Andersons pediatric cardiology 58
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FIG.1.12 Hearthavinganatrioventricularseptaldefectwithcommon
atrioventricularjunction(bracket).However,thepresenceofthecommon
junctiondoesnotdisguisethefactthateachatriumisjoinedtoitsown
ventricleacrosspairedjunctions,albeitnowguardedbyacommonvalve.
Oneofthejunctionsmaybeblockedbyanimperforatevalvarmembrane,but
thisdoesnotalterthefactthat,insuchasetting,therearestilltwopotential
atrioventricularconnections(Fig.1.13).
FIG.1.13 Atrioventricularjunctionssectionedinfour-chamberfashionina
heartwithcombinedtricuspidandpulmonaryatresia.Inthisinstance,
unusually,thetricuspidatresiaistheconsequenceofanimperforateright
atrioventricularvalve.Theatrioventricularconnectionsthereforeare
potentiallyconcordant(comparewithFig.1.14).RV,Rightventricle.
Insomehearts,thispossibilityisnotfulfilled.Thisisbecauseoneofthe
connectionsiscompletelyabsent.Inthissettingtheatrialmyocardiumonthat
sidehasnoconnectionwiththeunderlyingventricularmyocardium,being
separatedfromtheventricularmassbythefibrofattytissuesofthe
atrioventriculargroove.Thisarrangementisthemostcommonpatternproducing
atrioventricularvalvaratresia(Fig.1.14).
FIG.1.14 Aheart,withtheusualformoftricuspidatresia,sectionedin
four-chamberfashion.However,onlythreechambersareseen.Thisis
becausetheessenceoftypicaltricuspidatresia,andmanypatientswith
mitralatresia,isabsenceofanatrioventricularconnection,inthisinstance
therightatrioventricularconnection(dottedline).
Whenatrioventricularconnectionsaredefinedinthisfashion,allheartsfit
intooneofthreegroups.Inthefirstgroup,byfarthemostcommon,thecavity
ofeachatrialchamberisjoinedactuallyorpotentially,butseparately,tothatof
anunderlyingventricle.Thefeatureofthesecondgroupisthatonlyoneofthe
ventricles,ifindeedtwoarepresent,isincommunicationwiththeatrialcavities.
Thereisanevenrarerthirdgroup.Thisisseenwhenoneatrioventricular
connectionisabsent,andthesolitaryatrioventricularjunction,viaastraddling
valve,isconnectedtotwoventricles.Thisarrangementisuniatrialbut
biventricular.
Therearethreepossiblearrangementsinthoseheartswitheachatriumjoined
toitsownventricle;inotherwords,therearethreetypesofbiventricular
atrioventricularconnection.Thesedependonthemorphologyofthechambers
connectedtogether.Thefirstpatternisseenwhentheatriumsarejoinedto
morphologicallyappropriateventricles,irrespectiveofthetopologyor
relationshipoftheventriclesorofthemorphologyofthevalvesguardingthe
