Andersons pediatric cardiology 1760
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topreoperativehemodynamics.Morestudieswillneedtofocusonwhich
pediatricpatientsarebestservedwithBiVADsupport.
CongenitalHeartDisease
Long-termmechanicalsupportofCHDpresentsuniqueclinicalchallengesand
isassociatedwithsignificantlyworseoutcomesthanforcardiomyopathy
patients.32,49,50Thereasonsforthisislikelymultifactorial.Asidefromanatomic
andphysiologicvariations,manyofthesepatientsarenotplacedonsupportuntil
afteroneormorefailedoperationsandfrequentlyintheimmediate
postcardiotomyperiod.Manyofthesepatientsalsohaveintracardiac
communications,mixedcirculations,orSVP,whichcanmaketheuseofVADs
quitedifficult.Inpatientswithtwo-ventriclephysiology,allintracardiacshunts
shouldbeclosedatthetimeofLVADimplantationtoavoiddesaturation.In
patientswithsystemic-to-pulmonaryshunts,itisnowbelievedbesttoleavethe
shuntopenandruntheVADathigherflowrates.Thishasnotbeenstudied,yet
itisthegeneralfeelingamongmostpediatricVADprograms.
SmallstudiespriortotheNorthAmericanBerlinHeartEXCORexperience
hadshownCHDtobeariskfactorformortalityinheartfailurepatientsonVAD
supportwhencomparedwithnon-CHDpatients.1,51Thesedataaresimilartothe
Europeanexperience,whichfoundonlya47%successfulbridgeforallCHD
patients.52InthecombinedEXCORstudy,59of204(29%)ofthepatientshad
CHD.53Thesepatientsweremorelikelytobemechanicallyventilated,havehad
priorcardiacsurgery,andhavesevererenalandhepaticdysfunction,which
emphasizestheimportanceofend-organfunctioninpatientselection.CHD
patientswereconsiderablylesslikelytosuccessfullybridgetotransplantor
weanfromVAD(80%vs.48%)versusnon-CHDpatients.IfECMOpriorto
VADwasassociatedwithcongenitalheartsurgery,“salvageVAD”survivalwas
17%comparedwith82%inpatientsrequiringECMOwithoutpriorcardiac
surgeryinthesameadmission.Itisimportanttorecognizethatagealsoplayed
animportantroleinsurvival,with92%ofneonatesandinfantsdying,although
thevastmajorityofthesepatientsweresalvageVADscomparedwith60%ofthe
childrenolderthan1year.ThisledtheauthorstoconcludethatEXCORsupport
maynotprovideanysurvivalbenefitinneonatesandinfantswithpreimplant
congenitalheartsurgeryandECMObutthatchildrenolderthan1yearwith
CHDcanbesuccessfullyandconsistentlysupportedwiththeEXCOR.Again,
theissueispatientselectionandtimingofimplant.Ithasbeendocumented
repeatedlythatafailedpalliationtoECMOthentoaVAD,especiallyinan
infant,willveryrarelybesuccessful.Nonetheless,thissequencecomprisesmost
ofthecongenitaldataininfants.However,onecanexpectreasonablesurvivalto
transplantinapatientwithCHDwhoisINTERMACS2orhigherwhois
supportedpriortoend-organdysfunction.Inaddition,despitebeingmoreill
(increasedcreatinine,hepaticdysfunction,moremechanicalventilation,etc.),
congenitalpatientsbridgedtotransplantwithVADsupporthadsimilar
posttransplantoutcomestocongenitalpatientsnotbridgedwithVADsupport.
ThereforeVADsupportseemedtomitigatesomeoftheusualriskfactorsfor
poortransplantoutcomes.
SingleVentricleHearts
Beforeenteringintodiscussionaboutdeviceoutcomesinpatientswithsingle
ventriclehearts(SVHs),itmustbenotedthatweusethetermSVPtodescribea
patientwith(1)completeintracardiacmixingofthesystemicandpulmonary
venousreturns;and(2)distributionoftheCObetweentwoparallelcompeting
circuits(e.g.,hypoplasticleftheartsyndrome,unrepairedaortopulmonary
window,shuntedpatients).Whenpossible,patientshavingundergonestageII
(Glenn)orstageIII(Fontan)repairarereferredtoseparately.SVHrefersto
patientsinthesingleventriclepathwayatanystageduetohistoricalgroupings
inpriorstudiesandsimplicityfordiscussion;also,bythetimethesepatients
presentinheartfailure,theyusuallyhavesignificantaortopulmonarycollaterals
(systemictopulmonaryshunting).
