Andersons pediatric cardiology 1661
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significantunderestimateoftheprevalenceofLVNC,as15%to45%ofpatients
maymeetatleast1MRIcriterionforLVNCinatleastonesegment.406,407The
maximumthicknessoftrabeculationsalsoappearstovarybygenderand
ethnicity,asmalesandpersonsofChineseorAfricanAmericandescenttypically
haveagreaterdegreeoftrabeculationwhenpresent.406,408
ClinicalOutcomes
TheclinicaloutcomesseeninpatientswithLVNCareusuallydeterminedbythe
developmentofcomplicationsassociatedwiththedisease,includingheart
failure,significantarrhythmias,andthromboembolism.409,410Ininitialreports
onLVNC,mortalityrateswerereportedtobe13%withinthefirstyearof
diagnosis,withthehighestriskassociatedwithheartfailureandventricular
arrhythmias.411However,subsequentreportsdocumentedbetteroutcomeswitha
slowerrateofprogressionofmyocardialdysfunctionandheartfailure.The
NationalAustralianChildhoodCardiomyopathystudyisanongoinglongitudinal
cohortstudyandreportedthecumulativeincidenceofsuddencardiacdeathin
patientswithLVNCtobe23%.232Bresciaetal.performedasingle-center,
retrospectivereviewof242childrenwithLVNCandfoundthat150(62%)
presentedwithordevelopedmyocardialdysfunction.412Inaddition,80(33.1%)
hadasignificantarrhythmia,6%experiencedsuddendeath,31died,and13
(5.4%)underwenthearttransplantation.Thepresenceofmyocardialdysfunction
wastheprimarydriverofmortality,althoughthosewitharrhythmiaswerealsoat
increasedriskofmortality.Childrenwithnormalcardiacdimensionsandnormal
myocardialfunctionwerefoundtobeatverylowriskforsuddendeath.Data
fromthePediatricCardiomyopathyRegistryfurthersupporttheideathat
outcomesaredrivenbythespecificLVNCphenotype(hypertrophic,dilated,
etc.).413Eachofthesestudieswasconductedatatertiarycarefacilityand
ambulatoryscreeningdataaregenerallylacking.
Asunderstandingofthediseasehasincreased,itisnowrecognizedthatthere
aresubtypesofit.Thereareatleasteightsuchsubtypes,including(1)benign
LVNC,(2)LVNCwitharrhythmias,(3)dilatedLVNC,(4)hypertrophicLVNC,
(5)hypertrophicdilatedLVNC,(6)restrictiveLVNC,(7)rightventricularor
biventricularLVNC,and(8)LVNCwithcongenitalheartdisease.404Benign
LVNCischaracterizedbynormalleftventricularsizeandwallthicknesswith
preservedsystolicfunction.LVNCwitharrhythmiashaspreservedsystolic
functionwithnormalLVsizebuthasclinicallysignificantarrhythmias,which
aretypicallydetectedatpresentation.DilatedLVNCischaracterizedby
concomitantLVdilationandsystolicdysfunction.HypertrophicLVNCis
characterizedbyleftventricularthickening,typicallywithasymmetricseptal
hypertrophy,inadditiontodiastolicdysfunctionandhypercontractilesystolic
function.HypertrophicdilatedLVNCischaracterizedasbeingamixed
phenotypewithleftventricularthickening,chamberdilation,anddepressed
systolicfunction.RestrictiveLVNCischaracterizedbyleftatrialorbiatrial
enlargement,diastolicdysfunction,andtypicallypreservedsystolicfunction.
Biventricularnoncompactionischaracterizedbyhypertrabeculationofboth
ventricles.Noestablishedcriteriaexistforhypertrabeculationoftheright
ventricle,makingthisachallengingdiagnosis,butitistypicallydiagnosedby
heavytrabeculationandthespongiformappearanceoftherightventricle.LVNC
withcongenitalheartdiseaseisincreasinglyrecognizedinclinicalpractice.
LVNChasbeenreportedwithalmostallcongenitallesions.Right-sidedlesions
includingtheEbsteinanomaly,pulmonicstenosis,pulmonaryatresia,tricuspid
atresia,anddouble-outletrightventriclearemostcommon,butassociationswith
left-sidedlesionsandseptaldefectshavebeenreported.414LVNCinthesetting
ofcongenitalheartdiseaseappearstohaveanimpactonperioperativeoutcomes.
Etiology
Basedonthenoncompactionhypothesis,LVNCissecondarytoafailureofthe
finalphaseofcardiacdevelopment,whichisthemyocardialcompaction
process.415Intheearlyembryo,theheartisameshofloose,interwovenmuscle
fibersseparatedbyintertrabecularrecessesthatlinktheleftventricularcavity
withthemyocardium.Themeshworkofmyocardiumbeginstocompact
betweenthefifthandeighthweekofembryonicdevelopment.Thisprocess
occursfromthebaseofthehearttotheapexandfromtheepicardiumtothe
endocardium,andtheintertrabecularrecessesarecompressedtocapillaries.The
compactionprocesscontinueswithongoingmyocardialgrowthandincreasing
intramyocardialpressure.Thecompactionofthemyocardiumistypicallymore
completeintheleftventriclethantherightventricle,leadingtothepresenceof
coarserrightventriculartrabeculationsinthematurehumanheart.Thefailureof
theleftventricletocompactisthoughttooccurbecauseofanarrestin
endomyocardialmorphogenesis,resultinginLVNCinthepostnatalheart.
MutationsinthemurinegenesDaam1,Casz1,Fkbp1aandBMP10,jmjand
Jarid2,andMibhavebeenimplicatedinthedevelopmentofLVNC,astheyare
allinvolvedincardiacmorphogenesis.404
SeveralgeneshavebeenimplicatedinthedevelopmentofLVNC,including
bothsarcomericandnonsarcomericgenes(seeTable61.1).Thefrequencyof
genefindingsissomewhatconfusedbytheco-occurrenceofLVNCandother
cardiomyopathyphenotypes(e.g.,hypertrophicLVNC,dilatedLVNC).416
Multiplechromosomaldeletionsandduplicationshavebeenreportedwith
LVNC,includingBarthsyndrome,1p36,trisomies18and13,Coffin-Lowry
syndrome,andSotossyndrome,amongothers.LVNCisprimarilythoughttobe
congenitalinnature,buttherearereportsintheliteratureofacquiredLVNC.
Thishasprimarilybeeninthesettingofneuromusculardisorders,high-level
athletes,andpregnantwomen.417–419
Pathology
Macroscopically,theheartischaracterizedbyprominenttrabeculae,
intertrabecularrecesses,andaleftventricularmyocardiumwithtwodistinct
layers:noncompactedandcompacted.Intheisolatedformofthedisease,thereis
normalLVsize,thickness,andsystolicfunction.Microscopically,thefindings
arevariableandnonspecific.
Pathophysiology
HeartFailure
InpatientswithLVNC,theriskofheartfailureisamajorconcern,andheart
failuremaybetheinitialpresentationofpatientswiththedisease.The
underlyingmechanismbehindmyocardialdysfunctionremainsunclear,butit
canbesystolicand/ordiastolicinnature.Patientsshouldbetreatedmedically,as
theywouldbeforheartfailureinthesettingofothercardiomyopathies(as
earlier).
Arrhythmias
SupraventricularandventriculararrhythmiasoccurfrequentlyinLVNCandmay
belife-threatening;ventriculararrhythmiasareprevalentinLVNCacrosstheage
spectrum.267,411,420–424Therelativeriskdifferencesbetweenchildrenandadults
