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- 1. PProximalroximalIIsovelocitysovelocitySSurfaceurfaceAAreareaDr. Sehran BhattiDr. Sehran Bhatti
- 2. Regurgitant volumes can be estimated by 2Regurgitant volumes can be estimated by 2methodsmethods 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
- 3. If regurgitant orifice area is known thenIf regurgitant orifice area is known thenreguritant volume can be estimated as thereguritant volume can be estimated as theproduct of effective regurgitant orifice areaproduct of effective regurgitant orifice area(ERO) and regurgitant TVI(ERO) and regurgitant TVI To estimate ERO, Proximal isovelocity surfaceTo estimate ERO, Proximal isovelocity surfacearea is usedarea is usedRV = ERO x Regurgitant TVIRV = ERO x Regurgitant TVI
- 4. As blood flow converges towards the regurgitantAs blood flow converges towards the regurgitantorifice, blood flow velocity increases withorifice, blood flow velocity increases withformation of multiple shells of isovelocity offormation of multiple shells of isovelocity ofhemispheric shapehemispheric shape Remember that velocity of the shell closest toRemember that velocity of the shell closest tothe regurgitant orifice is highest and vice versathe regurgitant orifice is highest and vice versa The flow rate at the surface of a hemisphericThe flow rate at the surface of a hemisphericshell with the same flow velocity is consideredshell with the same flow velocity is consideredequal to the flow rate across the regurgitantequal to the flow rate across the regurgitantorifice according to the law of conservation oforifice according to the law of conservation offlow which states thatflow which states that““What comes in must go out”What comes in must go out”
- 5. By adjusting the Nyquist limit of the color flow map, theBy adjusting the Nyquist limit of the color flow map, theflow velocity of a hemispheric surface proximal to theflow velocity of a hemispheric surface proximal to theregurgitant orifice can be determinedregurgitant orifice can be determined For e.g. in MR the regurgitant flow travels away from theFor e.g. in MR the regurgitant flow travels away from theposition of the apical transducer ans so the bloodposition of the apical transducer ans so the bloodconverging towards the mitral regurgitant orifice in theconverging towards the mitral regurgitant orifice in theLV is color coded blue until the velocity reaches theLV is color coded blue until the velocity reaches thenegative aliasing velocity of the selected color flow map,negative aliasing velocity of the selected color flow map,at which time the flow will change color to light orange-at which time the flow will change color to light orange-redred If the negative aliasing velocity of the color map isIf the negative aliasing velocity of the color map isreduced further, the trasition from blue to orange-red willreduced further, the trasition from blue to orange-red willoccur farther from the regurgitant orifice providing aoccur farther from the regurgitant orifice providing alarger hemispheric shell radiuslarger hemispheric shell radius
- 6. After a hemisphere with blood flow of isovelocityAfter a hemisphere with blood flow of isovelocityis identified the flow rate through thisis identified the flow rate through thishemispheric shell is determined byhemispheric shell is determined byFlow rate = CSA x VelocityFlow rate = CSA x VelocityArea of hemispheric shell = 2Area of hemispheric shell = 2ππr², where pie=3.14r², where pie=3.14Flow rate = 6.28 x r² x Aliasing velocity (from color map)Flow rate = 6.28 x r² x Aliasing velocity (from color map)
- 7. As we have already discussed the flow rate atAs we have already discussed the flow rate atthe surface of a hemispheric shell with the samethe surface of a hemispheric shell with the sameflow velocity is considered equal to the flow rateflow velocity is considered equal to the flow rateacross the regurgitant orifice according to theacross the regurgitant orifice according to thelaw of conservation of flowlaw of conservation of flow Therefore, this flow across PISA is equal to flowTherefore, this flow across PISA is equal to flowrate across EROrate across EROFlow rate = ERO x regurgitant velocityFlow rate = ERO x regurgitant velocityERO = flow rate / peak MR velocityERO = flow rate / peak MR velocityERO = 6.28 x r² x Aliasing velocity / MR velocityERO = 6.28 x r² x Aliasing velocity / MR velocity
- 8. Regurgitant Volume = ERO x MR TVIRegurgitant Volume = ERO x MR TVISubstituting value of ERO we getSubstituting value of ERO we getRegurg Vol = 6.28 x r² xRegurg Vol = 6.28 x r² x Aliasing velocityAliasing velocity x MRTVIx MRTVIMR velocityMR velocity
- 9. The concept of PISA can also be applied toThe concept of PISA can also be applied tocalculate the area of stenotic surfaces and hascalculate the area of stenotic surfaces and hasbeen validated for MV area in patients with mitralbeen validated for MV area in patients with mitralstenosisstenosis
- 10. CaveatsCaveats Proximal to a stenotic mitral orifice, PISA mayProximal to a stenotic mitral orifice, PISA maynot be a complete hemisphere but a portion ofnot be a complete hemisphere but a portion ofhemisphere because of mitral leaflets geometryhemisphere because of mitral leaflets geometryon the atrial sideon the atrial side In such cases an angle correction factor isIn such cases an angle correction factor isappliedappliedMVA = 6.28 x r² xMVA = 6.28 x r² x Aliasing velocityAliasing velocity xx 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
- 11. Sometimes it is difficult to know in which direction theSometimes it is difficult to know in which direction thebaseline should be shifted for optimal PISAbaseline should be shifted for optimal PISA For this rule of the thumb is to shift the baseline inFor this rule of the thumb is to shift the baseline inthe direction of the flow jet of interestthe direction of the flow jet of interest PISA radius needs to be measured at the same time asPISA radius needs to be measured at the same time asthe peak velocity of the jetthe peak velocity of the jet Color M-mode can help in measuring the radiusColor M-mode can help in measuring the radiusreliably at the correct timereliably at the correct time
