Andersons pediatric cardiology 983
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ClinicalDiagnosis
Presentation
Theincreasingfrequencyofantenataldiagnosisoftranspositionallowsthe
clinicalteamtodelivertheinfantinaspecialistcenterorarrangeprompttransfer
forthosebornoutsideofsuchcenters.23Asaresult,time-sensitiveand
potentiallylifesavinginterventionssuchastheinitiationofaprostaglandin
infusionandballoonatrialseptostomycanbeexpeditedandthepotentialfor
hemodynamicinstabilityreduced.24
Mostnewbornswithtranspositionhaveanormalbirthweight.25Theyhave
beennotedtohavesmalleroccipitofrontalcircumferencesatbirththancontrols,
whichmayreflecttheabnormalhemodynamicsinutero,withrelatively
desaturatedbloodcirculatingtothebrainandupperbody.26,27Undiagnosed
infantscanpresentwithcyanosis,withorwithoutclinicalevidenceof
circulatoryinsufficiency.Asdiscussed,QEPandQESdependontheextentof
circulatorymixing.Intheextreme,someinfantsmaypresentshortlyafterbirth
withcyanosisandcirculatorycollapse,whichismostoftenrelatedtoinadequacy
oftheinteratrialcommunication.Infantswithawidelypatentarterialductanda
largeunrestrictiveventricularseptaldefectmaypresentwithonlyminimal
cyanosisand,instead,laterdevelopsignsofpulmonaryovercirculation.
Clinicalexaminationduringinfancyrevealsavariabledegreeofcyanosis,
whichisincompletelyresponsivetosupplementaloxygen.Theadequacyofthe
peripheralpulsesgenerallyreflectstheoverallcirculatorystate.Infantswithreal
orpendingcirculatorycollapsewilltendtobeprofoundlydesaturated,with
globallyreducedperipheralperfusion,coolextremities,andweakpulses.
Decreasedpulsesnotedonlyinthelowerextremitiesshouldalerttheclinicianto
anassociatedcoarctationorinterruptionoftheaorta.Anuppertolower
extremitybloodpressuregradientmaybepresent.Cardiacauscultationtypically
revealsasinglesecondheartsoundattributabletotherelativepositionsofthe
aorticandpulmonaryvalves.Theremaybeanaudiblecontinuousmurmurfrom
thearterialductorasystolicmurmurrelatedtoaventricularseptaldefect.Large
septaldefectswilleventuallyresultinfindingsconsistentwithpulmonary
overcirculationincludingtachypnea,dyspnea,hepatomegaly,feedingdifficulty,
andfailuretothrive.
ChestRadiography
Thechestradiographmayormaynotbeabnormal.Cardiacsizeisoftennormal,
whereasthepulmonaryvascularmarkingsmaybereduced,normal,orincreased,
reflectingthevolumeofflowtothelungs.Inapproximatelyone-thirdof
neonates,themediastinumisnarrow,aresultoftheanteroposteriorrelationship
ofthearterialtrunks.Thisclassicfindinghasbeendescribedasresemblingan
“eggonastring.”
Electrocardiography
Inmostnewborns,theelectrocardiogramisnormal.Duringearlyinfancypriorto
surgicalintervention,theelectrocardiogrammaybegintoreflectrightventricular
hypertrophyandlaterdemonstrateright-axisdeviation.Asuperioraxisinthe
neonatalperiodsuggestsassociatedabnormalitiesofthetricuspidvalve,
particularlystraddlingoroverriding.
FetalImaging
Inthemodernera,transpositionisbeingdiagnosedmorefrequentlyinuterothan
ithasinthepast;however,evenrecentseriesdemonstratethatlessthanhalfof
patientshaveanantenataldiagnosis.23,28Theefficacyoffetalscreeningisbased
onthepremisethatearlydetectionwillprovideopportunitiesforparentalchoice
andallowoptimalneonatalcareandpreoperativemanagement.Insomeseries,
reductionsinbothpreoperativeandpostoperativemorbidity,aswellasmortality,
havebeendemonstratedinneonatesafteranantenataldiagnosisof
transposition.24,28However,thedataaremixed,withotherstudiesreportingno
suchbenefit.29,30
Inmothersreferredforcomprehensivefetalechocardiographyperformedby
specialistsonographers,thelesioncanbedetectedwithhighlevelsofaccuracy
(Fig.37.10,Video37.1).30Asystematicsegmentalapproachisrecommended.31
Adetailedassessmentoftheadequacyofintracardiacmixing,particularlyatthe
atriallevel,isusuallyperformed.Restrictiontoflowattheatriallevelisahighly
specificpredictoroftheneedforemergencyneonatalcare,butitssensitivityis
toolowtopermitdetectioninallfetuses.32Findingsofasmallovalforamen
relativetothetotalseptallengthandreversalofflowthroughthearterialduct
duringdiastolehavebeenassociatedwiththeneedforanearlyatrial
septostomy.33,34Therearemixeddataregardingwhetherincreasedmobilityof
theflapoftheseptumprimumissimilarlypredictive.Four-dimensionalfetal
echocardiographymayprovideanadvantageovercross-sectionalimaginginthat
itcreatesanenfaceviewofthefourcardiacvalves,thusenhancingthe
definitionofthespatialrelationshipsofthegreatarteriesand,inturn,improving
theprobabilityofpredictinganabnormaldistributionofthecoronaryarteries.35
Cardiacmagneticresonancemaybeusedtodetectreductionsinflowattheatrial
andductallevelsandexcessiveflowthroughaortopulmonarycollateral
arteries.36
FIG.37.10 Fetalechocardiogramdemonstratingtheaorta(Ao)arising
fromtherightventricle(RV)andthepulmonaryarteryfromtheleftventricle
(LV).Notetheparallelorientationofthegreatvessels,notseeninnormally
connectedhearts.LPA,Leftpulmonaryartery;RPA,rightpulmonaryartery.
PostnatalEchocardiography
Theechocardiographicexaminationoftheneonatewithtranspositionrequiresa
completeassessmentoftheanatomy,usingasequentialapproach,an
examinationofthecirculatoryphysiology,particularlyoftheadequacyof
mixing,andanestimationoftheabilityoftheleftventricletosupportthe
systemiccirculation.Echocardiographicconfirmationofthediagnosisrequires
