Aortic Stenosis Classification and Management

Classification of AS Severity

The American College of Cardiology and other guidelines classify aortic stenosis 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, 2, 3
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, 3
Stage B (Progressive AS): includes mild AS with Vmax 2.0-2.9 m/s or mean pressure gradient <20 mmHg, and moderate AS with Vmax 3.0-3.9 m/s or mean pressure gradient 20-39 mmHg 1, 3
Stage C (Asymptomatic severe AS): defined as Vmax ≥4 m/s or mean pressure gradient ≥40 mmHg with AVA typically ≤1.0 cm², with subcategories C1 (Normal LVEF) and C2 (Reduced LVEF) 1, 4
Stage D (Symptomatic severe AS): defined as Vmax ≥4 m/s or mean pressure gradient ≥40 mmHg with symptoms, with subcategories D1 (High-gradient), D2 (Low-flow, low-gradient with reduced LVEF), and D3 (Low-gradient with normal LVEF) 1, 4

Vmax is measured using continuous-wave Doppler echocardiography and should be assessed from multiple acoustic windows to avoid underestimation 5, 6
The shape of the velocity curve provides additional diagnostic information, with mild AS showing a triangular shape and severe AS showing a rounded curve 5, 6
Pressure gradients are calculated from velocity using the simplified Bernoulli equation, with maximum gradient calculated as DPmax = 4v² and mean gradient calculated by averaging instantaneous gradients over ejection period 5, 7

Misalignment of the ultrasound beam with the AS jet can significantly underestimate velocity and pressure gradient measurements 7, 6
Low-flow states can lead to lower Vmax values despite severe stenosis, requiring additional assessment methods 1, 4
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, 3, 4
Progression of AS should be monitored, with rapid progression defined as an annual increase in Vmax ≥0.2 m/s 8