Thread by @GUH_ICU_Anaesth

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Tuesdays Tweetorial:
You are in cardiothoracic theatre doing a mitral valve replacement for severe MR

The anaesthetic consultant is doing a TOE and keeps saying 'PISA'

U know its in Italy but have no idea why he keeps saying it

What is PISA and why is it used?

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PISA = Proximal Isovelocity Surface Area

Blood is ejected -> LA

It converges at the mitral regurgitant orifice it forming hemispheres -> different blood velocity in each hemisphere

RCCs that are equidistant from the orifice(in each hemisphere) travel at similar speed

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Each hemisphere has a radius

The radius that matters for calculations is the one where aliasing occurs (where color changes from blue to red or red to blue)
Remember:
Blue: RCCs moving Away from probe
Red: Towards the probe

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Why does this color change occur?

Color Doppler is similar to pulse wave Doppler so is dependent on US sampling rate

If blood flow is too fast it cannot tell which direction it is flowing in so aliasing occurs

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What is the velocity where aliasing occurs called?

->Nyquist limit = PRF/2

PRF = Pulse repetition frequency = no. of US pulses sent per second

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SO when the Nyquist limit (velocity where aliasing occurs) is exceeded

Blood appears to flow in the opposite direction like the wagon wheel in the old westerns

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Why do we reduce the Nyquist limit to assess MR?

By reducing the velocity where aliasing occurs - we INCREASE the PISA radius

This allows us to measure the radius of the hemisphere more accurately

PISA radius at 50cm/s vs 40cm/s

Radius at 40=MUCH larger

Image from BSE:

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The volume flow rate of the MR jet is calculated:

VRF = 2 x π x r2 x Aliasing velocity

We therefore need to ensure the radius is measured accurately as we SQUARE the result

So a larger radius is easier to measure accurately!

MR can graded using the following equations:

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So now you know

PISA measurement isnt that complicated!
#echofirst