A mean gradient under 40 mmHg does not exclude severe aortic stenosis. If the valve area is 1.0 cm² or less but the gradient is low, the question is whether flow is low.
With a reduced ejection fraction (classical low-flow, low-gradient), low-dose dobutamine echocardiography separates true severe stenosis, where the gradient rises while the valve area stays small, from pseudo-severe stenosis, where the valve opens further as flow increases. Lack of contractile reserve does not by itself rule out benefit from valve replacement.
With a preserved ejection fraction (paradoxical low-flow), think of the small, hypertrophied ventricle of an older hypertensive patient. A stroke volume index under 35 mL/m² supports low flow, and a CT calcium score of the valve helps confirm severity.
Measurement error is the commonest cause of discordant numbers, so check the outflow tract diameter before reaching conclusions.
- Check stroke volume index when valve area and gradient disagree
- Request dobutamine echocardiography for low gradient with reduced ejection fraction
- Consider CT valve calcium scoring for low gradient with preserved ejection fraction
- Recheck the outflow tract measurement first; it is the usual source of discordance
Why it matters
Patients with low-flow severe stenosis are easy to miss and do badly without valve replacement.
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