Andersons pediatric cardiology 1814

atrioventricularvalve(B).Notethelocationoftheincompleteleftventricle
(LV)in(B).Itislocatedposteroinferiorlyrelativetothedominantventricle
and,asshown,isusuallyleft-sided.Sinceitislocatedposteroinferiorly,itis
notseenintheheartshownin(A).


StraddlingAtrioventricularValves
Patientswithstraddlingofoneorotheratrioventricularvalve,orrarelyboth
atrioventricularvalves,formaspectrumbetweenuniventricularand
biventricularatrioventricularconnections.Thisisbecausethestraddlingofthe
atrioventricularvalvartensionapparatusisalmostalwaysassociatedwith
overridingoftheatrioventricularjunction.Theextentoftheoverridingjunction
supportedbythedominantasopposedtotheincompleteventriclewilldetermine
whethertheatrioventricularconnectionsareeffectivelydoubleinletor
biventricular.Theincompleteventriclewillitselfbeappreciablylargerwhenthe
connectionsarebiventricular,butthemerepresenceofstraddlingofthetension
apparatuscanbesufficienttotiltthestrategiesforsurgicalrepairtowardthe
Fontanoptiondespitethepresenceofaventricularcavityandmassthatmaybe
normalinsize.Eithertherightorleftatrioventricularvalvecanstraddleor
override,anddependingontheventriculartopology,thiscanproducespectra
extendingfromeitherconcordantordiscordantconnectionstodouble-inletleft
ventricleordouble-inletrightventricle(Figs.69.19and69.20).Itisstraddlingof
thetricuspidvalvethatleadstodouble-inletleftventricle,whereasstraddlingof
themitralvalveisassociatedwithaspectrumleadingtodouble-inletright
ventricle.Whethertheatrioventricularconnectionsareconcordantordiscordant
ineithersituationdependsonthecombinationsofatrialarrangementand
ventriculartopology.Inallinstances,however,thetricuspidvalvestraddlesand
overridestheinletpartoftheventricularseptum.Thishasimportant
consequencesforthedispositionoftheatrioventricularconductionaxis,evenif
theatrioventricularconnectionsarepotentiallyconcordant.Thisisbecause
overridingofthejunctionsupportingthemorphologicallytricuspidvalve

producesmalalignmentbetweentheatrialandapicalventricularsepta.Because
theapicalventricularseptumcarriestheatrioventricularconductionaxisonits
crest,thismeansthattheatrioventricularbundleisunabletomakecontactwith
theregularatrioventricularnodeattheapexofthetriangleofKoch.Instead,the
axistakesitsoriginfromananomalousatrioventricularnodeformedatthepoint
wherethemalalignedventricularseptummeetstheatrioventricularjunction(Fig.
69.21A).Whenthemitralvalvestraddlesandoverrides,itdoessothroughan
anterosuperiorseptaldefect,typicallyinthesettingofeithertranspositionor
double-outletrightventriclewithsubpulmonaryinterventricularcommunication.
Inthissetting,whentheatrioventricularconnectionsarepotentiallyconcordant,


theconductionaxismaintainsitsoriginfromtheregularatrioventricularnode.
Whenstraddlingofeitherthemitralortricuspidvalveisfoundinthesettingof
discordantatrioventricularconnections,however,theconductionaxisshouldbe
anticipatedtoarisefromananterolateralatrioventricularnode.However,there
canbeaslingofconductiontissuewhenitisthemitralvalvethatisstraddlingin
thissetting.

FIG.69.19 Spectrafoundinthesettingofstraddlingofthe
morphologicallytricuspidvalve.Theupperpanelsshowhow,whenthe
tricuspidvalveisright-sided,theatrioventricular(AV)connectionswith
minimalstraddlingareconcordant,whereaswithexcessivestraddlingand