Andersons pediatric cardiology 1066
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echocardiographicinvestigation,mostsuchneonateswillalreadybereceiving
prostaglandinsintravenously.Consequently,thearterialductwillberelatively
large.Althoughthepresenceofapatentarterialductwouldleadonetosuspect
thepresenceofinterruptionoftheaorticarch,ductalpatencymayrarelybe
presentinassociationwithanormalarch.28Thehighleftparasternalsection
demonstratestheduct,andcolorflowwillusuallydemonstratetheflowthrough
ittobebidirectional.PulsedDopplerinterrogationrevealsthatsystolicflowis
fromthepulmonaryarteriestothedescendingaorta,albeitthat,providedthatthe
pulmonaryvascularresistanceislow,therewillbereversalofflowduring
diastole.Thesuprasternalparasagittalsectionswillrevealthesiteofaortic
interruption,ifpresent,relativetotheoriginofthebrachiocephalic,leftcommon
carotidandleftsubclavianarteries.
CardiacMagneticResonanceand
ComputerizedTomographicImaging
Thesemodalitiesarerarelyusedintheinitialinvestigationofpatientswith
commonarterialtrunkbeforesurgerybecause,inmostinstances,
echocardiographyprovidesadequatediagnosticinformation.Nonetheless,there
maybesomeinstances,forexampleintheexaminationofcomplexproblemsof
theaorticarchoranomaliesofthedrainageofthepulmonaryveins,wherethey
maymakeacontributiontothepreoperativeinvestigation.Magneticresonance
imagingmakesamoresignificantcontributiontotheinvestigationsofpatients
aftersurgery,whenitpermitsthequantitativeassessmentofnotonlythe
performanceoftherightandleftventricles,butalsooftheseverityof
regurgitationoftheneoaorticandpulmonaryvalves,alongwithmeasurementof
residualintracardiacshuntsandimagingoftheaorticarch.29,30
CardiacCatheterizationand
Angiocardiography
Itisnowpossibletoreferpatientswithtypicalnoninvasivefindingsdirectlyfor
correctivesurgery.However,shouldtherebeanydoubtaboutanyaspectofthe
presentation,cardiaccatheterizationshouldbeconsidered,particularlyifthereis
anysuggestionofpulmonaryvascularobstructivedisease.31,32Thesystemic
consumptionofoxygenshouldbemeasuredwhilesamplesareobtainedfromthe
superiorcaval,theinferiorcavalvein,andthepulmonaryveins,aswellasfrom
thepulmonaryandsystemicarteriesformeasurementoftheiroxygencontent.
Theeffectofadministrationof100%oxygen,orpulmonaryvasodilators,should
bemeasured.Entrytothepulmonaryarteriesisachievedmostreadilyby
retrogradearterialcatheterization,loopingthecatheterinthetruncalrootsothat
itcanpassupwardsintothepulmonaryarteries.Oximetrywillrevealanincrease
inthesaturationofoxygeninthepulmonaryarteries,comparedwiththecaval
veins,indicativeofanetleft-to-rightshunt(Fig.40.19).Commonly,the
saturationofoxygeninthepulmonaryarteriesmaybelowerthanintheaorta,
reflectingthestreamingofbloodpreferentiallyfromtherightventricleto
pulmonaryarteries,andfromtheleftventricletotheaorta.Pulmonaryvenous
saturationsofoxygencannotbeassumedbecausepulmonaryedemaorchest
infectioncanresultinpulmonaryvenousdesaturation.
