SEVERE AORTIC STENOSIS: THE GRADIENT CAN BE MISLEADING An aortic valve area ≤1.0 cm² suggests severe aortic stenosis (AS), but the mean gradient may be below 40 mmHg. The gradient depends on blood flow, not just valve narrowing. 1. High-gradient AS - AVA ≤1.0 cm² - Mean gradient ≥40 mmHg - Usually preserved or reduced LVEF 2. Classical low-flow, low-gradient AS - AVA ≤1.0 cm² - Mean gradient <40 mmHg - LVEF <50% - Stroke volume index ≤35 mL/m² 3. Paradoxical low-flow, low-gradient AS - AVA ≤1.0 cm² - Mean gradient <40 mmHg - LVEF ≥50% - Stroke volume index ≤35 mL/m² 4. Normal-flow, low-gradient AS - AVA ≤1.0 cm² - Mean gradient <40 mmHg - LVEF ≥50% - Stroke volume index >35 mL/m² Why this matters: Low flow can conceal the hemodynamic severity of a stenotic valve. Discordant findings require careful assessment of Doppler measurements, blood pressure, flow state and valve anatomy. In classical low-flow AS, dobutamine stress echocardiography can help distinguish true severe from pseudo-severe AS. CT aortic valve calcium scoring can help when severity remains uncertain. Clinical pearl: Never grade AS using the valve area or gradient alone. Integrate AVA, mean gradient, peak velocity, stroke volume, LVEF and clinical context. Reference: 2025 ESC/EACTS Guidelines for the Management of Valvular Heart Disease.