Andersons pediatric cardiology 1059

Thereforeacommonarterialtrunkisoneformofsingleoutletfromtheheart.
Asamalformationinvolvingtheventriculoarterialjunctions,itmustbe
anticipatedtocoexistwithallpossiblesegmentalcombinations.Inalmostall
instances,nonetheless,therewillbeausualatrialarrangement,withconcordant
atrioventricularconnections.Examplescanbefoundincombinationwith
discordantatrioventricularconnectionsorwithabsenceoftheright
atrioventricularconnection.6Althoughtheatrioventricularjunctionsthemselves
areusuallyseparate,andguardedbymitralandtricuspidvalves,acommontrunk
canrarelybefoundinassociationwithanatrioventricularseptaldefectanda
commonatrioventricularvalve.Inthepresenceofthecommontrunk,thetruncal
valveisalmostalwaysconnectedacrosstheventriculoarterialjunctionswith
bothventricles,thevalvarorificeoverridingtheventricularseptalcrest,and
typicallywithitsleafletsinfibrouscontinuitywiththemitralvalveintheleft
ventricle(Fig.40.3).Suchabiventricularconnectionnecessitatesthepresenceof
ajuxtaarterialinterventricularcommunication.Thedefectisgenerallylarge.Its
flooristhecrestoftheventricularseptum,reinforcedontherightventricular
aspectbythelimbsoftheseptomarginaltrabeculation,orseptalband,andits
roofistheleafletsofthetruncalvalve.Theconeofspacesubtendedbythe
truncalvalvehasrightandleftventricularmargins,butitisusuallytheright
ventricularmarginthatisconsideredtorepresenttheventricularseptaldefect,
anditisthisspacethatisclosedbythesurgeonduringrepair.Inthemajorityof
cases,fusionoftheinferiorlimboftheseptomarginaltrabeculationwiththe
ventriculoinfundibularfoldalongthisrightventricularmarginproduces
musculardiscontinuitybetweentheleafletsofthetricuspidandthetruncal
valves(Fig.40.4,left).Intheabsenceofsuchfusion,thereiscontinuitybetween
theleafletsofthetricuspidandtruncalvalves,makingtheventricularseptal
defectperimembranous(seeFig.40.4,right).Whenpresent,thismuscularbarin
theposteroinferiormarginprotectsthespecializedaxisresponsiblefor
atrioventricularconduction.Inmostinstances,thereisalargedistancebetween
thecoaptingarterialvalvarleafletsandthecrestoftheseptumduringventricular
diastolewhentheleafletsareclosed.However,thisspacemaysometimesbe

reducedortheleafletsmayclosedirectlyontheseptalcrest(Fig.40.5,left).
Somehavedescribedthislatterarrangementasrepresentingan“intact
ventricularseptum.”7Thisissomewhatmisleadingbecause,eveninthis
arrangement,aseptaldeficiencyisseenattheventricularlevelwhenthetruncal
valveopensduringventricularsystole(seeFig.40.5,left).Furthermore,hearts
arefoundwhentheventricularseptumistrulyintact,thecommontrunkarising


inmostinstancesexclusivelyfromtherightventricle(seeFig.40.5,right).The
interventricularcommunicationcanalsoberestrictivewhenthecommontrunk
takesanexclusiveoriginfromoneortheotherventricle.Sucharestrictive
ventricularseptaldefectismorelikelytoproduceproblemswhenthetrunk
arisesexclusivelyfromtherightventricle(seeFig.40.3,right).

FIG.40.3 Left,Heartsectionedtoreplicatetheparasternallongaxis
echocardiographicsection.Itshowsthetruncalvalveoverridingthecrestof
themuscularventricularseptum,withthevalvarleafletssupportedinboth
ventricles.Notethefibrouscontinuitybetweentheleafletsofthetricuspid
andmitralvalves.Right,Incontrast,thishearthasthetrunkexclusively
supportedabovethemorphologicallyrightventricle,withacompletely
muscularsubtruncalinfundibulum.


FIG.40.4 Thepresenceorabsenceofamuscularrimalongthe
posteroinferiormarginoftheinterventricularcommunicationdetermines
whetherthedefectisconsideredtobeperimembranous.Left,The
ventriculoinfundibularfoldfuseswiththeposteroinferiorlimbofthe
septomarginaltrabeculation(yellowbars).Themuscularbarthusformed
(star)protectstheatrioventricularconductionaxisduringsurgical
correction.Right,Defectwithfibrouscontinuitybetweentheleafletsofthe

truncalandtricuspidvalves,puttingconductionaxis(dottedline)at
potentialriskduringsurgicalcorrection.