Andersons pediatric cardiology 976
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HistoricalBackground
Tothebestofourknowledge,itwasJohnFarre4whofirstusedtheterm
transpositioninthecontextofacardiacmalformation.Subsequenttothis
description,itwasusuallyconsideredthattheaortaneededtobeanteriorto
justifydiagnosis,combinedwithsupportoftheaorticvalvebyamuscular
infundibulum.However,somesegmentalcombinationsassociatedwithan
anterioraortaproducephysiologiccorrectionofthecirculatorypatterns,such
thatthesystemicvenousbloodreachesthelungsdespitebeingpumpedbythe
morphologicallyinappropriateventricle.Intwosuchcombinations,thereisalso
so-calledanatomiccorrection,inthattheaortatakesitsoriginfromthe
morphologicallyleftventricledespiteitsanteriorposition.Intwoadditional
variants,thecirculationsareinparallelratherthaninseries,despitethefactthat
theaortaarisesinconcordantfashionfromthemorphologicallyleftventricle.It
wasthisuseof“corrected”inananatomicsense,beingdependentonthe
definitionoftranspositionasananterioraorta,thatproducedthepotentialfor
confusion.5Furtherproblemsarosewhenitwasrecognizedthattheaortacould
ariseinappropriatelyfromthemorphologicallyrightventriclewheninposterior
positionandwithitsvalveinfibrouscontinuitywiththemitralvalve.6Itmakes
littlesense,whenconsideringclinicalpresentation,todescribeapatientwithan
anterioraortaarisingfromtheleftventricleashaving“transposition”whenthe
atrioventricularconnectionsarealsoconcordant,justasitmakeslittlesenseto
suggestthatpatientswithdiscordantventriculoarterialconnections,butwitha
posterioraorta,donothavetransposition.Thus,overrecentyears,therehasbeen
anincreasinggroundswellofopinioninfavorofdefiningtranspositiononthe
basisoftheoriginofthegreatarterialtrunksfrommorphologicallyinappropriate
ventricles.Therefore,thesystemthatwecurrentlyusebasestheuseof
“transposition”onthecombinationofspecificatrioventricularand
ventriculoarterialconnections.Thisisthesolutionnowadoptedbythe
InternationalWorkingGrouponNomenclatureandthatwhichwasadvocatedby
theconsensusstatementpreparedonbehalfoftheSocietyofThoracic
Surgeons.7Theapproachrecognizestheneedalsotodescribe,whenappropriate,
botharterialrelationshipsandinfundibularmorphology.Inthisway,all
potentialsforconfusionareavoided.
PrevalenceandEtiology
Transpositionwasresponsibleforupto20%ofcardiacdeathsininfancypriorto
theeraofsurgicalcorrection.Althoughnodefiniteetiologicfactorshavebeen
identified,theconditionisheldtobemorefrequentininfantsofdiabetic
mothers.8Maternalintakeofalcohol9orpoornutrition10duringpregnancymay
increasetheriskoftranspositionintheoffspring,whereasadditionoffolicacid
tothematernaldiethasbeenassociatedwithreducedrisk.11
Genetics
Malesareaffectedtwotothreetimesasfrequentlyasfemales.Transposition
doesnotseemtocoassociatewithknownmajorgeneticdisorders,andmost
casesaresporadic.Theincreasedpresenceofcopynumbervariationsinpatients
withtranspositionhasallowedforidentificationofcandidategenes.12Ingeneral,
genesaffectinglateralityandthenodalpathwayhavebeenassociatedwiththe
disease.13,14