ThelargeststudiesofVADsinSVHpatientscomefrom26patientsinthe
NorthAmericanEXCORstudy54andanother7patientsinaseriesbyDeRitaet
al.55AllpatientsreceivedEXCORdevices,withbothstudieshavingasurvival
totransplantof42%.Thiswassignificantlylowerthanthe73%survivalto
transplantseeninthebiventricularpopulation.Weinsteinetal.foundthat
survivalvariedbystage.EightoutofninepatientsreceivingEXCORafterstage
Ipalliationdied,theonlysurvivorbeinganoninfantwhounderwentDamusKaye-StanselprocedureandmodifiedBlalock-Taussigshuntat19monthsof
age.Asofyet,noonehasreportedthesuccessfulsupportofaneonateaftera
NorwoodoperationtotransplantandhomeusinganEXCORVAD.Incontrast,7
of12patientsVADsupportedafterstageIIand3of5patientsVADsupported
afterFontanoperationsurvivedtotransplant.Thereforesurvivaltotransplant
comparedfavorablytoECMOinthispopulation,andimportantly,survivalafter
transplantwasnotdifferentfrompatientstransplantedwithoutMCS.Patients
afterGlennpalliationtendtodowellbecausetheyaregenerallypatientswhose
circulationisfailingovertimeasopposedtobeingplacedonaVADasasalvage
procedure,immediatelyaftersurgery.Manytimes,Glennpalliatedpatientshave
beendischargedhomebutdevelopend-stageheartfailurepriortoFontan.There
arealwaysthosepatientsinwhomwehopetheirventricularfunctionwill
improveafterGlennandvolumeunloading,butunfortunately,someneverdo.In
rareinstances,theEXCORcanbesetupinaBiVADfashioninSVH.54,56,57A
recentreportdescribesanovelfour-stagetransitionfromurgentperipheral
ECMOtocentrifugalVADtoEXCORinafailingFontanconnection.58This
processallowedthelungstohealfollowingtheinitialcentralcannulationwith
centrifugalpumpbymaintainingperipheralECMOcannulationpriorto
switchingtofullcentralsupport.Subsequently,thefenestrationwasclosedand
theoxygenatorremovedbeforeconvertingtofullEXCORsupport.Mostexperts
believethattheFontancirculationisnotwellsupportedbyperipheralECMO,
andmostrecommendthatafterinitialstabilizationwithECPR,central
cannulationwithcommonatrialdecompressionisanimportantsteptoward
successfuldurableVADsupport.
FailuresofECMOinGlennphysiologyhavebeenattributedtochallenges
withcannulation,highcentralvenouspressuresleadingtoneurologicinjury,and
itscommonuseaftercardiacarrest.AlthoughGlennphysiologytypically
representsa“volume-unloaded”circulationcomparedwithSVP,patientsinheart
failureoftenpresentwithsignificantcollateralcirculationleadingtoahigher
thanexpectedCOdemandthanwhatwouldbeanticipatedfortheirBSA.
Conversely,boththeEXCOR32,59andcentrifugal60–62VADshavebeenused
successfullyinGlennphysiology.Thisisinpartbecausethesepatientstendto
notbesalvageVADs,ratherasystemicventriclethathasfailedovertime.
Overthepastfewyears,VADsupportforsingleventriclepatients(shunted,
banded,orwithsignificantcollateralflow[e.g.,failingGlenn])hasprogressed
andthereisnowanappreciationthatthepreloadofsuchpatientsisquite
variable,especiallyduringtheperioperativeperiod.Assuch,supportwiththe
EXCOR,whoseresponsetopreloadisnotdynamicandrequiresmanual
manipulationofitsparametersunlikecentrifugalpumps,isnotideal.Thereforea
practicegainingwidespreadapplicationistheuseofEXCORcannulasin
combinationwithacentrifugalpumpasaforementioned(e.g.,Pedi/CentriMag,
ROTAFLOW).AcentrifugalVAD'soutputvarieswiththesystemicresistance
encountered,andtheyareabletoself-adjusttopreloaddemandssecondaryto
