Andersons pediatric cardiology 846
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aorticvalvewillsimilarlyshowthisdiscreteoutletseptum.Thedefectwill
extendfromtheperimembranousregionataroundthe9to11o'clockposition
andopenintotheoutletregionatapproximately12o'clock(Figs.32.24and
32.25;Videos32.9to32.11).Inthesettingofanterocranialmalalignmentofthe
outletseptum,theparasternallong-axissectionwillusuallydemonstrate
overridingoftheleafletsoftheaorticvalve.Asisthecaseinassessingthe
relationshipsofthevalvestotheunderlyingchambersinotherdefects,43
accuracyisachievedwhentheinterrogatedvalveisplacedinashort-axisplane,
withasweepmadeinferiorlyintotheventricularmass(seeFig.32.24).
Similarly,fordefectsopeningbetweentheoutletsandassociatedwith
posterocaudaldeviationoftheoutletseptum,usuallyinthesettingofaortic
coarctationorinterruption,boththeparasternallong-andshort-axissectionswill
demonstratethedeviatedoutletseptum.Inthissettingtheposterocaudal
malalignmentmaymakeextensionofthedefecttotheoutletregionlessobvious
intheshort-axisplane,asthedefectmayappeartoextendtoonlyapproximately
11o'clock(seeFig.32.25;Video32.11).
FIG.32.23 Echocardiographicimageinasubcostalrightanterioroblique
planedemonstratingaperimembranousventricularseptaldefectwithoutlet
extensionandanteriordeviationofthemuscularoutletseptum.The
muscularoutletseptumcanberecognizedasadiscretestructure,located
exclusivelyintherightventricle,separatingthesubaorticand
subpulmonaryoutflowtracts,andsupportingthefreestandingmuscular
subpulmonaryinfundibulum.Theredarrowindicatesthedefectthrough
whichtheaorticandtricuspidvalvesareindirectcontact.
FIG.32.24 Echocardiographicimagesdemonstratingthe
perimembranousventricularseptaldefect(VSD)withoutletextensionand
anteriordeviationofthemuscularoutletseptum,ortheEisenmenger
defect.(A)Theparasternallong-axisplanedemonstratestheaorta
overridingthecrestofthemuscularinterventricularseptum,withanterior
deviationofthemuscularoutletseptum(star).Theventricularseptaldefect
issmallanddifficulttoappreciateinthistwo-dimensionalimage.(B)Inthe
parasternalshort-axisplane,theventricularseptaldefectismuchlarger
andisdemonstratedtobeperimembranouswithfibrouscontinuitybetween
theseptalleafletofthetricuspidvalve(S)andtheaorticvalve(AoV).The
defectextendstotheoutletregionwithanteriordeviationofthemuscular
outletseptum(star).Thesubpulmonaryinfundibulumiswellformedwithno
subpulmonaryorpulmonaryvalve(PV)stenosis,differentiatingthisfrom
tetralogyofFallot.LA,Leftatrium;LV,leftventricle;RA,rightatrium;RV,
rightventricle.
FIG.32.25 Echocardiographicimagesdemonstratingthe
perimembranousventricularseptaldefect(VSD)withoutletextensionand
posteriordeviationofthemuscularoutletseptum.(A)Theparasternallongaxisplanedemonstratestheperimembranousventricularseptaldefectwith
posteriordeviationofthemuscularoutletseptum(star),creatingsubaortic
valve(AoV)stenosis.(B)Theparasternalshort-axisplanedemonstrates
theperimembranousventricularseptaldefectextendingfromtheseptal
leafletofthetricuspidvalve(S)towardthesubpulmonaryoutletregion.The
outletseptumisposteriorlydeviated.LA,Leftatrium;LV,leftventricle;PV,
pulmonaryvalve;RA,rightatrium;RV,rightventricle.
Aspreviouslymentioned,musculardefectsopeningtotherightventricular
inletareseeninthefour-chamberview.Theirpathognomonicfeatureisthe
presenceofmuscleinterposedbetweentheedgeofthedefectandthehingeof
theseptalleafletofthetricuspidvalve.Thismeansthatthereisretentionofthe
featureofatrioventricularvalvaroffsetting(seeFig.32.22AandVideo32.7).
Evenmore,thesubcostalshort-axisplanewillshowthat,althoughthedefect
residesinferiortotheseptalleafletofthetricuspidvalve,itdoesnotextendto
theperimembranousregion(seeFig.32.22BandVideo32.8).Largedefects
withintheapicalmuscularseptumareidentifiedinthefour-chamberandshortaxisplanes(Fig.32.26;Video32.12),whereasmusculardefectsopeningtothe
subpulmonaryoutletarebestidentifiedfromparasternalorsubcostalshort-axis
approaches.Suchdefectsarereadilydifferentiatedfromtheperimembranous
outletdefectanddoublycommitteddefect(Fig.32.27).Thecutdemonstratesthe
presenceorabsenceoffibrouscontinuitybetweentheleafletsofthetricuspid
andaorticvalves,whichinturndependsonthepresenceorabsenceofthe
posterocaudallimboftheseptomarginaltrabeculation,aswellasthe
developmentofthesubpulmonaryinfundibulumandresultingpresenceor
absenceofcontinuitybetweenthearterialvalves.Smallormultiplemuscular
