Andersons pediatric cardiology 1308
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questionableifangiographyisnowrequiredfordiagnosis.Interpretationofthe
images,considereddifficultinthepast,shouldnowbeverymucheasier.Evenin
potentiallysuitablecases,survivorsofattemptedseparationhavethusfarbeen
rare.Aswithexteriorizationoftheheart,thesituationmustbeanticipated
rapidlytoimprove,dependingofcourseonthedegreeoffusionofthecardiac
structures,andtheseverityoftheintracardiaclesionsineachtwin.
AbnormalPositioningoftheHeart
Theheartisnormallylocatedinthemediastinum,withone-thirdofitsbulkto
theright,andtwo-thirdstotheleftofthemidline.Withthisarrangement,the
apexusuallypointsinferiorlyandtotheleft.Thiscombinedpatternis
traditionallydescribedas“levocardia.”Theheartcanbedeviatedfromthis
position,oritsapexbepointedinanunexpecteddirection,forvariousreasons,
andnotalwaysbecauseofacongenitalcardiacmalformation.Forexample,the
heartcanbepushedtotherightbyaspace-occupyinglesionintheleftlungor
leftpleuralcavity,suchashyperinflationoftheleftlung,orpleuraleffusionand
pneumothoraxinvolvingtheleftpleuralcavity.Theheartcanalsobepulledto
therightwhentherightlungisunderdevelopedorcollapsed.Anabnormal
rightwardpositionoftheheartisalsotypicallyseeninassociationwithright
pulmonaryhypoplasiainscimitarsyndrome,ligamentousorductaloriginof
rightpulmonaryartery,oratresiaofstenosisoftherightpulmonaryvein.
Nonetheless,theabnormalpositioninitselfdoesnotnecessarilyimplyan
abnormalityoftheheart.Normalindividualswithmirror-imagedarrangementof
theorgansusuallyhavearight-sidedheart.Thereforewhenassessingthe
significanceofaright-sidedheartoraheartwithitsapexpointingtotheright,it
isnecessarytotakeaccountofallthesevariousfeatures.Severalquestions
shouldbeasked.Whatistheoverallarrangementoftheorgans?Istherean
abnormalityofthelungsorthethoraciccontents?Ifpresent,isitofcongenitalor
acquiredetiology?Istheheartitselfabnormallystructured,orareitschambers
grotesquelyenlarged?Onlywhenthesequestionshavebeenposed,and
answered,canthesignificanceofanabnormallypositionedheartbefully
appreciated.Attemptstocompressallthisinformationintoshortphrasesor
singlewordshaveledtocomplexandconfusingterms,suchasdextrocardia,
levocardia,dextroversion,levoversion,anddextroposition.21Ourpreferenceis
toavoidusingthesecrypticconventions.
Amuchsimplerapproachwhenconsideringtheabnormallypositionedheart,
isfirsttoaccountforitsoveralllocation.Thiscanbeleft-sided,central,orrightsided.Itisnecessarytoaccountfortheorientationofitsapex,whichcan
similarlybeleft-sided,central,orright-sided.Alllocationscanbecategorized
solelyintermsofthepositionoftheheart,andtheorientationofitsapex.This
information,ofcourse,mustbeplacedinthecontextoftheoverallarrangement
ofthethoracicandabdominalorgans,andthepresenceofacquiredorcongenital
diseaseofeithertheheartorthelungs.Thereforeabnormalpositioningofthe
heartshouldnolongerberegardedasadiagnosisinitsownright.Findinga
right-sidedheart,forexample,givesnoclueastowhatishappeninginsidethe
organ.Theheartitselfmaybeentirelynormal.Thedescriptionofanabnormal
locationisbutonepartoffullsequentialsegmentalanalysis(seeChapter1).
Nonethelesscertainwell-recognizedlesions,orcombinationsoflesions,are
associatedwithright-sidedhearts,orleft-sidedheartsinthosewithmirror
imagery.Asalreadyemphasized,theheartistypicallyright-sidedinassociation
withhypoplasiaoftherightlunginthescimitarsyndromeanditsvariants,which
isalsoknownasthebronchopulmonaryforegutmalformation.22Rightward
displacementoftheheartisalsoseeninassociationwithligamentalductalorigin
oftherightpulmonaryartery,withunilateralabsenceoftherightpulmonary
artery,andwithunilateralatresiaorstenosisoftherightpulmonaryveins.The
heartisalsoright-sidedinwelloverathirdofindividualswhohaveanisomeric
arrangementoftheirorgans(seeChapter22).Thesinglelesionmostassociated
witharight-sidedheart,orleft-sidedheartwithmirror-imagedarrangement,is
congenitallycorrectedtransposition(seeChapter38).Atbest,thesearecluesto
thefinaldiagnosis.Thevarietyoflesionsthatcanexistwhentheheartis
abnormallypositionedisprotean.
