Andersons pediatric cardiology 61
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potentialasopposedtoanabsentatrioventricularconnection.Acommonvalve
guardsbothright-andleft-sidedatrioventricularjunctions,irrespectiveofits
morphology.Avalvestraddleswhenitstensionapparatusisattachedtoboth
sidesofaseptumwithintheventricularmass.Itoverrideswhenthe
atrioventricularjunctionisconnectedtoventriclesonbothsidesofaseptal
structure.Aright-sidedvalve,aleft-sidedvalve,oracommonvalvecan
straddle,canoverride,orcanstraddleandoverride.Veryrarely,bothright-and
left-sidedvalvesmaystraddleand/oroverrideinthesameheart.
Whenoneatrioventricularconnectionisabsent,thepossiblemodesof
connectionaregreatlyreduced.Thisisbecausethereisasolitaryright-orleftsidedatrioventricularconnectionandhenceasolitaryatrioventricularvalve.The
singlevalveisusuallycommittedinitsentiretytooneventricle.Morerarely,it
maystraddle,override,orstraddleandoverride.Theselatterpatternsproduce
theextremelyraregroupofuniatrialbutbiventricularconnections(Fig.1.20).
FIG.1.20 Tricuspidatresiaduetoabsenceoftherightatrioventricular
connectionassociatedwithstraddlingandoverridingoftheleft
atrioventricularvalve.Thisproducesanatrioventricularconnectionthatis
uniatrialbutbiventricular.Theconnectioncanbefoundwithany
combinationofatrialarrangementandventriculartopology.
Avalvethatoverrideshasanadditionalinfluenceondescription.Thisis
becausethedegreeofcommitmentoftheoverridingatrioventricularjunctionto
theventriclesoneithersideoftheseptumdeterminestheprecisefashionin
whichtheatriumsandventriclesarejoinedtogether.Heartswithtwovalves,in
whichonevalveisoverriding,areanatomicallyintermediatebetweenthosewith,
ontheonehand,biventricularand,ontheotherhand,univentricular
atrioventricularconnections.Therearetwowaysofdescribingsuchhearts.One
istoconsidertheheartsasrepresentingaspecialtypeofatrioventricular
connection.Thealternativeistorecognizetheintermediatenatureofsuchhearts
inaseriesofanomalies,andtosplittheseriesdependingontheprecise
connectionoftheoverridingjunction.Forthepurposesofcategorization,only
thetwoendsoftheseriesarelabeled,withheartsinthemiddlebeingassignedto
oneorotheroftheendpoints.Wepreferthissecondoption(seeFig.1.19).
Whenmostofanoverridingjunctionisconnectedtoaventriclethatisalso
joinedtotheotheratrium,wedesignatethepatternasbeingdoubleinlet.Ifthe
overridingjunctionisconnectedmostlytoaventriclenotitselfjoinedtothe
otheratrium,eachatriumiscategorizedasthoughjoinedtoitsownventricle,
givingthepossibilityofconcordant,discordant,ormixedconnections.
Whendescribingatrioventricularvalves,itshouldalsobenotedthatthe
adjectives“mitral”and“tricuspid”arestrictlyaccurateonlyinheartswith
biventricularatrioventricularconnectionshavingseparatejunctions,each
guardedbyitsownvalve.Inthiscontext,thetricuspidvalveisalwaysfoundin
themorphologicallyrightventricleandthemitralvalveinthemorphologically
leftventricle.Incontrast,inheartswithbiventricularatrioventricular
connectionsbutwithacommonjunction,itisincorrecttoconsiderthecommon
valveashavingmitralandtricuspidcomponents,evenwhenitisdividedinto
rightandleftcomponents.Theseright-andleft-sidedcomponents,particularly
ontheleftside,bearscantresemblancetothenormalatrioventricularvalves(see
Chapter36).Inheartswithdoubleinlet,thetwovalvesareagainbetter
consideredasright-andleft-sidedvalvesratherthanasmitralortricuspid.
Similarly,althoughitisusuallypossible,whenoneconnectionisabsent,to
deducethepresumednatureoftheremainingsolitaryvalvefromconceptsof
morphogenesis,thisisnotalwayspracticalorhelpful.Thevalvecanalways
accuratelybedescribedasbeingrightorleftsided.Potentiallycontentious
argumentsarethusdefusedwhentheright-orleft-sidedvalvestraddlesinthe
absenceoftheotheratrioventricularconnection,givingtheuniatrialbut
biventricularconnections.
VentricularTopologyandRelationships
Eveninthenormalheart,theventricularspatialrelationshipsarecomplex.The
inletportionsaremoreorlesstotherightandleft,withtheinferiorpartofthe
muscularventricularseptumlyinginanapproximatelysagittalplane.Theoutlet
portionsaremoreorlessanteroposteriorlyrelated,withtheseptumbetween
theminanapproximatelyfrontalplane.Theapicalportionsextendbetween
thesetwocomponents,withthemuscularseptumspiralingbetweentheinletand
outletcomponents.Ashorthandtermisneededtodescribesuchcomplexspatial
arrangements,andweusetheconceptofventriculartopology(seeFig.1.5).In
personswithusuallyarrangedatriumsanddiscordantatrioventricular
connections,theventricularmassalmostalwaysshowsaleft-handedtopologic
pattern,whereasright-handedventriculartopologyisusuallyfoundwiththe
combinationofmirror-imagedatriumsanddiscordantatrioventricular
connections.Althoughthesecombinationsarealmostalwayspresent,exceptions
canoccur.Whennotingsuchunexpectedventricularrelationshipsasafeature
independentofthetopology,weaccountforright-left,anterior-posterior,and
superior-inferiorcoordinates.Whennecessary,wedescribethepositionofthe
threeventricularcomponentsseparatelyandrelativetoeachother.
Inheartswithdisharmoniousarrangementsinthesettingofusualatrial
arrangementanddiscordantatrioventricularconnections,thedistalpartsofthe
ventriclesareusuallyrotatedsothatthemorphologicallyrightventricular
trabecularandoutletcomponentsaretotherightoftheirmorphologicallyleft
ventricularcounterparts,givingtheimpressionof“normalrelationships.”In
such“criss-cross”heartsseenwithusualatrialarrangementandconcordant
atrioventricularconnections,theventricularrotationgivesaspuriousimpression
ofleft-handedtopology.Incaseswithextremerotation,theinletofthe
morphologicallyrightventriclemayalsoberightsidedinassociationwith
discordantatrioventricularconnections.Providedrelationshipsaredescribed
accuratelyandseparatelyfromtheconnectionsandtheventriculartopology,
noneoftheseunusualandapparentlycomplexheartswillbedifficulteitherto
diagnoseortocategorize.Inadditiontotheseproblematiccriss-crosshearts,we
havealreadydiscussedhowdescriptionofventriculartopologyisessentialwhen
accountingforthecombinationofisomericappendageswithbiventricularmixed
atrioventricularconnections.Thisisbecause,inthissituation,thesameterms
wouldappropriatelybeusedtodescribetheheartinwhichtheleft-sidedatrium
