PProximal roximal

IIsovelocitysovelocity SSurface urface

AArearea

Dr. Sehran BhattiDr. Sehran Bhatti

Regurgitant volumes can be estimated by Regurgitant volumes can be estimated by 2 methods2 methods Volumetric methodVolumetric method PISA methodPISA method

As we knowAs we know Flow rate = CSA x VelocityFlow rate = CSA x Velocity Volume = CSA x TVIVolume = CSA x TVI

If regurgitant orifice area is known then If regurgitant orifice area is known then reguritant volume can be estimated as the reguritant volume can be estimated as the product of effective regurgitant orifice product of effective regurgitant orifice area (ERO) and regurgitant TVIarea (ERO) and regurgitant TVI

To estimate ERO, Proximal isovelocity To estimate ERO, Proximal isovelocity surface area is usedsurface area is used

RV = ERO x Regurgitant TVIRV = ERO x Regurgitant TVI

As blood flow converges towards the As blood flow converges towards the regurgitant orifice, blood flow velocity regurgitant orifice, blood flow velocity increases with formation of multiple shells of increases with formation of multiple shells of isovelocity of hemispheric shapeisovelocity of hemispheric shape

Remember that velocity of the shell closest Remember that velocity of the shell closest to the regurgitant orifice is highest and vice to the regurgitant orifice is highest and vice versaversa

The flow rate at the surface of a hemispheric The flow rate at the surface of a hemispheric shell with the same flow velocity is shell with the same flow velocity is considered equal to the flow rate across the considered equal to the flow rate across the regurgitant orifice according to the law of regurgitant orifice according to the law of conservation of flow which states thatconservation of flow which states that

““What comes in must go out”What comes in must go out”

By adjusting the Nyquist limit of the color flow By adjusting the Nyquist limit of the color flow map, the flow velocity of a hemispheric surface map, the flow velocity of a hemispheric surface proximal to the regurgitant orifice can be proximal to the regurgitant orifice can be determineddetermined

For e.g. in MR the regurgitant flow travels away For e.g. in MR the regurgitant flow travels away from the position of the apical transducer ans so from the position of the apical transducer ans so the blood converging towards the mitral the blood converging towards the mitral regurgitant orifice in the LV is color coded blue regurgitant orifice in the LV is color coded blue until the velocity reaches the negative aliasing until the velocity reaches the negative aliasing velocity of the selected color flow map, at which velocity of the selected color flow map, at which time the flow will change color to light orange- red time the flow will change color to light orange- red

If the negative aliasing velocity of the color map is If the negative aliasing velocity of the color map is reduced further, the trasition from blue to reduced further, the trasition from blue to orange-red will occur farther from the regurgitant orange-red will occur farther from the regurgitant orifice providing a larger hemispheric shell radiusorifice providing a larger hemispheric shell radius

After a hemisphere with blood flow of After a hemisphere with blood flow of isovelocity is identified the flow rate isovelocity is identified the flow rate through this hemispheric shell is through this hemispheric shell is determined bydetermined by

Flow rate = CSA x VelocityFlow rate = CSA x Velocity

Area of hemispheric shell = 2Area of hemispheric shell = 2ππr², where pie=3.14r², where pie=3.14

Flow rate = 6.28 x r² x Aliasing velocity (from color map)Flow rate = 6.28 x r² x Aliasing velocity (from color map)

As we have already discussed the flow As we have already discussed the flow rate at the surface of a hemispheric shell rate at the surface of a hemispheric shell with the same flow velocity is considered with the same flow velocity is considered equal to the flow rate across the equal to the flow rate across the regurgitant orifice according to the law of regurgitant orifice according to the law of conservation of flow conservation of flow

Therefore, this flow across PISA is equal to Therefore, this flow across PISA is equal to flow rate across EROflow rate across ERO

Flow rate = ERO x regurgitant velocity Flow rate = ERO x regurgitant velocity

ERO = flow rate / peak MR velocityERO = flow rate / peak MR velocity

ERO = 6.28 x r² x Aliasing velocity / MR velocityERO = 6.28 x r² x Aliasing velocity / MR velocity

Regurgitant Volume = ERO x MR TVIRegurgitant Volume = ERO x MR TVI

Substituting value of ERO we getSubstituting value of ERO we get

Regurg Vol = 6.28 x r² x Regurg Vol = 6.28 x r² x Aliasing velocityAliasing velocity x MRTVI x MRTVI MR velocityMR velocity

The concept of PISA can also be applied to The concept of PISA can also be applied to calculate the area of stenotic surfaces and calculate the area of stenotic surfaces and has been validated for MV area in patients has been validated for MV area in patients with mitral stenosiswith mitral stenosis

CaveatsCaveats Proximal to a stenotic mitral orifice, PISA Proximal to a stenotic mitral orifice, PISA

may not be a complete hemisphere but a may not be a complete hemisphere but a portion of hemisphere because of mitral portion of hemisphere because of mitral leaflets geometry on the atrial sideleaflets geometry on the atrial side

In such cases an angle correction factor is In such cases an angle correction factor is appliedapplied

MVA = 6.28 x r² x MVA = 6.28 x r² x Aliasing velocityAliasing velocity x x alphaalpha°° Peak MS velocity 180Peak MS velocity 180°°

Where alpha is the angle between two mitral leaflets on the atrial sideWhere alpha is the angle between two mitral leaflets on the atrial side

Sometimes it is difficult to know in which direction Sometimes it is difficult to know in which direction the baseline should be shifted for optimal PISAthe baseline should be shifted for optimal PISA

