Andersons pediatric cardiology 680

Survival
Isomerismdoesimpactsurvival,withgreatermortalityinthosewithisomerism
whencomparedtothosewithsimilarcongenitalheartdefectsbutwithout
isomerism.Survivalhasimprovedwithtimeinisomerismpatientswith
functionallyuniventricularcirculationandbiventricularcirculation.Mortality
seemstobegreatestinthefirst3yearsoflifewhenallisomerismpatientsare
groupedtogether.Survivalat10yearsofageis61%andsurvivalat25yearsof
ageis35%.Ifonlythoseinthecurrenterabornafter2000areconsidered,there
is70%survivalat13yearsofage.Whenthesubsetsofisomerismarecompared,
thosewithleftisomerismtendtohavebettersurvivaluntilapproximately14
yearsofage.Survivalat5yearsofageis94%inthosewithleftisomerismand
76%inthosewithrightisomerism,whilesurvivalat10yearsofageis83%in
thosewithleftisomerismand64%inthosewithrightisomerism.Asmightbe
expected,thosewithbiventricularcirculationhaveincreasedsurvivalwhen
comparedtothosewithfunctionallyuniventricularcirculation.Inthosewith
biventricularcirculation,survivalat5and10yearsofageis89%and84%,
respectively.Obstructedpulmonaryvenousconnection,congenital
atrioventricularblock,moderateorgreateratrioventricularregurgitation,
presenceofacommonatrioventricularjunction,pulmonaryatresia,andneedfor
extracorporealmembraneoxygenationareallassociatedwithincreasedmortality
inthosewithisomerism.10–24


CardiacAnatomy
AtrialAnatomy
Structuralisomerism,strictlyenantiomerism,isseenwhenentitiesaremirror
imagesofeachother(Fig.26.1).Inthisrespect,theusualarrangementofthe
organswithinthebody,whencomparedtoitsmirror-imagedvariant,isan
exampleofbiologicenantiomerism(Fig.26.2).Itisnowestablishedbeyond
reasonabledoubtthatwithintheheart,whenassessedaccordingtotheextentof
thepectinatemusclesrelativetotheatrioventricularjunctions,itistheatrial

appendagesthatshowtheenantiomericfeatures.4Itis,however,onlytheatrial
appendagesthatareuniformlyisomeric.Oneofthefeaturesofisomerismis
anomalousvenoatrialconnections,althoughthepatternsofflowthroughthe
anatomicallyabnormallyconnectedveinscanbequasi-usualorquasi–mirror
imaged.Emphasisisplacedontheappendagessimplybecausethevenoatrial
connections,alongwithvestibularmorphologyandseptalstructure,areall
variable.Forexample,thepulmonaryveinsmaybeconnectedtothe
morphologicallyrightatrium,ortoanextracardiacsite.Theatrioventricular
junctionmaybeabsent,asintricuspidormitralatresia.Althoughtheatrial
septumhastypicalmorphologicallyrightandmorphologicallyleftsides,they
arenotalwaysthere.Thesevariablefeatures,followingthepreceptsestablished
bytheso-calledmorphologicmethod,cannotbeusedasreliableindicatorsof
morphologicallyrightnessorleftness.2Instead,theheartwithrightisomerism
willbecharacterizedbythepresenceofappendageseachhavingthemorphology
ofthenormalrightappendage.Theuniformlycharacteristicfeatureofsuch
rightnessistheextentofthepectinatemusclesaroundtheatrioventricular
junctions,sothattheymeetatthecrux(Fig.26.3).Theexternalfeaturesare
usuallydistinctive,butnotalwaysconstantwithbilateral,morphologicallyright
atrialappendagesrepresentedbyablunt,triangulartipandabroadjunctionwith
thevenouscomponent(Fig.26.4).Thisjunctionismarkedbyanextensive
grooveandcorrespondsinternallytoaprominentterminalcrest.Itistheextent
ofthepectinatemusclesthataretheuniversalcriterionformorphologically
rightnessonbothsidesoftheatriums(seeFig.26.3).Incontrast,intheheart
showingleftisomerism,eachoftheappendageswillhavethecharacteristic
morphologyofthenormalleftappendage,withthepectinatemusclescontained
withinthetubularappendages,theposteriorvestibularareasbeingsmoothon


bothsides,anddirectlyconfluentwiththevenouscomponents(Fig.26.5).The
tubularappendageofthemorphologicallyleftappendagehasanarrowor

constrictedjunctionwiththesmooth-walledcomponentoftheatrium(Fig.26.6).
Thepectinateridgesmayextendmorelaterallythantheconstrictedjunctionof
theappendage,buttheyarealwayssignificantlymorelimitedintheirextentthan
themorphologicallyrightatrium(compareFigs.26.3and26.5).Althoughthe
majormorphologicfeaturesofisomericappendagesaretobefoundinternally,
theexternalfeaturesarealsousuallydistinctive.Thepresenceofbilateral
triangular,asopposedtobilateraltube-like,appendages,however,isnot
universallypresent.Itistheextentofthepectinatemusclesthatistheuniversal
criterionformorphologicallyisomerismoftheappendages(Fig.26.7).The
arrangementoftheappendagesisinmostcasesharmoniouswiththe
arrangementofthethoracicorgans.Discordancebetweenpulmonary
arrangementandthatoftheappendages,however,isnotuncommon.Such
discordancecanalsobefoundinpatientswithnormalhearts.Forexample,inthe
syndromeofbiliaryatresiawithmultiplespleens,itispossibletofindbronchial
isomerism,butusualatrialarrangement.25,26Themorphologyoftheappendages
isthestartingpointofongoingsequentialanalysis,buttakingcaretonotethe
arrangementoftheothersystemsoforgansifdiscrepanciesareidentified.

FIG.26.1 Objectsthataremirrorimagesofeachother.Thisisthe
essenceofstructuralisomerism,properlydescribedasenantiomerism.