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Why aortic dilation occur in aortic stenosis

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"aortic valve stenosis" AND "aortic dilatation"

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aortic stenosis ascending aortic dilatation mechanism bicuspid valve authoritative

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Aortic dilatation in aortic stenosis is usually due to two related mechanisms:
  1. Post-stenotic jet injury
    • The narrowed valve produces a high-velocity, turbulent systolic jet.
    • This jet strikes the wall of the proximal ascending aorta, increasing shear stress and causing gradual remodeling and enlargement just beyond the valve, called post-stenotic dilatation.
  2. Underlying aortopathy, especially with a bicuspid aortic valve
    • Many younger patients with aortic stenosis have a bicuspid aortic valve.
    • Bicuspid valve disease is associated with an intrinsically abnormal aortic wall, involving altered extracellular matrix and reduced elastic integrity.
    • Therefore, the ascending aorta may dilate even when stenosis is not severe. It is not only a pressure or flow problem.
So the key distinction is:
  • Calcific tricuspid aortic stenosis: dilation is more often mainly related to the eccentric turbulent jet and chronic wall stress.
  • Bicuspid aortic stenosis: dilation reflects both abnormal eccentric flow and an inherent tendency of the aortic wall to enlarge.
This is why echocardiography, CT, or MRI in aortic stenosis should measure the aortic root and ascending aorta, particularly when a bicuspid valve is present. Textbooks describe post-stenotic dilatation with AS, and note that bicuspid valves can cause dilatation disproportionate to the severity of valve dysfunction. ACC/AHA aortic disease guideline supports surveillance of the aorta in bicuspid aortic-valve disease.

Doesn't the blood flow loses energy beyond valve

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aortic stenosis jet poststenotic dilatation pressure recovery mechanism

Yes. Some of the energy is lost beyond a stenotic valve, mainly as heat and turbulence. But that energy loss is also part of why the aortic wall can be affected.
Sequence:
  1. At the narrowed valve, blood must accelerate sharply to maintain flow. Its velocity and kinetic energy rise greatly.
  2. Immediately beyond the valve, the jet is narrow, eccentric, and turbulent. It can strike a particular region of the ascending-aortic wall, producing high local shear stress and fluctuating wall forces.
  3. Farther downstream, the jet disperses and much of its kinetic energy is dissipated as turbulence and heat. Some kinetic energy also converts back to pressure, termed pressure recovery.
So, dilation is not because high energy persists uniformly throughout the whole aorta. It is because the localized, repetitive impact and shear from the high-velocity jet close to the valve can promote wall remodeling before the jet's energy has fully dissipated.
In bicuspid aortic valve disease, the jet is often particularly eccentric, and the aortic wall may be intrinsically prone to dilation. Thus even if energy is ultimately lost downstream, the ascending aorta receives repeated focal mechanical stress. A study of bicuspid AS describes the high-velocity jet increasing shear stress on the anterolateral ascending aorta in this setting: Circulation study.
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