Andersons pediatric cardiology 55
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position.Componentmake-up,trabecularpattern,topology,andsizeare
independentfeaturesoftheventricles.Onoccasion,allmayneedseparate
descriptiontoremoveanypotentialforconfusion.
Onlyrarelywillheartsbeencounteredwithasolitaryventricle.Sometimes
thismaybebecausearightorleftventricleissosmallthatitcannotbe
recognizedwithusualclinicalinvestigatorytechniques.Nonetheless,thereisa
thirdpatternofapicalventricularmorphologythatisfoundinheartspossessinga
trulysingleventricle.Thisiswhentheapicalcomponentisofneitherrightnor
lefttypebutisverycoarselytrabeculatedandcrossedbymultiplelargemuscle
bundles.Suchasolitaryventriclehasanindeterminatemorphology(Fig.1.6).
FIG.1.6 Heartopenedinclamshellfashiontoshowthatboth
atrioventricularvalvesenterthesameventricularchamber,whichalso
givesrisetobothoutflowtracts.Wewereunabletofindasecond
ventricularchamberinthisexample.Theexceedinglycoarseapical
trabeculationsandtheabsenceofthesecondchamberidentifythisheart
ashavingasolitaryventricleofindeterminatemorphology.Thisistheonly
true“single”ventricle.
Analysisofventriclesonthebasisoftheirapicaltrabeculationsprecludesthe
needtouseillogicallytheterms“singleventricle”or“univentricularheart”for
descriptionofthoseheartswithonebigandonesmallventricle.Thesehearts
mayproduceafunctionallyuniventriculararrangement,butallchambersthat
possessapicaltrabecularcomponentscanbedescribedasventricles,betheybig
orsmallandbetheyincompleteorcomplete.Anyattempttodisqualifysuch
chambersfromventricularstatemustleadtoasystemthatisartificial.Only
heartswithatrulysolitaryventricleneedbedescribedasuniventricular,albeit
thattheconnectionsoftheatrioventricularjunctionscanbeuniventricularin
manymorehearts.
Whendeterminingthemorphologyofthegreatarteries,nointrinsicfeatures
enableanaortatobedistinguishedfromapulmonarytrunkorfromacommonor
solitaryarterialtrunk.Nonetheless,thebranchingpatternofthetrunks
themselvesissufficientlycharacteristictopermitthesedistinctions(Fig.1.7).
FIG.1.7 Thebranchingpatternofarterialtrunkspermitstheirdistinction.
Thesolitaryarterialtrunkisdescribedwhentheintrapericardialpulmonary
arteriesareabsentbecauseinthissettingitisimpossibletodetermine,had
theybeenpresent,whethertheywouldhavetakenoriginfromtheheart,
makingthetrunkanaorta,orfromthetrunkitself,inwhichcasethere
wouldhavebeenacommonarterialtrunkwithpulmonaryatresia.
Theaortagivesrisetoatleastonecoronaryarteryandthebulkofthe
systemicarteries.Thepulmonarytrunkgivesrisedirectlytoboth,oroneor
other,ofthepulmonaryarteries.Acommontrunksuppliesdirectlythecoronary,
systemic,andpulmonaryarteries.Asolitaryarterialtrunkexistsintheabsence
oftheproximalportionofthepulmonarytrunk.Insuchcircumstances,itis
impossibletostatewithcertaintywhetherthepersistingtrunkiscommonor
aortic.Evenintherarecasesthathavetransgressedoneoftheserules,
examinationoftheoverallbranchingpatternhasalwayspermittedusto
distinguishthenatureofthearterialtrunk.
AtrialArrangement
Thecornerstoneofanysystemofsequentialanalysismustbeaccurate
establishmentofatrialarrangementbecausethisisthestartingpointfor
subsequentanalysis.Whenarrangementoftheatriumsisassessedaccordingto
themorphologyofthejunctionoftheappendageswiththerestoftheatriums,19
Thereareonlyfourpossiblepatternsofarrangement(Fig.1.8)becauseallhearts
havetwoatrialappendages,eachofwhichcanonlybemorphologicallyleftor
right.
FIG.1.8 Whenanalyzedonthebasisoftheextentofthepectinate
musclesrelativetotheatrioventricularvestibules(seeFig.1.2),thereare
onlyfourpossiblewaysinwhichthetwoatrialappendagescanbe
arranged.However,notethatthevenoatrialconnectionscanshowmarked
variation,particularlyintheisomericsettings,alsoknowncollectivelyas
visceralheterotaxy.
Themostcommonistheusualarrangement,alsocalledsitussolitus,inwhich
themorphologicallyrightappendageisright-sidedandthemorphologicallyleft
appendageisleft-sided.Thesecondarrangement,whichisveryrare,isthe
mirrorimageoftheusual.Itisoftencalledsitusinversus,eventhoughtheatrial
chambersarenotupsidedown.Inthesetwoarrangements,theappendagesare
lateralized,withthemorphologicallyrightappendagebeingtooneside,andthe
morphologicallyleftappendagetotheother.Thetwootherarrangementsdonot
