Andersons pediatric cardiology 772
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defect,whichisanatrioventricularseptaldefectwithacommonatrioventricular
junction.ThislesionisdescribedfurtherinChapter32.Therefore
maldevelopmentoftheprimaryatrialseptumitself,afterithasfusedwiththe
ventricularseptumandtheendocardialcushions,resultsindefectswithinthe
ovalfossa.Thiscanbedueeithertodeficiencyofitssuperioredge,sothatitno
longeroverlapstheinfoldedsuperiorrim,ortobreakdownoftheseptumtoa
greaterorlesserdegree,resultinginthevarioustypesofperforateorfenestrated
defectswithinthefossa(seeFig.29.5).Inthemostseveredefects,themuscular
rimalsobecomeseffaced.Itispossibletoenvisagetemporaryeffacementofthe
rimoftheovalfossa,sincethisisnomorethanamuscularinfolding.Such
effacementinthepresenceofvolumeload,withsubsequentrestorationofthe
foldoncethevolumeloadhasbeencorrected,isalikelyexplanationfor
spontaneousclosureofsomedefectswithintheovalfossaduringtheneonatal
period.Sinusvenosusdefectsareexplainedonthebasisofanomalous
connectionoftherightpulmonaryveinstoasystemicvenouschannel,withthe
pulmonaryveinsretainingtheirleftatrialconnections(seeFig.29.10).The
coronarysinusdefectisexplainedonthebasisofresorptionofthedualwalls
thatusuallyseparatethelumenofthecoronarysinusitselffromthecavityofthe
leftatrium(seeFig.29.11).Therarevestibulardefect(seeFig.29.7)isdueto
improperfusionormuscularizationofthecomponentsformingtheanteroinferior
buttressoftheatrialseptum;thisprocessinvolvesboththevestibularspineand
themesenchymalcapcarriedontheleadingedgeoftheatrialseptum.
AssociatedAnomalies
Cardiac
Almostanycardiacdiseasecanbeassociatedwithaninteratrialcommunication,
andforsomeitspresenceiscrucialtosurvival(e.g.,totallyanomalous
pulmonaryvenousconnection,absentleftandrightatrioventricular
connections).Partiallyanomalousconnectionofthepulmonaryveinsisa
relativelycommonassociatedfindinginpatientswithinteratrial
communications.Indeed,itisthephenotypicfeatureofthesinusvenosus
variety.Anovalfossadefectcommonlyoccursinadditiontotheprimumdefect
whenthereisanatrioventricularseptaldefect,withthemostextensiveinstances
(leadingtoalmostcompleteabsenceofatrialseptation)occurringwhenthereis
isomerismoftheatrialappendages.
Noncardiac
TheassociationofDownsyndromewithostiumprimumdefectsiswellknown.
TheincidenceofDownsyndromehasbeenonly2.9%inthosehavingsurgery
fordefectsintheovalfossa.TheskeletalanomaliesofHolt-Oramsyndrome12
andelectrophysiologicabnormalitiesareexamplesofnoncardiacanomalies,
whichoccurinafewpatients.Familialdefectsarewellreported,with
transmissionratesof40%to100%,suggestingautosomaldominantinheritance.
Indeed,ifmorethantwofamilymembersareaffected,geneticevaluationwould
bewarrantedandthescreeningofotherfamilymembersandfirst-degree
relativessuggested.13Aswithassociatedcardiacmalformations,noncardiac
anomaliesarerelativelyrareinpatientswithanatrialseptaldefect.
Pathophysiology
Thepathophysiologyofinteratrialcommunicationsdependsontheunderlying
andassociateddiseases,theresultinghemodynamics,andthesizeofthedefect.
Inisolatedovalfossadefectsthereisusuallyasubstantialleft-to-rightshunt,
resultinginahighratioofpulmonary-to-systemicflow.Underthese
circumstancestheprimarydeterminantsoftheamountofshuntingarethesizeof
thedefectandtherelativeresistancetoinflow,orthecomplianceofthe
ventricles.Aswithaventricularseptaldefect,thesiteofthedefectintheatrial
septumdoesnotinfluencethemagnitudeofflowacrossit,althoughrelative
contributionstotheshuntfromtheindividualpulmonaryveinsmayvary
dependingonthelocationofthedefect.
EffectofSizeoftheDefect
Mostisolatedinteratrialcommunicationsthatarerecognizedclinicallyare
essentiallynonrestrictive,andflowacrossthemwilldependonverysubtle
pressuretransientsbetweentheatria,generated,atleastinpart,bythefunction
oftheventricles.Atbirth,rightandleftventricularcomplianceisapproximately
equal,andthereislittleshuntingacrossanatrialdefectineitherdirection.
Pulmonaryvascularresistanceandpressuregenerallyundergotheirnormal
dramaticfalloverthefirstdaysoflifeinpatientswithaninteratrial
communication,andrightventricularhypertrophyregresses.Hypertrophyperse
doesnotworsencompliance,butthenormalresponsetoavolumeloadisforthe
atriumandventricletodilateprogressively,andthisisthenormnomatterwhat
thetypeofinteratrialcommunication.Progressivedilationmaybesubclinical
foryears,andthepulmonaryvascularresistancestayslowinchildhoodand
earlyadultlife,butpatientsaresusceptibletoanincreaseinresistanceifthe
flowofbloodtothelungsremainshighfordecades.3,14,15Iftherightventricle
fails,Eisenmengersyndromemayresult,withreversaloftheatrialshunttoa
predominantright-to-leftpattern.Aright-to-leftatrialshuntmayalsobe
promotedbytricuspidstenosisorseveretricuspidvalvarregurgitation.
Insomecasestheinteratrialcommunicationmayresultfromincompetenceof
thevalveoftheovalforamenratherthanfromatruedeficiencyoftheatrial
septum.Thisincompetencecanleadtoconsiderableleft-to-rightshunting(even
ifthedefectissmall)whenthereareassociatedabnormalitiesthatleadto
