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How is LV Aorta pressure gradient generated in aortic stenosis

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aortic stenosis left ventricular aortic pressure gradient mechanism

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In aortic stenosis, the narrowed, rigid valve opening creates a fixed obstruction to systolic ejection.
During LV systole:
  1. The LV must raise its pressure above aortic pressure to force blood through the small valve orifice.
  2. Blood accelerates markedly as it passes through the narrowed valve, forming a high-velocity jet.
  3. Energy is required to accelerate the flow and overcome friction/turbulence across the stenotic valve. This energy loss appears as a pressure drop distal to the valve.
  4. Therefore, at the same instant in systole:
    LV pressure > proximal aortic pressure, creating the LV-to-aorta transvalvular pressure gradient.
The tighter the stenosis and the higher the transvalvular flow, the larger the gradient. Doppler estimates the instantaneous gradient using the simplified Bernoulli equation:
[ \Delta P = 4V^2 ]
where (V) is the peak aortic jet velocity in m/s. Thus, a jet velocity of 4 m/s corresponds to a peak instantaneous gradient of about (4 \times 4^2 = 64) mmHg.
Two practical points:
  • The gradient is flow-dependent. It increases with higher stroke volume, exercise, or tachycardia and may be low despite severe stenosis when LV output is reduced.
  • Doppler peak instantaneous gradient is not the same as catheter peak-to-peak gradient, because peak LV and peak aortic pressures occur at different times.
The sustained LV pressure overload causes concentric LV hypertrophy as compensation. [Textbook of Clinical Echocardiography, p. 337]
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