Andersons pediatric cardiology 985
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pulmonaryvascularresistanceinpatientsforwhomthereisaclinicalsuspicion
ofpulmonaryvasculardisease,orforadditionalanatomicorphysiologic
information.
MagneticResonanceImaging
Althoughtransthoracicechocardiographyistypicallysufficient,preoperative
magneticresonanceimagingmayprovideusefulcomplementaryinformationin
theassessmentoftheanatomy.Itisparticularlyusefulintheassessmentofthe
massoftheleftventricleintheinfantpresentinglate(Fig.37.14).Thismay
assistcliniciansinassessingthesuitabilityofanindividualpatientforanarterial
switchoperation.Inanovelapplication,four-dimensionalsequenceshavebeen
usedtoassessstreamingofflowinbothrepairedandunrepairedpatients.38,39
Furtherdiscussionofpostoperativeuseofmagneticresonanceimagingfollows
inthischapter.
FIG.37.14 Magneticresonanceangiogramina9-month-oldpatientwho
presentedfromadevelopingcountrywithanintactventricularseptum.The
aorta(Ao)canbeenseenarisingfromtherightventricle(RV)andthe
pulmonarytrunk(PT)fromtheleftventricle(LV).
MedicalManagementofNeonates
PostnatalStabilisation
Carefulandtimelymanagementoftheneonatewithtranspositioniscriticalto
minimizepreoperativemortality,whichrangesfrom3%to10%.40–42Optimal
managementrequiresthoughtfulconsiderationoftherisksandbenefitsrelatedto
atrialseptostomy,mechanicalventilation,theuseofprostaglandin,andthe
timingofsurgery.43
Neonatesdiagnosedinuteroshouldbedelivered,preferablyatterm,inahighriskobstetricunit,withrapidaccesstoadvancedcardiaccare,includingthe
availabilityofatrialseptostomy.43Amongmanyotherbenefits,termdelivery
allowsformorecompletematurationofthebraininthispatientpopulationin
whomitisknownthatoxygendeliverytothefetalbrainissignificantly
diminishedcomparedwithnormal.Venousaccessshouldbeobtained
immediatelyafterdelivery,andaninfusionofprostaglandinEshouldbeatleast
readied,ifnotstartedempirically.Thecommonsideeffectsofprostaglandin
shouldbeanticipated,includingapnea,hypotension,andfever.Lowerstarting
doses(0.0125µg/kgperminuteatourinstitution)areusuallyadequate.
Prompttransthoracicechocardiographywilldefinethenatureoftheanatomy
andguidetherapy.Patientswithsevereacidosisorhypoxemia,usually
attributabletoinadequatemixingattheatriallevel,mayrequireanurgent
balloonatrialseptostomy.Thisisthecaseinupto12%ofneonates.41Inothers,
anonurgentseptostomyisperformediftherearesignsofinadequateintracardiac
mixing,includingacidosis,decreasedsystemicperfusion,orhypoxemia,orif
echocardiographicfindingssuggestariskforinadequatemixing.Asdiscussed
later,thethresholdforperforminganelectiveseptostomyisinstitution
dependent.Aspreviouslymentioned,onemustnotbemisledbythelackofa
demonstrablepressuregradientfromleft-to-rightatriumontheechocardiogram,
and,ifotherindicatorsofinadequatemixingarepresent,aseptostomyshouldbe
considered.Althoughtraditionalteachinghasadvisedagainsttheuseof
supplementaloxygen,modestamountsmaybebeneficialduringtheearly
postnatalhoursbycompensatingforanyalveoloarterialgradientandreducing
pulmonaryvascularresistance.
AtrialSeptostomy
FollowingitsintroductionbyRashkindandMillerin1966,44theballoonatrial
septostomyhasbecomewellacceptedinthepreoperativemanagementof
patientswithtranspositionandselectedotherlesions.Theprocedurerequires
passageofaballoon-tippedcatheterfromtheright-to-leftatrium,crossingthe
ovalforamen.Theballoonistheninflatedwithsalineand,withaquick,short
motion,ispulledintotherightatrium.Althoughafemoralvenousapproachwas
originallydescribed,itisnowcommontousetheumbilicalveintoenterthe
heartthroughthevenousduct.Fluoroscopicscreeningwaspreviouslyusedto
guidetheprocedure(Fig.37.15)buthaslargelybeenreplacedbycross-sectional
echocardiography(Fig.37.16,Video37.3).Thisprovidesasimpleandreliable
methodformonitoringthepositionoftheballoonandassessingthesuccessof
theseptostomy.Italsoallowstheproceduretobeperformedoutsideofthe
cardiaccatheterizationsuite.
FIG.37.15 Fluoroscopicimagesfromapatientundergoinganatrial
septostomy.Althoughtheballoonisclearlyvisible,itspreciserelationships
withimportantstructures,includingthemitralvalveandthepulmonary
veins,aredifficulttodiscern.