- 12. Measuring PISAMeasuring PISA PISA is Proximal Isovelocity Surface AreaPISA is Proximal Isovelocity Surface Area It is larger in large volume jets and smaller inIt is larger in large volume jets and smaller insmall volume jetssmall volume jets It also will change its size depending on theIt also will change its size depending on thecolor Doppler scale factorcolor Doppler scale factor
- 13. PISA is just one of many ways to calculatePISA is just one of many ways to calculateseverity of MRseverity of MR
- 14. There are four hallmarks of flow in mitralfour hallmarks of flow in mitralregurgitation:regurgitation: Flow convergenceFlow convergence that then narrows into anthat then narrows into anarea ofarea of accelarated flowaccelarated flow (narrowest area of(narrowest area offlow) and then expands into the area offlow) and then expands into the area ofturbulence (what we currently call theturbulence (what we currently call the size ofsize ofthe jetthe jet)) We also can see the downstream effects likeWe also can see the downstream effects likepulmonary vein flow reversalpulmonary vein flow reversal in systolein systole
- 15. So the hallmark flow areas on a diagram ofSo the hallmark flow areas on a diagram ofmitral regurgitationmitral regurgitation
- 16. The PISA can be seen on this TEE MR jetThe PISA can be seen on this TEE MR jet
- 17. And the vena contracta can be seen on thisAnd the vena contracta can be seen on thissame jetsame jet
- 18. The area of flow convergence is where we lookThe area of flow convergence is where we lookfor PISAfor PISA There are many concentric flow velocity shellsThere are many concentric flow velocity shellsas flow accelerates into the vena contractaas flow accelerates into the vena contracta
- 19. Calculation of PISA requires us to find one ofCalculation of PISA requires us to find one ofthese shells and then calculate its surface areathese shells and then calculate its surface area This takes a lot of faith and skillThis takes a lot of faith and skill It is almost always done from an apical viewIt is almost always done from an apical view
- 20. One thing to remember is that PISA (as well asOne thing to remember is that PISA (as well asthe other hallmark areas) will be larger in largethe other hallmark areas) will be larger in largedegrees of mitral regurgitationdegrees of mitral regurgitation
- 21. Every MR jet has a flow convergence area and,Every MR jet has a flow convergence area and,therefore, a PISA of the jettherefore, a PISA of the jet
- 22. PISA looks at the flow convergencePISA looks at the flow convergence
- 23. Keep in mind, flow is always the area x theKeep in mind, flow is always the area x thevelocityvelocity We already know this from the continuityWe already know this from the continuityequation and in Doppler calculations of cardiacequation and in Doppler calculations of cardiacoutputoutput
- 24. But we can’t clearly see the orifice, so for PISABut we can’t clearly see the orifice, so for PISAwe will look prior to the orificewe will look prior to the orifice We will look at one of the isovelocity shellsWe will look at one of the isovelocity shells
- 25. Here area of the shell x velocity of the shellHere area of the shell x velocity of the shellequals flowequals flow By the continuity equation, this flow should beBy the continuity equation, this flow should beexactly that of the flow at the regurgitant orificeexactly that of the flow at the regurgitant orifice
- 26. So find a velocity shell and move the scale factorSo find a velocity shell and move the scale factorto help you identify itto help you identify it
- 27. Meaning of scale factorMeaning of scale factor The use of the scale factor just helps us identifyThe use of the scale factor just helps us identifya suitable isovelocity shell for measurementa suitable isovelocity shell for measurement Then we can use it to calculate flowThen we can use it to calculate flow
- 28. Note the PISA get larger in this MR jet. The jet atNote the PISA get larger in this MR jet. The jet atthe right is the same as on the left, the only thingthe right is the same as on the left, the only thingchanged is the scale factorchanged is the scale factor
- 29. Here is a larger depiction of the previous jetsHere is a larger depiction of the previous jets
- 30. Moving the scale factor down will make the shellMoving the scale factor down will make the shellbigger and easier to identify.bigger and easier to identify. So, now we have the shell and can read theSo, now we have the shell and can read thevelocityvelocity
- 31. Since we have the shell, measuring the radiusSince we have the shell, measuring the radiuswill allow you to calculate the area of the shell orwill allow you to calculate the area of the shell orPISAPISA
- 32. If we multiply the area x velocity we will get theIf we multiply the area x velocity we will get theflowflow
- 33. So rememberSo remember
- 34. LimitationsLimitations The biggest limitation of PISA is the incorrectThe biggest limitation of PISA is the incorrectidentification of the proximal flow convergenceidentification of the proximal flow convergenceareaarea
- 35. Here is an example of an area where the flowHere is an example of an area where the flowconvergence is not symmetricconvergence is not symmetric
- 36. This is an example of a perforated mitral leafletThis is an example of a perforated mitral leafletfrom the TEE approach (left)from the TEE approach (left) Note the asymmetric flow convergence areaNote the asymmetric flow convergence area This is a limitation of PISAThis is a limitation of PISA
- 37. So we worry about non-optimal flowSo we worry about non-optimal flowconvergence and changes in the PISA over timeconvergence and changes in the PISA over time(the cardiac cycle)(the cardiac cycle)
- 38. Note the changes in size over the cardiac cycleNote the changes in size over the cardiac cycle
- 39. So PISA has limitationsSo PISA has limitations Different textbooks have given the ranges ofDifferent textbooks have given the ranges ofvalues but keep in mind, big is big and small isvalues but keep in mind, big is big and small issmallsmall
- 40. Thank YouThank You

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