Andersons pediatric cardiology 1816
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FIG.69.22 Combinationsofthesidednessofthestraddling
atrioventricular(AV)valve(columns)andtheright-sidedasopposedtoleftsidedventriculartopology(rows)thatcanbefoundwhenthereisabsence
ofoneAVconnectionbutthesolitaryAVvalveisstraddlingandoverriding.
ThesecombinationsproduceAVconnectionsthatareuniatrialbut
biventricular.Insuchinstances,bothventricleswillbeincompletetoa
greaterorlesserextent,butoneofthemisusuallydominant.
UnbalancedAtrioventricularSeptal
Defect
Thespectrumofmalformationdescribedforstraddlingandoverridingofeither
themitralortricuspidvalvescanbereplicatedinthesettingofacommon
atrioventricularvalve.Itissometimesthought,furthermore,thatthestraddling
solitaryvalveisa“common”entity.This,ofcourse,cannotbethecase,sincethe
solitarystraddlingvalveguardseithertherightortheleftatrioventricular
junction.Forthevalvetobecommon,itmustguardtheentiretyofboth
atrioventricularjunctions.Suchcommonvalves,asfoundinatrioventricular
septaldefectwithcommonatrioventricularjunction,usuallystraddlethecrestof
theventricularseptum,withtheirbridgingleafletssupportedbytendinouscords
inbothventricles.However,insomeheartswithdouble-inletventricle,a
commonatrioventricularvalvecanbeexclusivelysupportedbyeitherthe
dominantright(seeFig.69.18B)orthedominantleftventricle.Thedegreeof
overridingofthecommonvalveproducesthespectrumofunbalanced
atrioventricularseptaldefects.Thecommonvalvebeingexclusivelycommitted
tooneorotherventriclecanbeconsideredtorepresenttheextremeformof
atrioventricularseptaldefectwithacommonatrioventricularjunction.
Determiningtheextentofoverriding,andhencetherelativesizeofthetwo
ventricles,remainsoneofthemostdifficulttasksforthepediatriccardiologist.
Thisisbecauseitisthesizeoftheincompleteventricle,particularlyinthe
settingofrightventriculardominance,thatdeterminestheoptionsfor
biventricularasopposedtofunctionallyuniventricularrepair.Theseproblems,
andtheunderlyinganatomicsituations,arediscussedinChapter32.
ComplexDouble-OutletVentricle
AsdiscussedatlengthinChapter39,surgicalrepairofdouble-outletventricle
dependsontunnelingtheinterventricularcommunicationtooneorotherofthe
ventricularoutflowtracts.Thisisusuallypossiblewhenthecommunicationisin
subaortic,subpulmonary,ordoublycommittedlocations.Itcanfrequentlybe
achievedevenwhen,atfirstsight,thecommunicationmayseemtobeina
noncommittedposition.However,inothercircumstances,featuressuchas
anomalousattachmentofthetensionapparatusoftheatrioventricularvalvesmay
conspireastorenderimpossibletheconstructionofaninterventriculartunnel.
Thisisalsolikelytobethecasewhentheinterventricularcommunicationis
withintheapicalcomponentofthemuscularseptumoropenstotheinletofthe
rightventricle.Thesecircumstancesareagainlikelytotiltthebalanceofsurgical
repairinfavorofconstructionoftheFontancirculation.Theanatomicfeatures
underscoringthesedecisionsarediscussedinChapter40.
