Andersons pediatric cardiology 979
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nonadjacentaorticsinusandlookingtowardthepulmonarytrunk(Fig.37.5).
Irrespectiveoftherelationshipsofthearterialtrunks,thesinusessupportingthe
coronaryarteriesarealwayslocatedtotherightandlefthandsoftheobserver.
Thesinusasseentotherightisuniversallyknownassinus1,whilethattothe
leftissinus2.15Allpatternsarethenaccountedforonthebasisofwhetherthe
right,circumflex,andanteriorinterventriculararteriesarisefromsinus1orfrom
sinus2.Mostusually,thearteriesarisewithintheaorticsinusesoratthelevelof
thesinutubularjunction,albeitusuallyeccentricallyplacedwithinthesinus.In
someinstances,thearteriescantakeahighoriginabovethesinutubularjunction.
Ofmoresignificanceisthearrangementwhenthearteriestakeatangential
coursethroughtheaorticwall,crossingtheattachmentsofthevalvarleafletsat
thesinutubularjunction.Thisistheso-calledintramuralorigin.16Inadditionto
sinusalorigin(Fig.37.5),epicardialcourseisalsoimportant,inparticular
retropulmonaryoranteroaorticlocationofanyofthethreemajorcoronary
arteries.17Thearterytothesinusnodeisoffurthersignificance.Itcanarisefrom
theinitialcourseofeithertherightorthecircumflexcoronaryarteries,oritcan
takeadirectoriginfromoneorotherofthefacingaorticsinuses.However,its
mostimportantvariationiswhenitcrossesthelateralmarginoftherightatrial
appendage.Insuchalateralposition,itisatsurgicalriskduringastandard
atriotomy.
FIG.37.5 Potentialvariabilityoftheaorta,whenpositionedanteriorly,
relativetothepulmonarytrunk.Withthisdegreeofvariability,itisnot
possibletoaccountforthelocationoftheaorticsinusesintermsofrightor
leftcoordinates,oranteriororposteriorcoordinates,withoutdescribing
eachheartseparately.Becausethecoronaryarteriesalwaysarisefromthe
sinusesclosesttothepulmonarytrunk,thesesinusescanalwaysbe
distinguishedasbeingtotherighthandoftheobserverstandinginthe
nonadjacentsinusandlookingtowardthepulmonarytrunk,notedassinus
1,ortothelefthand,notedassinus2.
VentricularSeptalDefect
Themostsignificant,andfrequentlyoccurring,associatedlesionintransposition
isaventricularseptaldefect.15Aswithsuchdefectsfoundinthesettingof
concordantventriculoarterialconnections,thesemaybesmall,large,ormultiple,
andtheycanbelocatedwithinanypartoftheventricularseptum(Fig.37.6).
Themostcharacteristicdefectsarethosethatopenbeneaththeventricular
outlets,withthemuscularoutletseptumbeingmalalignedrelativetotherestof
theventricularseptumandlocatedwithintherightventricle.Suchdefects,which
occupyasubpulmonarypositionwhenseenfromtheleftventricle,mayhavea
muscularposteroinferiorrim(Fig.37.7B)ormayextendtobecome
perimembranous.
FIG.37.6 Asisthecasewithinterventricularcommunicationsinthe
otherwisenormalheart,thosefoundinpatientswithtranspositioncanbe
characterizedasbeingmuscular,perimembranous,ordoublycommitted.
Themusculardefectscanbepositionedtoopentotheinlet,theapical
component,ortheoutletoftherightventricle.Perimembranous
communicationsarecentral,butthey,too,canextendtoopentotheright
ventricularinletoroutlet,thelatterinthesettingofmalalignmentbetween
theapicalseptumandtheoutletseptum.
