Andersons pediatric cardiology 57
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isomerism,thegreatvesselsusuallylietothesamesideofthespine,withthe
cavalveininanteriorpositioninthosewithisomerismoftherightatrial
appendages,andposterior,orwiththeazygosveinposterior,inthosehaving
isomerismoftherightatrialappendages.
Ingeneral,isomerismoftherightatrialappendagesisassociatedwithabsence
ofthespleen,whereasisomerismoftheleftatrialappendagesisassociatedwith
multiplespleens.Patientswithisomerismoftheatrialappendagesthereforeare
frequentlygroupedtogether,fromthecardiacstandpoint,underthebannerofthe
“splenicsyndromes.”Thisapproachismuchlessaccuratethandescribingthe
syndromesdirectlyintermsofisomerismoftheatrialappendagesbecausethe
correlationbetweenisomerismoftherightatrialappendagesandabsenceofthe
spleen,andbetweenisomerismoftheleftatrialappendagesandmultiple
spleens,isfarfromperfect.20
AtrioventricularJunctions
Inthenormalheart,theatrialmyocardiumiscontiguouswiththeventricular
massaroundtheorificesofthemitralandtricuspidvalves.Electricalinsulation
isprovidedatthesejunctionsbythefibrofattyatrioventriculargrooves,other
thanatthesiteofthepenetrationofthebundleofHis.Toanalyzeaccuratelythe
morphologyoftheatrioventricularjunctionsinabnormalhearts,itisnecessary
toknowtheatrialarrangement.Equally,itisnecessarytoknowthemorphology
oftheventricularmasstoestablishwhichatriumisconnectedtowhichventricle.
Withthisinformationathand,itispossibletodefinethespecificpatternsof
unionornonunionacrossthejunctionsandtodeterminethemorphologyofthe
valvesguardingtheatrioventricularjunctions.Inheartswithcomplex
malformations,itisalsonecessaryonoccasiontodescribetheprecisetopology
oftheventricularmassandtospecifytherelationshipsoftheventricles
themselves.
PatternsofUnionorNonunionofthe
AtrialandVentricularChambers
Asalreadydescribed,thepatternsdependonthewaythatthemyocardiumof
bothatriumsisjoinedtotheventricularmyocardiumaroundtheentiretyofthe
atrioventricularjunctions,theatrialandventricularmusclemassesbeing
separatedfromtheelectricalstandpointbytheinsulatingfibrofattytissuesofthe
junctionsotherthanatthesiteoftheatrioventricularbundle.Thecavitiesofthe
atrialchambersthereforearepotentiallyconnectedtotheunderlyingventricular
cavitiesviatheatrioventricularorifices.Ineveryheart,becausetherearealways
twoatrialchambers,thereisthepossibilityfortwoatrioventricularconnections,
whichwillberightsidedandleftsided(Fig.1.11).
FIG.1.11 Four-chambersectionofthenormalheartshowingthepaired
atrioventricularjunctions(arrows)acrosswhichthecavitiesoftheatrial
chambersareconnectedtotheirappropriateventricles.
Thisisthecaseirrespectiveofwhetherthejunctionsthemselvesareguarded
bytwovalves(seeFig.1.11)oracommonvalve(Fig.1.12).
