Andersons pediatric cardiology 980
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FIG.37.7 Ventricularseptaldefectsinthesettingoftranspositionwith
malalignmentbetweentheoutletseptumandapicalseptum.(A)Theoutlet
septumismalalignedtotheright,openingtotherightventriclebetweenthe
limbsoftheseptomarginaltrabeculation(yellowbars).Notethemuscular
posteroinferiorrimtothedefect(star).(B)Inthisventricularseptaldefect
viewedanteriorlyandfromtheleftside,theoutletseptumismalaligned
posteriorlyintotheleftventricleandobstructsthesubpulmonaryoutflow
tract.VSD,Ventricularseptaldefect.
Theoutletseptumcanalsobemalalignedintotheleftventricle.Thisthen
narrowstheleftventricularoutflowtract,producingpulmonarystenosisin
associationwithoverridingandbiventricularconnectionoftheaorticvalve(Fig.
37.7B).Inthemorecommonmalalignmentdefects,asshownFig.37.7A,the
pulmonaryvalveoverridestheseptum.Withever-greaterdegreesofoverriding,
andincreasingconnectionoftheleafletsofthepulmonaryvalvewithintheright
ventricle,thespectrumofanomaliesculminatesindoubleoutletfromtheright
ventriclewithsubpulmonaryinterventricularcommunication.Thiswholeseries
isoftencalledtheTaussig-Bingcomplex.Wedividetheseriesatitsmidpoint,
includingonlythosewithlessthanhalfthecircumferenceoftheoverriding
pulmonaryvalveconnectedwithintherightventricleasexamplesof
transposition.Equallysignificantfromthesurgicalstandpointarethosedefects
thatextendtoopentotheinletoftherightventricle.Thesearehiddenbeneath
theseptalleafletofthetricuspidvalve,complicatingtheirsurgicalrepair.When
thedefectextendstoopenintotherightventricularinlet,thereisthepotential
forstraddlingandoverridingofthetricuspidvalve.Inthissetting,themuscular
ventricularseptumnolongerextendstothecrux,andtheatrioventricular
conductionaxistakesoriginfromananomalousposteroinferioratrioventricular
node.Apartfrominthepresenceofoverridingofthetricuspidvalve,the
conductiontissueiscarriedontheleftventricularaspectoftheseptum,andthe
posterocaudalrimofthedefectismostvulnerableduringsurgicalcorrection.As
withisolateddefects,theconductionaxisisbetterprotectedwhentheposterior
limboftheseptomarginaltrabeculationfuseswiththeventriculoinfundibular
fold(Fig.37.7A).However,ifamusculardefectopenstotheinlet,theaxisof
conductiontissuewillbefoundinanterocephaladposition.Therecanbeother
typesofdefects,suchasmultiplemusculardefects,solitaryapicalmuscular
defects,ordoublycommitteddefectsroofedbytheconjoinedleafletsofthe
aorticandpulmonaryvalves.Theyarelesscommon.Theaortaisalsorarely
foundposteriorlyandtotherightinthepresenceofaventricularseptaldefect.
Withthisarrangement,thereisusuallyaortic-mitralvalvarcontinuitythrough
theroofofthedefect.Bilateralinfundibulumsarealsoseenmorefrequentlyin
associationwithadefectiveventricularseptum,mostfrequentlywhenthe
arterialtrunksaresidebyside.Otheranomaliesarealsomorefrequentin
associationwithventricularseptaldefect,includingjuxtapositionoftheatrial
appendages,aorticstenosis,andaorticcoarctation.
ObstructionoftheLeftVentricularOutflowTract
Anylesionsthatproduceobstructiontotheoutflowtractofthemorphologically
leftventricle,andwhichinthenormalheartproduceaorticobstruction,will
producesubpulmonaryobstructioninthesettingoftransposition.15Suchlesions
canbefoundatthevalvarorsubvalvarlevel(Fig.37.8).
FIG.37.8 Substratesproducingsubpulmonarystenosisintransposition.
Thelesionsarethesameasthosethatproducesubaorticstenosiswhen
theventriculoarterialconnectionsareconcordant.
Isolatedvalvarobstructionisrare,beingmorecommonincombinationwith
subvalvarobstruction,whichmaybedynamic,fixed,orboth.Dynamic
obstructionisproducedbybulgingoftheventricularseptum.Initsmostsevere
form,thisisreminiscentofhypertrophicobstructivecardiomyopathy.When
septalbulgingitselfislesssevere,obstructionoftheleftventricularoutflowtract
isfrequentlyexacerbatedbyafibrousridgelocatedontheseptalbulge.Thiscan
progresstoformacompletesubvalvarshelf,theridgeextendingontothefacing
surfaceofthemitralvalvarleaflet.Theextentoffibrousstenosiscanalsobe
moreelongated,givingatunnellesion.Otherrarerformsofstenosisare
producedbyanomalousattachmentofthetensionapparatusofthemitralvalve
acrosstheoutflowtractorbyaneurysmsoffibroustissuetagsbulgingintothe
outflowtract.Allcanexistwithanintactventricularseptumorinassociation
withaventricularseptaldefect.However,whenthereisaseptaldefect,thereis
anothermostsignificanttypeofstenosis,namelyamalalignmentanddeviation
ofthemuscularoutletseptumintotheleftventricle.Thiscombinationnarrows
thesubpulmonaryoutflowtractinassociationwithoverridingoftheaorticvalve
(Fig.37.7B).Mostofthesefixedstenosespresentmajorproblemsinsurgical
removal,eitherbecauseoftheirownintrinsicmorphology(e.g.,apapillary
