Andersons pediatric cardiology 1805

morphogenesisofthelesionsmakingupthegroupofheartswith
univentricularatrioventricularconnection.

Keywords
double-inletventricle,absentatrioventricularconnection,Hypoplasticleft
heartsyndrome;pulmonaryatresiawithintactventricularseptum
morphogenesis


Introduction
Fortheanatomistandpathologist,theterms“univentricular”and“single”have
proventobeamongthemostcontroversialwordsusedtodescribeacongenitally
malformedheart.Sincethemid-1990s,lighthasbeguntoemergeattheendof
thetunnelforthoseseekingalogicalframeworkfortheuseofthesewords.Inno
smallway,thisreflectstherecognitionbycliniciansthatitisfrequentlynot
possiblesurgicallytocreateabiventricularcirculationinapatienthavingtwo
well-formedventricles.Inthesecircumstances,conversiontotheFontan
circulationpermitsboththesystemicandpulmonarycirculationstobesupported
byonlyoneoftheventricles.Inothercircumstances,aswhenthereisadoubleoutletventriclewithremoteinterventricularcommunication,itisthecombined
ventricularmassthatejectstothesystemiccirculation.Thesefactsunderscore
thegroupingofthemarkedlyheterogeneousanatomicentitiesdiscussedinthis
chapter.Thearrangementinthesettingofdouble-outletventriclesisdiscussedin
Chapter39.Theanatomyinvolvedwhenbothcirculationsaresupportedbyonly
oneventriclebecomeseasiertounderstandinconsiderationoftheextensive
controversiesintheearlierliterature,whichhasofferednumerousillogical
definitionsof“singleventricles”or“univentricularhearts.”Thesedefinitions
reflectedtheinterpretationofventricularmorphologyinpatientshavingdoubleinletventriclesasopposedtoatrioventricularvalvaratresia.1,2Itwas,ofcourse,
patientshavingtricuspidatresiawhowerefirstconvertedtotheFontan
circulation.Themajorityofpatientsnowtreatedinthisfashion,however,have
hypoplasticleftheartsyndrome.Suchpatientshaveunequivocallybiventricular
hearts,asdomanyofthosewithpulmonaryatresiaandanintactventricular

septum,whoaretreatedincomparablefashion.Hereweaddressthebasic
morphologyofalltheselesions,alongwiththosefoundinotherpatientswith
obviouslybiventricularmorphologicarrangements.Webegin,however,by
explainingwhythetopichasprovedsocontroversialforbothmorphologistsand
clinicians,whileacceptingthatsuchconsiderationsarenowlargelyofhistorical
interest.


PhilosophicalConsiderationsRelativeto
Nomenclature
Itisveryunusualtofindheartswithasolitarychamberwithintheventricular
mass.Whenfound,theyexhibitadoubleinlettoaventriclethathasparticularly
coarseapicaltrabeculationsandinwhichtheonlyseptalstructurepresentisthe
muscularoutletchamber(Fig.69.1).Suchheartshavenotonlyauniventricular
arrangementoftheventricularmassbutalsoauniventriculararrangementofthe
atrioventricularjunctions.Thisisbecause,inthesettingofallvariantsofdoubleinletventricle,theatrialchambersconnecttoonlyoneventricleirrespectiveof
whetherornottheventricularmassisitselfuniventricular.Thisfactis
significantbecause,subsequenttoastudythatappearedin1964,1itcametobe
acceptedthatthecriterionforthedefinitionofa“singleventricle”wasthe
presenceofadouble-inletatrioventricularconnection.Thiswasaccepteddespite
thefactthatthosepromotingthisterminologyrecognizedthat,inthemajorityof
thepatientshavingdouble-inletventricle,asecondchamberwaspresentwithin
theventricularmass(Fig.69.2).2Atthetime,suchheartswereconsideredtobe
“univentricular”becausethesecondchamberwasinterpretedasrepresentingan
“infundibularoutletchamber,”andhencenota“true”ventricle.Therewasa
problemwiththisapproach,sinceatthattimetheheartswithatrioventricular
valvaratresiaweredeemedtobebiventricular,withthesmallchamberin
patientshavingtricuspidatresiaacceptedasbeingarightventricle.When
comparisonsaremadebetweenthemorphologyofthesmallchamberinhearts
withtricuspidatresiaandthosewithdouble-inletleftventricle—providedthat

thecomparisonismadeinthesettingofheartshavingthesameventriculoarterial
connections—thechambersarevirtuallyindistinguishable(Fig.69.3).3Such
similarityisnomorethanshouldbeexpected,sinceinbothtricuspidatresiaand
double-inletleftventriclethelargerventricleisofleftventricularmorphology.
Thesmallerchamberisanincompleterightventriclelackingitsinletcomponent.
Indouble-inletleftventricle,thisoccursbecausebothatrioventricularjunctions
aresupportedbythedominantventricle(seeFig.69.2).Inclassictricuspid
atresia,incontrast,therightventriclelacksitsinletbecausethereiscongenital
absenceoftherightatrioventricularconnection(Fig.69.4).Inbothsettings,asin
theheartswithanindeterminateventricle,itistheatrioventricularconnections
thatareuniventricular.Withonesmallexception,therefore,itfollowsthatall