Andersons pediatric cardiology 1867
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FutureConsiderations
EventhesuccessfulFontansurvivorfacesanumberoflong-termchallenges,
includingheartfailure,thromboemboliccomplications,arrhythmias,residual
cyanosis,chronicvenousinsufficiency,liverdisease,renaldisease,and
abnormalitiesoflymphaticdrainageincludingprotein-losingenteropathyand
plasticbronchitis.
Thethoracicductdrainsintothecentralvenoussysteminthechest,andthe
elevationofcentralvenouspressurethatoccurswiththeFontanwillaffect
normallymphaticdrainage.Advancesinimagingofthelymphaticsystemhave
identifiedabnormalflowpatterns,includingretrogradeflowinthethoracicduct
andabnormalconnectionswiththegutandlungs;thesecontributetoproteinlosingenteropathyandplasticbronchitis.320Interventionalstrategiesincluding
lymphaticembolizationhaveresultedinimprovementinindividualcases.321,322
Surgicalthoracicductdecompression,achievedbyanastomosisofthe
innominateveintothepulmonaryvenousatrium,hasalsobeenperformedfor
protein-losingenteropathyandchylousascites.323Modificationofthelymphatic
systembyinterventionalorsurgicalmeanswilllikelyincreaseasourabilityto
imageandunderstandthelymphaticsystem'spathophysiologyincreases.
Hearttransplantationmaybetheonlyoptionforpatientswithend-stageheart
diseasefollowingtheFontan.Theymayhavecongenitalheartdiseasethat
includesabnormalitiesofcardiacpositionandvenousanatomy.Theyhavehad
multiplepreviouscardiacproceduresandasaconsequencemaybesensitized;
theywillhavemultiplecollateralvesselsandvenoushypertension,allofwhich
increasetheriskofthetransplantprocedure.324,325Inaddition,theseFontan
survivorsfrequentlyhaverenalandhepaticdysfunction,whichcomplicatestheir
posttransplantcourse.326,327ThepulmonaryvasculatureofthesurvivingFontan
patientisabnormalduetoalteredflowdistributionaswellasthepresenceof
aortopulmonarycollateralsandpulmonaryAVMs.328Whereasitwasonce
assumedthattheFontansurvivorhadlowPVRs,thePVRmayinfactbe
elevated,andthismaybeunmaskedintheposttransplantpatient.Despitethese
challenges,recentexperiencedemonstratesimprovedoutcomeswithheart
transplantationinthispopulation,witha5-yearposttransplantsurvivalofgreater
than70%.329–331
Mechanicalcirculatorysupportwilllikelyplayagreaterroleinthe
managementofthefailingFontanpatientduetothechallengesofmedical
therapy,scarcityoforgandonors,andimprovedoutcomesofmechanical
circulatorysupportinthenoncongenitalpopulation.332–334Short-termtemporary
extracorporealdevicessuchastheCentrimagorRotaflowcanbecombinedwith
typicalbypasscannulasorBerlinHeartcannulastoprovidetemporarysupport
asbridgetotransplant.Newercontinuous-flowdevicessuchastheHeartWareor
HeartMate3aresmallerandmoreadaptabletoatypicalanatomyandhavebeen
adaptedforuseinthefUVHpopulation.335,336Therehasbeensomeexperience
usingtheTotalArtificialHeartinthefailingFontanpatient.337Finally,devices
designedtoreplacerightventricularfunctionwhilepreservingtheFontan
pathwayareindevelopment.338Theentirefieldofmechanicalcirculatory
supportisrapidlyadvancing.Althoughsuchsupportiscurrentlyusedonlyasa
bridgetotransplantordecision,mechanicalcirculatorysupportwillplayarole
asdurabletherapyforthefailingFontanpatientinthenearfuture.
Theroleofstem-celltherapytotreatventriculardysfunctionisbeingexplored
byseveralgroups.Aphase2studyusingintracoronaryinjectionofautologous
cardiosphere-derivedcellsatthetimeoftheSCPCortheFontanprocedurehas
shownamodestbutsignificantimprovementinsingle-right-ventricleejection
fractionasmeasuredbyMRI.339Othergroupsareinvestigatingumbilicalcord–
derivedautologouscellsinindividualswithaprenataldiagnosisoffUVH.340
Finally,allogenicmesenchymalstemcellsarebeinginvestigated.341Theextent
anddurationofbenefit,idealcelltype,routeofadministration,andintracoronary
versusdirectmyocardialinjectionremaintobedetermined.Neverthelessthe
resultsareintriguing,andcell-basedtherapymaybecomearoutinestrategyto
improvelong-termfunctioninpatientswithfUVH.
ClosingThoughts
Thepinnacleofvertebrateevolutionisthedevelopmentofthetwoventricle
circulationwithdedicatedpulmonaryandsystemicpumpingchambersresulting
infullysaturatedhemoglobinthatsupportsthehighmetabolicratecharacteristic
ofbirdsandmammals.Despitewhatwouldseemlikeaninsurmountable
limitationofthecirculatorysystem,wehavewitnessedoverashort,75-year
spanthedevelopmentofstrategiestocareforthepatientwithfUVHthat
restoresin-seriescirculationandpermitslong-termsurvival.Theprogressinthe
careoftheseindividualshasimpactedthecareofeverypatientwithcongenital
heartdisease;muchofourmanagementstrategies,especiallyintheareaof
criticalcare,areaconsequenceofthelessonslearnedfromthesemost
challengingpatients.FortheindividualwithfUVHthefundamentalproblemof
animpairedcirculationpersiststhroughoutlife.Despitetheselimitations,
survivorsofpalliationoffUVHaregrowingup,havingfamiliesoftheirown,
andinspiringuswiththeircourageandtenacity.Ongoingresearchprovideshope
forthefutureandwillbefocusedonidentifyingthecausesofcardiac
maldevelopment,diagnosingearlier,improvingfetalintervention,improving
medicaltherapy,optimizingtransplantoutcomes,expandingtheuseof
mechanicalcirculatorysupport,andimprovingfunctionaloutcomes,qualityof
life,andneurodevelopmentaloutcomes.
