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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 !

Vena contracta* Who named it     http://en.wikipedia.org/wiki/Vena_contracta

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 ?

Final message

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  . . .


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