Andersons pediatric cardiology 682
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concernedandtheatrialappendages,therightandleftsidesaremirror
imagesofeachother(enantiomeric).Thisistheessenceofbodily
isomerism.Thequestionmarksrefertothefactthatorganarrangementin
thebellyhasnorealpatternwitheitherleftorrightisomerism.
VenoatrialConnections
Anomalousvenoatrialconnectionsaretheruleinpatientswithisomericatrial
appendages.Asalreadyemphasized,somepatientswithisomericatrial
appendagescanhaveanoverallpatternofvenousdrainagethatcanbe
consideredusual(Figs.26.8and26.9),ormirrorimaged(Figs.26.10and26.11).
Eveninthesepatients,however,thevenoatrialconnectionscanneverbe
anatomicallynormalwhentheappendagesareisomeric.Ineachindividual
thereforeanypatternmustbeanticipated.Certainfeaturesaresufficiently
common,nonetheless,usuallytopermitthedifferentiationofrightandleft
isomerism.Itistheconnectionofthepulmonaryveinsthatismostreliablein
permittingthisdistinction.Inrightisomerism,becausethepectinatemuscles
extendtothecruxonbothsides,thepulmonaryvenousconnectionsarealways
anatomicallyabnormal.Thus,whenallthepulmonaryveinsconnecttooneof
themorphologicallyrightatrialchambers,bethechamberright-orleft-sided,
theanatomyisalwaysabnormalwhencomparedtothenormalconnectionsof
thepulmonaryveinstothemorphologicallyleftatrium.Thisisbecausethe
morphologicallyleftatriumneverexhibitspectinatemusclesextendingtothe
crux,asisthecasewhenbothappendagesaremorphologicallyright.Inthe
minorityofcasesinwhichthepulmonaryveinsconnectdirectlytoanatrium
withamorphologicallyrightappendage,theyjointheatrialchamberposteriorly
(Fig.26.12).Mostusually,whenthepulmonaryveinsdoreturndirectlytothe
heartinthesettingofrightisomerism,theymaketheirconnectionviaafibrous
confluence,typicallyopeningcentrally.Thereforewhenthereare
morphologicallyrightappendagesbilaterally,theconnectionsofthepulmonary
veinswillalwaysbeanomalousanatomically,eveniftheatriumreceivingthe
veinsisitselfleft-sided.Inabouthalfthepatientshavingisomericright
appendages,suchsemanticpitfallsdonotarise.Thisisbecausethepulmonary
veinsdrainexclusivelytoanextracardiacsource.Thesiteofanomalous
connectionisasvariedaswhentotallyanomalouspulmonaryvenousconnection
isseenwithusualatrialarrangement(seeChapter29).Theproblemsof
obstructionwithintheanomalouspulmonaryvenouspathwayarethesame.
Indeed,clinicalexperiencesuggeststhatanobstructedsupracardiacpathwayis
morefrequentinthesettingofrightisomerismthaninusualarrangement.The
otheruniversallyconstantfeatureofthevenoatrialconnectionsinthepresence
ofisomericrightatrialappendagesisabsenceofthecoronarysinus(Fig.26.13),
thischannelbeingacomponentofthemorphologicallyleftatrioventricular
junction.Whenthepectinatemusclesextendbilaterallytothecrux,thereisno
roomtoenclosethesinuswithinthejunctions.Somepatientswithabsenceofthe
spleenmaypossessacoronarysinus,butthisisbecausenotallpatientswith
“asplenia”haveisomericrightatrialappendages.
FIG.26.8 Heartwithisomerismoftheleftatrialappendages
demonstratingquasi-usualvenousrelationships.(A)Thebaseoftheheart
showsbilateraltubularappendagesandtheirnarrowjunctions(redarrows)
withtheatrialvestibule.Thereisaright-sidedsuperiorcavalveinwitha
largeazygosveinindicativeofazygoscontinuationoftheinferiorcaval
vein.Thepulmonaryveinsdraintotheleft-sidedatrium(whiteboxand
arrows).(B)Theposteroinferiorviewofthesameheart.Thesuperiorcaval
veinismarkedwithablackstarandtherightandleftpulmonaryveinswith
redstars.(C)Short-axisviewofthesameheartdemonstratingso-called
noncompactionofbothventriclesandtheinterventricularseptum.There
wasalsotransposition.
FIG.26.9 Heartwithisomerismoftherightatrialappendagesand
tricuspidatresiademonstratingquasi-usualvenousrelationships.Pectinate
musclesextendtothecruxonboththeright(A)andleftsides(B).InA,the
superiorandinferiorcavalveinsdraintotheright-sidedatrium;inB,the
pulmonaryveinsdraintotheleft-sidedatrium.Notethelargeatrialseptal
defect.AV,Atrioventricular.
