Andersons pediatric cardiology 794
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Fig.31.2,right).
FIG.31.2 Differencebetweentheposteriorandanteriorcomponentsof
thestructuresthatmakeupthetissuesinterposedbetweentherightand
leftatrioventricularjunctionsinthenormalheart.Left,Cutacrossthe
atrioventricularmuscularsandwich,withthesubepicardialfatwithinthe
inferioratrioventriculargrooveextendingtoseparatetheatrialand
ventricularmuscularcomponents.Right,Cutacrossthemembranous
septum,withitsatrioventricularcomponentformingtherightwardwallof
thesubaorticoutflowtract.
Thisseptalcomponentisalsoanintegralpartofthecentralfibrousbody,
whichformstherightwardwalloftheleftventricularoutflowtract.15Inthe
normalheart,theleftventricularoutflowtractinterposesbetweenthemitral
valvarorificeandtheseptum(Fig.31.3,left).Intherightventricularorifice,one
oftheleafletsofthetricuspidvalveisadherenttotheventricularseptumovera
considerablearea.Thesearrangementsarepertinenttothenamingoftheleaflets
ofthenormalandabnormalvalves.Inthemitralvalvarorifice,thecurtainof
leaflettissueisdividedbyanobliquelyorientatedlineofappositionintoashort
andsquareleaflet,besttermedtheaorticleafletbutoftentermedtheanterior
leaflet.16Theotherleafletismoreextensiveintermsofitscircumferential
attachmentbutmuchshallower.Thisisthemuralorposterior,leaflet.Thetwo
leafletscloseoverasolitaryzoneofapposition(seeFig.31.3,left).Thenormal
tricuspidvalvehasthreeleaflets,whicharelocatedintheanterosuperior,septal,
andinferiorormuralpositions.Thedimensionsoftheseptalaspectofthe
ventricularmassalsovarybetweenheartswithseparateasopposedtocommon
atrioventricularjunctions.Inthenormalheart,thedistancefromtheattachment
ofthemitralvalveatthecruxtotheventricularapex,ortheinletdimension,is
muchthesameasthatfromtheventricularapextotheanterosuperiorattachment
oftheleafletsoftheaorticvalve,thisbeingtheoutletdimension(Fig.31.4A).
Theessenceofheartswithanatrioventricularseptaldefectandacommon
atrioventricularjunctionisdisproportionbetweentheseinletandoutlet
dimensions.
FIG.31.3 Short-axiscutsoftheventricularmass,asviewedfromthe
apicalaspect,showingthedifferencesbetweentheseparate
atrioventricularjunctionsofthenormalheart(left)andthecommonjunction
foundinheartswithdeficientatrioventricularseptation(right).Notethatthe
leafletsoftheleftatrioventricularcomponentofthecommonatrioventricular
junction,likethenormaltricuspidvalve,closeintrifoliatefashion.This
shouldbecomparedwiththetwoleafletsofthemitralvalve,whichclose
alongasolitaryzoneofapposition(double-headedarrowatleft).
FIG.31.4 Normalheart(A)andheartwithatrioventricularseptaldefect
withcommonatrioventricularjunction(B)illustratingthedifferencesinthe
inlet(bluearrows)andoutlet(redarrows)dimensionsoftheleftventricular
septalsurfaces.Notealsothattheventricularseptumisscoopedinthe
heartwithdeficientatrioventricularseptation(yellowarrow).
BasicMorphologyofAtrioventricularSeptal
Defects
ApartfromtheGerbodedefect(seelater),theessentialmorphologicingredient
ofheartsnowusuallydescribedashavingatrioventricularseptaldefectsisthe
presenceofacommonatrioventricularjunction.17Thisjunctioniscommontoall
fourcardiacchambersinallhearts.Therearenointermediateortransitional
arrangements.Thejunctionalarrangementsarematchedbydifferencesinthe
arrangementofthefibrousskeleton,withthecontinuitybetweenthe
membranousseptumandtherightfibroustrigonefundamentallydisturbedwhen
thereisacommonatrioventricularjunction(Fig.31.5).
