≤1.0 cm² 1
  • C2 (Reduced LVEF): Vmax ≥4 m/s or mean pressure gradient ≥40 mmHg with AVA typically ≤1.0 cm² and LVEF <50% 1

• Stage D (Symptomatic severe AS):

  • D1 (High-gradient): Vmax ≥4 m/s or mean pressure gradient ≥40 mmHg with symptoms 1
  • D2 (Low-flow, low-gradient with reduced LVEF): AVA ≤1.0 cm² with Vmax <4 m/s or mean pressure gradient <40 mmHg, LVEF <50% 1
  • D3 (Low-gradient with normal LVEF): AVA ≤1.0 cm² with Vmax <4 m/s or mean pressure gradient <40 mmHg, stroke volume index <35 mL/m² 1

Very Severe AS Considerations

• Vmax ≥5 m/s indicates very severe AS with significantly increased mortality risk, even in asymptomatic patients 2
• US guidelines consider Vmax ≥5 m/s as very severe AS, while European guidelines use a threshold of ≥5.5 m/s 2
• Patients with Vmax ≥5 m/s have significantly higher mortality compared to those with Vmax <5 m/s, regardless of symptom status 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 shape of the velocity curve provides additional diagnostic information:

  • Mild AS: Triangular shape with peak in early systole 1
  • Severe AS: Rounded curve with peak moving toward mid-systole 1

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

  • Maximum gradient: DPmax = 4v² 1
  • Mean gradient: Calculated by averaging instantaneous gradients over ejection period 1

Important Caveats and Pitfalls

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

• Low-flow states can lead to lower Vmax values despite severe stenosis, requiring additional assessment methods 1

• In patients with low-flow, low-gradient AS with reduced LVEF (Stage D2), dobutamine stress testing is recommended to distinguish true severe AS from pseudo-severe AS 1

• Inconsistencies between Vmax, mean gradient, and AVA criteria are common:

  • An AVA of 1.0 cm² correlates with a mean gradient of approximately 21 mmHg and Vmax of 3.3 m/s in some studies 3
  • A Vmax of 4.0 m/s corresponds to an AVA of approximately 0.82 cm² 3

• Progression of AS should be monitored, with rapid progression defined as an annual increase in Vmax ≥0.2 m/s 1, 4

• Patients with moderate-to-severe valve calcification and higher baseline Vmax show more rapid progression and worse outcomes 4, 5