Andersons pediatric cardiology 795
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FIG.31.5 Differencesinarrangementofthefibrousskeletoninthenormal
heart(left)comparedwithheartswithdeficientatrioventricularseptation
(right).Thesedifferencesarefoundinallheartswithatrioventricularseptal
defectandcommonatrioventricularjunction.Intermsofjunctional
anatomy,therearenointermediateortransitionalvariants.
Thesedifferencesinjunctionalarchitectureunderscoredeparturesfrom
normalityinatleastfourofthefeaturesalreadyenumeratedascharacteristicof
heartswithseparaterightandleftatrioventricularjunctions.First,almostalways
butnotuniversally,thereisadefectattheanticipatedsiteofthestructuresthat
usuallyinterposebetweentherightatriumandtheleftventricle.Theseptal
deficiencyiscomparableirrespectiveofwhetherthereisacommonvalvar
orificewithinthecommonjunction(Fig.31.6,right)orthereareseparate
atrioventricularvalvarorificesfortherightandleftventricles(Fig.31.6,left).
Thearrangementwithseparatevalvarorifices,butacommonatrioventricular
junction,isalsoknownasan“ostiumprimumdefect.”Theseptaldeficiencyis
betweentheleadingedgeoftheatrialseptumandthecrestofthemuscular
ventricularseptum,towhichthevalvarleafletsareattached(seeFig.31.1,
right).
FIG.31.6 Comparisonofthearrangementsoftheseptalcomponentsin
heartswithdeficientatrioventricular(AV)septationandcommon
atrioventricularjunction,butwithseparatevalvarorificesfortherightand
leftventricles(left)asopposedtoacommonvalvarorifice(right).Inthe
heartwithseparatevalvarorifices,becausethebridgingleafletsofthe
commonvalveareattachedtoeachotherandtothecrestofthescoopedoutventricularseptum,thepotentialforshuntingacrosstheatrioventricular
septaldefectisconfinedatatriallevel,eventhoughmuchoftheshuntingis
belowthelevelofthecommonatrioventricularjunction(redarrow).Inthe
heartwiththecommonvalvarorifice,thereisthepotentialforshuntingat
bothatrialandventricularlevels.
Thesecondfeatureistheovalshapeofthecommonatrioventricularjunction
(seeFig.31.3,right).Irrespectiveofthenumberofatrioventricularvalvar
orificeswithinthejunction,theleftventricularoutflowtractisnotwedged
betweentheleftandrightatrioventricularannuli,asseeninthenormalheart.
Instead,theaorticorificeisanterosuperiortothecommonjunction.Thejunction
isjustascommonintheheartshavingseparatevalvarorificesfortherightand
leftventricles(Fig.31.7,left)aswhenthereisacommonvalvarorifice(Fig.
31.7,right).
FIG.31.7 Shortaxisoftheatrioventricularjunctionsasviewedfromthe
atrialaspectinheartswithseparatevalvarorificesfortherightandleft
ventricles(left)andacommonvalvarorifice(right).Thejunctionisjustas
commonandtheaortajustasunwedgedinbothexamples.Notethatthe
spacebetweenthebridgingleafletsintheheartwithseparatevalvar
orificesispartofthezoneofappositionbetweentheleaflets(reddashed
lineatright).
Sincethereisacommonatrioventricularjunctionandalackofanyseptal
atrioventricularmuscularcontiguity,thethirdfeaturethatdiffersfromthe
normalisthearrangementofthevalvarleafletsthatguardthecommonjunction.
Theseleaflets,irrespectiveofwhethertheyguardacommonatrioventricular
orificeorseparateorificesfortherightandleftventricles,bearscant
resemblancetothearrangementoftheleafletsofthenormalmitralandtricuspid
valves(seeFig.31.7).Whendescribingthevalvesandcomparingthemwiththe
arrangementseeninthenormalheart,thekeyfeatureistheboundariesofthe
individualleaflets.Thesearebestassessedwhenthevalveisseeninitsclosed
position.Studiedinthisfashion,theoverallcurtainofleaflettissueinhearts
havingthephenotypicfeatureofanatrioventricularseptaldefectwithacommon
atrioventricularjunctioncanbeseparatedintofivediscretecomponents(Fig.
31.8).
