Andersons pediatric cardiology 792
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AtrioventricularSeptalDefects
TjarkEbels,JustinT.Tretter,DianeE.Spicer,RobertH.Anderson
Abstract
Thefocusofthischapteristhevariantofatrioventricularseptaldefectin
whichthephenotypicfeatureisthecommonalityoftheatrioventricular
junction.Thepresenceofthecommonjunctionreflectsnotonlyfailureof
formationofthenormalatrioventricularmembranousseptumbutalso
absenceofthemuscularsandwichthatproducesthenormaloffsetting
betweentheleafletsofthetricuspidandmitralvalves.Thecommon
atrioventricularjunctionitselfcanbeguardedbyacommonatrioventricular
valveoracommonvalvewithdualorifices.Thecommonvalvehasfive
leaflets,twoconfinedtotherightventricle,onetotheleftventricle,andthe
othertwobridgingtheventricularseptum.Therelationshipbetweentheleft
ventricularcomponentsofthebridgingleafletsandtheleafletconfinedto
theleftventricleproducesatrifoliateleftatrioventricularvalve,withthe
thirdcomponent,themuralleaflet,guardinglessthanone-thirdofthe
circumferenceoftheleftatrioventricularorifice.Thespacebetweentheleft
ventricularcomponentsofthebridgingleaflets,althoughpreviously
describedasa“cleft,”isinrealitythezoneofappositionbetweenthem.
Therelationshipbetweenthebridgingleafletsandtheseptalstructures
underscoresthepotentialforshuntingacrosstheatrioventricularseptal
defect.Therelationshipbetweenthecommonjunctionandtheatrialand
ventricularchambersaccountsfortheconceptsofdominantasopposedto
balancedsharingofthejunction.Multipleassociatedlesionscanfurther
complicatethemorphologicarrangement.Havingaddressedtheissuesof
morphogenesis,prevalence,andclinicalfeatures,wediscussandillustrate
thetechniquesusedtodiagnosetheanatomicvariations.Weconcludethe
chapterwithconsiderationsofthevariousapproachestosurgicalcorrection
andareviewoftheimpactofsuchcomplicatingfeaturesasthepresenceof
trisomy21.
KeyWords
Commonatrioventricularjunction;trifoliateleftatrioventricularvalve;
ostiumprimumdefect;surgicalcorrection;Downsyndrome
Thereisagroupoflesionsunifiedbytheanatomichallmarkofacommon
atrioventricularjunctioncoexistingwithdeficientatrioventricularseptation.The
keytotheirdifferentiationfromotherpotentiallyrelateddefectsisthepresence
ofthecommonjunction,includingthearrangementofthefibrousskeletonofthe
heart,whichisfundamentallydifferentfromthemorphologyfoundinthe
normalheart.Inclinicalterms,itisprobablytheinfluenceofthisabnormal
architectureoftheatrioventricularvalvesthatisthemostprominentfeature.In
thisrespect,thereisacommonatrioventricularjunctionirrespectiveofwhether
thereareseparateatrioventricularvalvarorificesfortherightandleftventricles
—withthelatterlesiontraditionallydescribedastheostiumprimumdefect—or
whetherthevalveitselfisalsoacommonstructure,oftendescribedasthe
completeformofthemalformation.Asweshow,theabnormalmorphologyof
theventricularmassandtheatrioventricularjunctionismoreorlessconstant
withintheoverallgroup,thuscallingintoquestionthenotionofdistinguishing
betweenpartialandcompletevariants.Alsowedescribethelesionshere—
describedpreviouslyasendocardialcushiondefectsoratrioventricularcanal
malformations—simplyasatrioventricularseptaldefects.1Sincethepublication
ofthepreviouseditionofthistext,thistermhasslowlycometoachieve
recognitionasbeingthemostaccuratedescriptor.Veryrarely,heartswith
deficientatrioventricularseptationcanexistwithotherwisenormal
atrioventricularjunctions.2Thesearetheso-calledGerbodedefects,whichare
describedinChapter32,onventricularseptaldefect.Patientswithallthe
stigmatadescribedinthepresentchaptercanalsobefound,againrarely,when
theseptalstructuresareintact,3,4presumablyduetospontaneousclosureofa
preexistingatrioventricularseptaldefect.5Notwithstandingthesepotential
caveats,itremainsourconvictionthatatrioventricularseptaldefectisthebest
defaultoptionforthisimportantgroupofmalformations.Forprecision,itis
necessaryalsotospecifythepresenceofthecommonatrioventricularjunction
andtoindicatespontaneousclosureinthoserareinstanceswhentheseptal
structuresareintactdespitethepresenceofthecommonjunction.5
