Andersons pediatric cardiology 786
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FIG.30.1 Heartwithdivisionoftheleftatrium,photographedfromtheleft
side.Thepartitiondividesthechamberintoapulmonaryvenous
component,whichcontainstheleftatrialaspectoftheovalfossaanda
vestibularcomponent,whichincludestheleftatrialappendage.
Evenifthecharacteristicfeatureistheobliquityofthedividingpartition,
thereisstillconsiderableanatomicvariability.Thesignificantvariationsarethe
sizeofthecommunicationbetweenthepulmonaryvenousandvestibular
compartments,andthesiteofaninteratrialcommunication,ifpresent.Other
malformationscancoexist.Itisrareforthecommunicationbetweenthe
compartmentstobenonrestrictivebythetimeitisdiscovered.Inmostexamples
gainingclinicalattention,theareaofthecommunicationissignificantlysmaller
thantheareaofthemitralvalve,anditissometimesbarelymorethanapinhole
(Fig.30.2).Thecommunicationisusuallysingle,butmultipleconnectionsare
sometimesseen.Theatrialseptumisintactinuptohalfofpatients.When
present,aseptaldefectisalmostalwayswithintheovalfossa,communicating
mostfrequentlywiththepulmonaryvenouscompartment(seeFig.30.2).On
occasion,theovalfossacanbeincommunicationwiththevestibularcomponent.
Inrarecases,thecommunicationwiththevestibularchambercanbean
atrioventricularratherthananatrialseptaldefect.6Althoughsomeofthe
pulmonaryveinsusuallyconnecttothedividedatrium,justifyingdescriptionof
thepulmonaryvenouscompartment,variouspartiallyanomalousvenous
connectionshavebeendescribed.Theanomalouspulmonaryvenous
connections,iftheyexist,arebestaccountedforindescriptivefashionalong
withotherrareassociatedmalformations,suchasmitralatresiaordiscordant
atrioventricularconnections.
FIG.30.2 HeartshowninFig.30.1reconstitutedandsectionedto
replicatetheechocardiographicfour-chamberview.Notetheoblique
dividingshelf,withonlyapinholemeatusbetweenthetwocomponentsof
thedividedleftatrium.Notealsothattheovalfossaopenstothe
pulmonaryvenouscomponent.
Thecharacteristicdividingpartitionisadoublelayerofmyocardium,which
hasbeeninterpretedtoprovideacluetothemorphogenesisofthelesion.7The
rightsideoftheheartisusuallyconsiderablyhypertrophiedbecauseof
associatedpulmonaryhypertension.Aswithothercasesofobstructedpulmonary
venousreturn,therearealsomarkedchangeswithinthelungsandthepleural
lymphatics.Intermsofmorphogenesis,thelesionwasinitiallyexplainedonthe
basisoffailureofabsorptionofthecommonpulmonaryveinintotheleftatrium.
This“malincorporation”hypothesiswasreplacedbythe“entrapment”concept,7
whichaccountswellfortheclassicanomalybutlessreadilyexplainsthevariant
inwhichtheovalfossaisincommunicationwiththevestibularchamber.At
present,boththeoriesremainspeculative.
IncidenceandEtiology
Onlyfourexamplesofdividedleftatriumwerefoundinnearly4000
catheterizationsperformedinpatientswithcongenitallymalformedheartsatthe
RoyalBromptonHospitalfrom1970through1982.8Malesareaffectedmore
frequentlythanfemales.Ithasbeensuggestedthatthepartitioncouldbeinduced
duringdevelopmentbypersistenceoftheleftsuperiorcavalvein,9butthisdoes
notfitwiththefactthatsofewpatientswithpersistentleftcavalveinsalsohave
dividedleftatriums.
PresentationandClinicalFeatures
Theageandmodeofpresentationrelatetothesizeofthecommunication
betweenthepulmonaryvenousandvestibularchambers.Presentationwith
symptomsusuallyimpliesasmallcommunication,butsymptomswillbe
amplifiedinthepresenceofaleft-to-rightshunt,forexampleapatentarterial
duct.Patientsusuallypresentininfancyorearlychildhoodwithdyspneaand
frequentrespiratoryinfections,althoughpresentationinadultlifewith
congestiveheartfailure,unexplainedpulmonaryhypertension,andhemoptysisis
welldescribed.Whenpresent,cyanosisisusuallytheconsequenceofaright-toleftshuntfromtherightatriumthroughanovalforamenoratrialseptaldefectto
thevestibularcompartmentofthedividedleftatrium.Theclinicalsignsare
dominatedbyevidenceofpulmonaryvenouscongestionandpulmonary
hypertension.Thechildwithsevereobstructionwillbepaleandsweating,with
tachycardiaandextremebreathlessnessonfeeding,butusuallywillremainfully
saturated.Theremaybearightventricularheaveand,onauscultation,the
pulmonarycomponentofthesecondsoundisalmostalwaysaccentuated.No
murmursmaybeheard,althoughanapicaldiastolicmurmurmaysimulatemitral
stenosis.Asoft,blowingsystolicmurmurmayreflectsecondarytricuspid
regurgitation.Occasionallytheapicalmurmuriscontinuous,ortheearly
diastolicmurmurofpulmonaryincompetencemaybeheardsecondaryto
pulmonaryhypertension.Thesignsofcongestiveheartfailurearefoundwhen
thissupervenes,includingcracklesinthelungsandanenlargedliver.
Investigations
Thechestradiographusuallyrevealscardiomegalyandshowsthepresenceof
