1/9
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?
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?
2/9
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
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
3/9
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
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
4/9
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
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
5/9
What is the velocity where aliasing occurs called?
->Nyquist limit = PRF/2
PRF = Pulse repetition frequency = no. of US pulses sent per second
What is the velocity where aliasing occurs called?
->Nyquist limit = PRF/2
PRF = Pulse repetition frequency = no. of US pulses sent per second
6/9
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
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
7/9
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:
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:
8/9
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:
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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