Andersons pediatric cardiology 1808

HypoplasticLeftHeartSyndrome
Ratherthanbeingasingleanatomicentity,thehypoplasticleftheartsyndrome
groupstogetherentitieswithcharacteristicphysiologicandclinicalproperties.
TheearliestgroupingwasmadebyLev,buthedescribedthesyndromeas
“hypoplasiaoftheaortictract.”8Hypoplasiaoftheleftheartisnotalwaysthe
sameasaorticatresiaorhypoplasia.Onrareoccasions,theaorticlesionscanbe
foundinthesettingofaleftventricleofnormalsize,particularlywhentheaorta
takesitsoriginfromthemorphologicallyrightventricle.ItwasNoonanand
Nadas,asfaraswecanestablish,whofirstusedtheterm“hypoplasticleftheart
syndrome.”9Althoughthecombinationsofanatomiclesionsthatconstitutethe
syndromearevariable,thefeatureswhenseentogetherareunmistakable.Thus
thesyndromeincludesthemajorityofcasesofaorticatresiaandmanyofthose
withcriticalaorticstenosis.Themitralvalvecansimilarlybestenoticoratretic.
Inallinstances,however,akeyfeatureistheintegrityoftheventricularseptum.
InmostofthecasesdescribedintheinitialinvestigationofNoonanandNadas,9
aorticcoarctationwasthemajoranatomicfeature,althoughtheleftventriclewas
deemedtobehypoplastic.Itisquestionablewhetherpatientswithsuchfindings
wouldtodaybeincludedashavinghypoplasticleftheartsyndrome.Rare
examplesarefoundinwhichthemitralandaorticvalvesareofnormal
dimensionsrelativetothecoexistinghypoplasiaoftheleftventricle.
Biventricularrepairispossibleinsuchcases,followingsimplereliefofany
obstructionwithintheaorticarchanddescendingaorta.10Thisshowsthatmajor
difficultiesremaininprovidinganall-encompassinganatomicdefinitionfor
hypoplasiaoftheleftheart.11Itismorerealistic,therefore,toanalyzethe
unifyinghemodynamicfeatures.Inphysiologicandclinicalterms,hypoplasiaof
theleftheartcanbedefinedasthesituationwherethesystemiccirculationis
dependentonthemorphologicallyrightventricleinthesettingofatresiaor
severehypoplasiaoftheaorticvalve.12Suchhypoplasiaoftheleftheartis
usuallyfoundinthesettingofusualatrialarrangementwithconcordant
ventriculoarterialconnections.Therecanbeconcordantatrioventricular
connections(Fig.69.7,left)ormitralatresiaduetoabsenceoftheleft

atrioventricularconnection(Fig.69.7,right).Inthosewithmitralatresia,theleft
ventricularcavityisoftennomorethanaslitintheposteroinferiorwallofthe
ventricularmass.Itisalmostimpossibletodetermineonmorphologicgrounds


whentheleftventricleistobeconsideredhypoplasticinpatientswithaortic
valvarstenosisratherthanatresia.Whenthereisobviousfibroelastosisinthe
smallventricleandtherightventricleisapex-forming,patientswithsuchhearts
certainlyfulfilltheanatomiccriterionsforthesyndrome(Fig.69.8).Theleft
ventricularwallsarehypertrophiedwhenthereismitralstenosisratherthan
atresia(seeFig.69.7,left).Indeed,themassoftheleftventriclemayrarelybe
increasedratherthandecreaseddespitethecavitaryhypoplasia.Theleftatrium
isusuallysmall,althoughtherecanbehypertrophyoftheleftatrialwalls.Some
patientscanhaveanenlargedatrium,particularlytheappendage.Theoval
foramenisusuallypatent,butinuptoone-tenthofpatients,theatrialseptum
willbeintact.Itcanbeaneurysmal,withprotrusionintothecavityoftheright
atrium(Fig.69.9).

FIG.69.7 Variationsfoundattheatrioventricularjunctioninthesettingof
hypoplasticleftheartsyndrome.Left,Mitralstenosis.Right,Mitralatresia
duetoabsenceoftheleftatrioventricularconnection.Fibroelastosisofthe
leftventricleisfoundonlyinthesettingofmitralstenosis.


FIG.69.8 Criticalaorticstenosisthatfulfillsthecriteriaforinclusionasan
exampleofhypoplasticleftheartsyndrome.Therightventricleisapex
forming,andthehypoplasticleftventricleisthick-walled,witha
fibroelastoticlining.