Why vena contracta is not measured in mitral stenosis ?
Posted Aug 03 2010 7:55am
Echocardiography is about 50 years old tool.It has evolved from simple M mode to sophisticated tissue Doppler and 4D imaging. Color Doppler imaging was a great revolution ( One can consider it as big as invention of ultrasound itself !)
Even though , we could code the pulse Doppler samples into color coded pixels (Called auto correlation computed by Fourier algorithm) the full potential of color Doppler is yet to be explored. Accurate assessment of regurgitation lesion severity continue to trouble us .
The PISA concept fizzled out due it’s complexity and inaccuracy.It exhausted thousands of cardiology man hours and precious academic time ! (Not really waste . . .it stimulated our intellect !)
I wonder we have a method to predict early ”The would be failed concepts” in medicine !
Suddenly common sense struck us . . . simplicity replaced complexity . The concept of vena contracta came in to vogue.
It is a simple estimate of the narrowest part of a regurgitant jet.It is good enough to assess the severity of regurgitation .The diameter is measured in the zoomed up view of the leaky valve aided by color flow. If it is > 6mm it is severe regurgitation .(Both AR/MR)
Please note ,it is one of the measurement we take in the dimensional regurgitant shell of (blood dome ) in the PISA method . The harrowing exercise of calculating ERO with all those radius and velocity etc may be fresh in many minds !
Can’t we extend the simplicity of the concept of vena contracta further ?
As usual , we assume many things in medicine .
Here the concept of Vena contracta(VC) requires
The orifice is near circular. (Very unlikely , considering the complex shape of mitral valve especially in diseased state)
The vena contracta applies only to single jet MR
Central jet (Eccenticity increase the chances altering the shape of ERO )
but, the major advantage is VC is not much influenced by loading conditions .And the parameter used as such without amplifying the error.
Why vena contracta is not used to assess mitral stenosis severity ?
I wonder why it shoudn’t ? The same principles apply, the flow through narrowest point of mitral valve will reflect the degree of narrowing. In fact ,the inter-leaflet distance could be same as vena contracta in mitral stenosis.
If we assume ! the orifice as a circle, then 50 % the vena contracta is the radius the orifice and ERO can be easily arrived .
Logically yes. We need to validate the data ,comparing with a gold standard .When there is no gold standard , and what we are testing is better than gold standard what shall we do ?
Complex measurements lead to complex errors (Lesson learnt from PISA) , with simple parameters errors do not get amplified.
Do not ditch any investigation just because it is simple . . .