Andersons pediatric cardiology 797
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Attemptstocombinedescriptionsofthetwofeaturestogiveoneall-embracing
categorizationhaveproducedbewilderingarraysofdefinitionsforso-called
transitionalorintermediatelesions.Ifthetwofeaturesaredescribedseparately,
theneedtonominateintermediatecategoriesisavoided.Otherfeatures,
furthermore,areimportantinclinicalpresentation.Examplesaretheextentof
thesharingofthecommonatrioventricularjunctionbetweentheatrialand
ventricularchambersandthepresenceofassociatedlesions.Allofthesefeatures
requiredescription.
ArrangementoftheValvarLeafletsRelativetotheAtrioventricular
Orifices.
Thecurtainofvalvartissueguardingthejunctioninallheartswith
atrioventricularseptaldefectandcommonatrioventricularjunctionscanbe
describedintermsoffiveleaflets.Therelationshipbetweenthetwobridging
leafletsthemselvespermitsalloftheseheartstobeplacedintooneoftwogroups
withnointermediatecategories.Themajorityhaveaspacebetweenthetwo
bridgingleafletsandhencehaveacommonatrioventricularvalvarorifice(see
Fig.31.7,right).Thecomponentofthiscommonvalvecommittedtotheleft
ventriclealmostalwaysclosesinatrifoliatepattern(seeFig.31.9).Inaminority
ofhearts,thetwobridgingleafletsarethemselvesjoinedtoeachotherbya
connectingtongueofvalvartissue.Thisdividesthecommonatrioventricular
junctionintorightandleftcomponents(Fig.31.7,left),essentiallyproducing
dualorificeswithinthecommonjunction.Inmostinstances,shuntingacrossthe
defectinthissettingisconfinedtotheatriallevel,sincetheleafletsarealso
fusedtothecrestofthemuscularventricularseptum(Fig.31.6,left).Such
fusiontotheventricularseptum,however,isnotauniversalfeatureofheartsin
whichthecommonjunctionisdividedintorightandleftventricularcomponents
bytheunionbetweenthebridgingleaflets.Insomeinstances,thebridging
leafletscanbefusedtoeachother,thusdividingthevalvarorifice,butalsofused
totheundersideoftheatrialseptumsothatthepotentialforshuntingisrestricted
atventricularlevel.Thisisthe“atrioventricularcanal”typeofventricularseptal
defect,inrealityanatrioventricularseptaldefectwithshuntingconfined
exclusivelytotheventricularlevel(Fig.31.10,left).Inveryrareinstances,the
bridgingleafletscanbefused,producingseparatevalvarorificesfortheright
andleftventriclesbutwiththetongueofleaflettissuejoiningtheleaflets
attachedtoneithertheatrialnorventricularsepta(Fig.31.10,right).Intermsof
theoverallmorphologyofthecurtainofvalvartissue,therefore,allheartscanbe
dividedintothosewithacommonatrioventricularvalvarorificeguardingthe
commonjunctionandthoseinwhichthecommonjunctionisguardedby
separaterightandleftatrioventricularvalvesfortherightandleftventricles,
respectively.Thisfeatureisan“all-or-none”phenomenon.
FIG.31.10 Variationsinthepatternofarrangementofthebridgingleaflets
toeachotherandtotheseptalcomponents.Left,Commonvalvarorifice;
duringventricularsystole,thebridgingleafletsabuttheleadingedgeofthe
atrialseptum,thusconfiningshuntingatventricularlevel.Right,Heartin
whichthebridgingleafletsarefusedtoeachotherbutfailtoattachtoeither
theleadingedgeoftheatrialseptumorthescooped-outventricular
septum.Hencethepotentialforshuntingexistsatbothatrialand
ventricularlevels.AV,Atrioventricular.
PotentialforShuntingAcrosstheAtrioventricularSeptalDefect.
Itisthepotentialforshuntingacrosstheseptaldefectthatisprobablythesingle
mostimportantanatomicvariantinfluencingclinicalpresentation.Thisanatomic
variabilitydependsontherelationshipofthebridgingleafletsandofthe
connectingtongue,ifpresent,totheleadingedgeoftheatrialseptumontheone
hand,and,ontheotherhand,tothecrestofthescooped-outventricularseptum.
Inmostcasesthetwobridgingleafletsareattacheddirectlytoneitherseptal
componentastheybridgebetweentheventricles(seeFig.31.6,right).Inthis
arrangement,therefore,thepotentialexistsforshuntingatboththeatrialand
ventricularlevels,asitdoeseveniffusedbridgingleafletsfloatfreelywithinthe
septaldefect(seeFig.31.10,right).Theextentofventricularshuntingdepends
ontheproximityofthebridgingleafletstotheventricularseptalcrest.Ifthe
leafletsfloatfreely,therewillbeanextensiveinterventricularcommunication.
Shouldcordsfromtheseptalcresttightlytetheroneortheotherleafletorboth
leaflets,thepotentialforventricularshuntingcanbeseverelylimited.Very
rarely,inthepresenceofseparatesuperiorandinferiorbridgingleaflets,both
leafletsmaybefusedtotheventricularseptalcrest.Shuntingwilloccuronlyat
theatriallevel,eventhoughthereisacommonvalvarorifice.Thearrangement
inwhichthebridgingleafletsareattacheddirectlytotheventricularseptum,
however,istypicallyseenwhentheyareadditionallyattachedtoeachotherby
theconnectingtongue.Asdiscussed,thisarrangementgivesseparatevalvar
orificesfortherightandleftventricles,andproducestheostiumprimumdefect
(seeFig.31.6,left).Inaproportionofpatientswithseparaterightandleft
atrioventricularvalvarorifices,thebridgingleafletsmaybeattachedtoeach
otherbytheconnectingtongue,butintercordalspacesbeneaththetongueand
beneaththebridgingleafletscanpermitsmallinterventricularcommunications.
Onoccasionthetissueofthebridgingleafletscanalsoentirelyclosetheseptal
deficiency.Suchspontaneousclosureproducesaheartwithacommon
atrioventricularjunction,butlackingtheopportunityforshuntingacrossthe
preexistingatrioventricularseptaldefect.Intermsofoverallshuntingacrossthe
atrioventricularseptaldefect,therefore,thekeyfeatureistherelationship
betweenthebridgingleafletsandtheseptalstructures.Thisfeatureis
independentofthearrangementofthevalvarleafletsthatguardthejunction.
AbnormalitiesoftheLeftAtrioventricularValve.
Theessenceoftheleftatrioventricularvalveinheartswithatrioventricularseptal
defectandacommonatrioventricularjunctionisthatitclosesintrifoliate
fashion(seeFig.31.9).Apartfromitsresidencewithinthemorphologicleft
ventricle,theonlyanatomicaffinitieswiththemorphologicmitralvalvearethe
fabricofthevalve,andeventhisshowssignificantdifferences.21Theleftvalve,
likethemitralvalve,isitselfliabletobecongenitallymalformed.Thepresence
ofadditionalconnectingtonguesbetweentheleafletsofthevalvecanproduce
dualorifices.Rarely,shouldbridgesbefoundbetweenthemuralleafletandboth
bridgingleaflets,theleftvalvecanhavethreeorifices.Thepresenceofthese
tonguesofleaflettissueextendingbetweenadjacentleaflets,usuallybetween
oneofthebridgingleafletsandthemuralleaflet,andseparatingtheorificeinto
subordinatecompartments,iscomparabletothewaytheconnectingtongueitself
