Andersons pediatric cardiology 845
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differentplanethanthemuscularinterventricularseptumaswellasthefact
thatthisplaneremainsnearthecommissurebetweentheanterosuperior
andseptalleafletsofthetricuspidvalve,itcanbeappreciatedthatthis
representstheperimembranousor“central”regionrelatedtotheright
ventricle.(C)Thesubcostalshort-axisplanedemonstratestheventricular
septaldefectlocatedadjacenttothecommissurebetweenthe
anterosuperior(A)andseptal(S)leafletsofthetricuspidvalve(asterisk),
againwithfibrouscontinuitybetweentheaorticandtricuspidvalves,with
noextensionundertheseptalleaflet(S).LA,Leftatrium;LV,leftventricle;
PV,pulmonaryvalve;RA,rightatrium;RV,rightventricle.
Perimembranousdefectsextendingtotheinletoftherightventricle,which
willadditionallydemonstratefibrouscontinuitybetweentheleafletsofthe
tricuspidandmitralvalves,arerecognizedbycutsthroughtheventricularinlets
(seeFig.32.4;Videos32.3and32.4).Thefour-chambersectionswill
demonstratethecontinuitybetweentheleafletsoftheatrioventricularvalves
withlossoftheusualoffsettingofthehingepointsoftheleaflets.Thedefect
itselfresidesimmediatelyinferiortotheseptalleafletofthetricuspidvalve(see
Fig.32.4AandVideo32.3).Ifpresent,malalignmentbetweentheatrialand
muscularventricularseptawithstraddlingandoverrideofthetricuspidvalvecan
additionallybeappreciatedinthisplane(Fig.32.21;Video32.5).Agentlesweep
ofthetransducerfromafour-chambertothree-chambercutwilldemonstratethe
fibrouscontinuityoftheleafletsofthetricuspidandaorticvalvesthroughthe
centralfibrousbody(Video32.6).Itisacommonmisconceptionthatthisview
demonstratesoutletextension.Inreality,thisplanecontinuestoinsonatethe
centralregionoftheventricularbase(compareFig.32.20BtoFig.32.20A).The
subcostalshort-axissection,withthetricuspidvalveviewedfaceon,will
demonstratethedefectextendingfromtheperimembranousregionsoastoopen
totheinletoftherightventricle(seeFig.32.4B,Fig.32.21D,andVideo32.4).
Inletmusculardefectscangivetheappearanceofbeingjuxtatricuspidwhenthey
areveryclosetotheattachmentofthetricupsidvalvetotheseptum,withonlya
smallrimofmuscularseptuminterposedbetweenthevalvarhingeandthe
defect.Iftrulymuscular,however,theywillnotextendtotheperimembranous
region(Fig.32.22;Videos32.7and32.8).
FIG.32.21 Normalheartviewedintheapicalfour-chamberplane(A)
comparedwithahearthavingtheperimembranousventricularseptal
defect(VSD)withinletextensionandmalalignmentbetweentheatrialand
muscularventricularsepta(B),whicharehighlightedinredandblue,
respectively.PanelBdemonstratesthelossofnormaloffsetbetweenthe
atrioventricularvalves(double-headedarrow)aswellasstraddlingand
overrideofthetricuspidvalvewithattachmentoftheseptalleaflettotheleft
ventricularaspectoftheinterventricularseptum.Theleftventricle(LV)is
dilated.(C)Thesubcostallong-axisplanedemonstratesfibrouscontinuity
betweentheaorticvalve(AoV)andseptalleafletofthetricuspidvalve(S),
againwithstraddlingandoverridethroughtheventricularseptaldefect.(D)
Thesubcostalshort-axisplanedemonstratestheventricularseptaldefect
extendingfromtheperimembranousregion,wherethereisfibrous
continuitybetweentheaorticvalve(AoV)andtricuspidvalveatits
commissure(asterisk)betweentheseptal(S)andanterosuperior(A)
leaflets,inferiorlyandposteriorlyalongtheseptalleafletintotheinletwhen
relatedtotherightventricle.Thetricuspidvalveoverridedoesnotappear
assignificantasintheotherviews.LA,Leftatrium;RA,rightatrium;RV,
rightventricle.
FIG.32.22 Echocardiographicimagesdemonstratingthemuscularinlet
ventricularseptaldefect(VSD).Theapicalfour-chamberplane
demonstratestheventricularseptaldefectbelowtheatrioventricularvalves,
with,however,musculartissueinterposedbetweenthedefectandthe
valves.Theatrioventricularvalveshaveretainedtheirnormaloffset
(double-headedarrow).Thesubcostalshort-axisplanedemonstratesthe
ventricularseptaldefectadjacenttotheseptalleafletofthetricuspidvalve
(S),which,however,unliketheperimembranousinletdefect(compareto
Fig.32.4),doesnotextendtotheperimembranousregionnearthe
commissure(asterisk)oftheanterosuperior(A)andseptal(S)leafletsof
thetricuspidvalveinthismuscularinletdefect.AoV,Aorticvalve;LA,left
atrium;LV,leftventricle;RA,rightatrium;RV,rightventricle.
Perimembranousdefectsopeningtotheoutletoftherightventricleareeasily
identifiedinthesubcostalrightobliquesection.Themuscularoutletseptumis
recognizableinthissettingasanintracardiacstructureformingtheentranceto
thesubpulmonaryinfundibulumandcanbemalalignedineitherthecranialor
caudaldirection(Fig.32.23).Theparasternalshort-axiscutatthelevelofthe