For this rule of the thumb is to shift the For this rule of the thumb is to shift the baseline in the direction of the flow jet of baseline in the direction of the flow jet of interestinterest

PISA radius needs to be measured at the same PISA radius needs to be measured at the same time as the peak velocity of the jet time as the peak velocity of the jet

Color M-mode can help in measuring the Color M-mode can help in measuring the radius reliably at the correct timeradius reliably at the correct time

Measuring PISAMeasuring PISA

PISA is Proximal Isovelocity Surface Area PISA is Proximal Isovelocity Surface Area

It is larger in large volume jets and smaller It is larger in large volume jets and smaller in small volume jetsin small volume jets

It also will change its size depending on It also will change its size depending on the color Doppler scale factorthe color Doppler scale factor

PISA is just one of many ways to calculate PISA is just one of many ways to calculate severity of MR severity of MR

There are four hallmarks of flow in mitral four hallmarks of flow in mitral regurgitation: regurgitation: Flow convergenceFlow convergence that then narrows into an that then narrows into an

area of area of accelarated flowaccelarated flow (narrowest area of (narrowest area of flow) and then expands into the area of flow) and then expands into the area of turbulence (what we currently call the turbulence (what we currently call the size of size of the jetthe jet))

We also can see the downstream effects like We also can see the downstream effects like pulmonary vein flow reversalpulmonary vein flow reversal in systole in systole

So the hallmark flow areas on a diagram of So the hallmark flow areas on a diagram of mitral regurgitation mitral regurgitation

The PISA can be seen on this TEE MR jetThe PISA can be seen on this TEE MR jet

And the vena contracta can be seen on And the vena contracta can be seen on this same jetthis same jet

The area of flow convergence is where we The area of flow convergence is where we look for PISAlook for PISA

There are many concentric flow velocity There are many concentric flow velocity shells as flow accelerates into the vena shells as flow accelerates into the vena contractacontracta

Calculation of PISA requires us to find one Calculation of PISA requires us to find one of these shells and then calculate its of these shells and then calculate its surface areasurface area

This takes a lot of faith and skillThis takes a lot of faith and skill

It is almost always done from an apical It is almost always done from an apical view view

One thing to remember is that PISA (as One thing to remember is that PISA (as well as the other hallmark areas) will be well as the other hallmark areas) will be larger in large degrees of mitral larger in large degrees of mitral regurgitation regurgitation

Every MR jet has a flow convergence area Every MR jet has a flow convergence area and, therefore, a PISA of the jet and, therefore, a PISA of the jet

PISA looks at the flow convergence PISA looks at the flow convergence

Keep in mind, flow is always the area x the Keep in mind, flow is always the area x the velocityvelocity

We already know this from the continuity We already know this from the continuity equation and in Doppler calculations of equation and in Doppler calculations of cardiac output cardiac output

But we can’t clearly see the orifice, so for But we can’t clearly see the orifice, so for PISA we will look prior to the orificePISA we will look prior to the orifice

We will look at one of the isovelocity shells We will look at one of the isovelocity shells

Here area of the shell x velocity of the Here area of the shell x velocity of the shell equals flowshell equals flow

By the continuity equation, this flow By the continuity equation, this flow should be exactly that of the flow at the should be exactly that of the flow at the regurgitant orificeregurgitant orifice

So find a velocity shell and move the scale So find a velocity shell and move the scale factor to help you identify itfactor to help you identify it

Meaning of scale factorMeaning of scale factor

The use of the scale factor just helps us The use of the scale factor just helps us identify a suitable isovelocity shell for identify a suitable isovelocity shell for measurementmeasurement

Then we can use it to calculate flow Then we can use it to calculate flow

Note the PISA get larger in this MR jet. The Note the PISA get larger in this MR jet. The jet at the right is the same as on the left, jet at the right is the same as on the left, the only thing changed is the scale factorthe only thing changed is the scale factor

Here is a larger depiction of the previous Here is a larger depiction of the previous jetsjets

Moving the scale factor down will make Moving the scale factor down will make the shell bigger and easier to identify. the shell bigger and easier to identify.

So, now we have the shell and can read So, now we have the shell and can read the velocitythe velocity

Since we have the shell, measuring the Since we have the shell, measuring the radius will allow you to calculate the area radius will allow you to calculate the area of the shell or PISAof the shell or PISA

If we multiply the area x velocity we will If we multiply the area x velocity we will get the flowget the flow

So rememberSo remember

LimitationsLimitations

The biggest limitation of PISA is the The biggest limitation of PISA is the incorrect identification of the proximal flow incorrect identification of the proximal flow convergence areaconvergence area

Here is an example of an area where the Here is an example of an area where the flow convergence is not symmetric flow convergence is not symmetric

This is an example of a perforated mitral This is an example of a perforated mitral leaflet from the TEE approach (left)leaflet from the TEE approach (left)

Note the asymmetric flow convergence Note the asymmetric flow convergence areaarea

This is a limitation of PISAThis is a limitation of PISA

So we worry about non-optimal flow So we worry about non-optimal flow convergence and changes in the PISA over convergence and changes in the PISA over time (the cardiac cycle)time (the cardiac cycle)

Note the changes in size over the cardiac Note the changes in size over the cardiac cycle cycle

So PISA has limitationsSo PISA has limitations

Different textbooks have given the ranges Different textbooks have given the ranges of values but keep in mind, big is big and of values but keep in mind, big is big and small is small small is small

Thank YouThank You