Summary: This phenomenon is only normally an issue if the aorta is <30mm diameter. The overall effect is an overestimation of pressure differences
Pressure precovery is a slippery concept that relates to an inaccuracy that can be seen with CWD measurement of AS severity vs. direct LV catheterisation using a pressure wire. Overall use of doppler echocardiography tends to overestimate pressure gradients through a stenotic valve compared to the “true” pressure gradient measured via pressure wire.
Explanation
LV peak velocity and Aorta peak velocity occur at different times in the cardiac cycle.
CWD measurement may overestimate true velocity, especially in individuals with small ascending aorta diameters.
Potential energy is converted to kinetic energy through the stenotic lesion where velocity increases and a pressure drop occurs (Bernoulli effect).
Distal to the stenosis flow deccelerates again as the aorta widens. Some energy is lost to heat and sound (audible murmur) BUT some energy is "Recovered" back into potential energy.
Pressure recovery is determined by the ratio between:
- EoA (Effective orifice valve area by continuity equation)
- Aoa (Aortic area distal to the stenosis)\
Generally speaking AS has an abrupt change in geometry from the stenotic area to the wide aortic region. This is unfavourable for significant pressure recovery to develop. Instances where pressure recovery can be problematic are when aortic dimensions are small and a more tapered transition from the stenotic area to the aorta is seen i.e. aorta diameter <30mm. Likely to be seen in congenital AS cases and small female patients.
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