Andersons pediatric cardiology 203
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CirculatoryPatternsinFetalCongenital
HeartDisease
Themeanvesselflowsandoxygensaturationsfoundinapreliminarystudyofa
groupoffetuseswitharangeofmoresevereformsofCHD,obtainedusingthe
MRItechniquesdescribedabove,areprovidedinTable7.4.18Althoughthe
numberofpatientsineachgroupisrelativelysmall,particularlyforthe
oximetry,someexpectedhemodynamicpatternscanstillbeappreciated.Many
oftheseareverymuchexpectedandstraightforward.Forexample,whenone
sideoftheheartisobstructed,thereisacompensatoryincreaseinbloodflow
throughtheunobstructedside.Forexample,inhypoplasticleftheartsyndrome,
whereascendingaorticflowissignificantlyreduced,flowacrossthemain
pulmonaryarteryandductusarteriosusaremarkedlyincreased.Similarly,in
lesionscharacterizedbyrightheartobstruction,liketetralogyofFallotand
tricuspidatresia,wehaveobservedsignificantincreasesinascendingaorticflow
withdiminishedflowinthemainpulmonaryarteryandarterialduct.In
transpositionofthegreatarterieswehavenotedareversalofthenormal
relationshipbetweenthemainpulmonaryarteryandascendingaorticflows.In
thenormalfetalcirculation,mainpulmonaryarteryflowexceedstheascending
aorticflow.Thisispossibleinthefetalcirculationbecauseofthepresenceof
shuntsattheforamenovaleandductusarteriosusandpresumablyreflectsthe
greatervenousreturntotherightventricle.Intransposition,ascendingaortic
flowishigherthanmainpulmonaryarteryflow,whichislikelyduethe
discordantventriculoarterialconnectionsthatresultintheaortabeingconnected
tothedominantrightventricle(Video7.2).Despitethesevariationsinthe
outputsoftherightandleftheart,fetalorganperfusionappearstobereasonably
wellmaintained.Forexample,pulmonarybloodflowisratherstableacrossall
oftheseformsofCHD,andsimilartopulmonarybloodflowinnormalcontrols.
IfSVCflowistakenasasurrogateforcerebralbloodflowthencerebralblood
flowisalsowellmaintainedinmostformsofCHD.Theexceptiontothismay
beinthosefetuseswithmoresevereformsofEbsteinanomaly.FetalEbstein
anomalyisassociatedwiththelowestcombinedventricularoutputswehave
observedinfetuseswithCHD,andthiscanbeassociatedwithlowercerebral
bloodflow.OthertypesofCHDwithsingleventriclephysiologyarealso
associatedwithareductionofcombinedventricularoutputintherangeof10%
to20%.Whilecerebralandpulmonaryperfusionarerelativelywellmaintained,
thisreductionincardiacoutputisassociatedwithadropinumbilicalbloodflow.
Table7.4
PreliminaryHemodynamicPatternsinFetalCongenitalHeart
DiseasebyMagneticResonanceImaging
Normal
HLHS
TOF
TGA
Ebsteinanomaly
Tricuspidatresia
n
33
14
12
13
5
7
MEANBLOODFLOW(ML/MIN/KG)
CVO AAo MPA SVC DAo UV DA
469
208 246
137 237 130 180
429
56
368
141 220 120 298
482
387 84
129 261 140 78
498
272 211
170 250 133 133
285
207 150
101 162 112 110
414
229 173
138 195 80 125
MEANSAO2(%)
PBF n UV AAo MPA
71
33 80 59
52
78
5 80 48
48
79
10 68 53
50
83
7 71 46
53
71
4 78 46
44
73
5 73 47
50
DAo
53
50
50
49
45
47
SVC
45
36
38
39
33
36
AAo,Ascendingaorta;DA,ductusarteriosus;DAo,descendingaorta;HLHS,hypoplasticleft
heartsyndrome;MPA,mainpulmonaryartery;PBF,pulmonarybloodflow;SVC,superiorvena
cava;TGA,transpositionofthegreatarteries;TOF,tetralogyofFallot;UV,umbilicalvein.
Inadditiontothereductioninumbilicalflowseeninfetuseswithsingle
ventriclehearts,CHDappearstobeassociatedwithmodestreductioninthe
oxygencontentofumbilicalvenousblood.Thismayreflectstructural
differencesthathavebeendescribedonpathologicexaminationoftheplacenta
inpregnanciesaffectedbyfetalCHD.19–21Inourpreliminaryexperienceof
performingfetalMRoximetry,theotherstrikingandalmostuniversalfindingin
fetuseswithCHDisthereductioninascendingaorticoxygensaturation.
Individualexamplesofoximetrydatacollectedfromfetuseswithdifferenttypes
ofCHDareshowninFig.7.12andillustratesomeofthedifferenthemodynamic
mechanismsleadingtothisaorticdesaturation.Forexample,intranspositionof
thegreatarteries,theusualstreamingofwell-oxygenatedbloodtowardtheleft
heartviatheductusvenosusandforamenovaleresultsinthisbloodbeing
directedtowardthepulmonarycirculation.Meanwhile,moredesaturatedblood
fromtheinferiorvenacavacombineswithSVCbloodreturningfromthe
cerebralcirculationandisredirectedtotheascendingaorta.Thisisillustratedby
theT2mapsfromafetuswithtranspositionshowninFig.7.13.Similarly,in
tetralogyofFallot,althoughtheusualstreamingmayresultinnormaloxygen
saturationsinleftatriumandventricle,right-to-leftshuntingattheventricular
septaldefectresultingfromrightventricularoutflowtractobstructiondilutesthe
leftventricularoutputwithmoredeoxygenatedbloodfromtherightheart.In
hypoplasticleftheartsyndrometherecanbenoeffectivestreamingbecauseflow
throughtheleftsideoftheheartiscompletelyobstructedandthereiseffectively
onlyonecardiacoutlet.Inthisarrangementthereismixingoftheentirevenous
returnintherightatriumandventricle,andallcompartmentsofthefetal
circulationaresuppliedwithbloodofasimilaroxygencontent.Inadditiontothe
interruptionoftheusualpreferentialstreamingofoxygenatedbloodtowardthe
ascendingaorta,thereductionincombinedventricularoutputandassociated
dropinumbilicalflowresultsinareductioninoverallfetaloxygendelivery.
Thiscombinationofhemodynamiceffectsisassociatedwithsomeofthelowest
ascendingaorticsaturationswehaveobserved.Fetalbrainblood-oxygen-level
dependentmeasurementsobtainedinnormalcontrolsandfetuseswithCHDalso
suggestthatoxygensaturationsarelowerinthebrainsoffetuseswithCHD,and
theimplicationsofthisfindingintermsofbraindevelopmentarediscussedin
moredetailbelow.22
FIG.7.12 Magneticresonanceoximetryfindingsinfetuseswithcongenital
heartdisease.AAo,Ascendingaorta;DA,ductusarteriosus;FO,foramen
ovale;HLHS,hypoplasticleftheartsyndrome;IVC,inferiorvenacava;LA,
leftatrium;LV,leftventricle;MPA,mainpulmonaryartery;PBF,pulmonary
bloodflow;RA,rightatrium;RV,rightventricle;TGA,transpositionofthe
greatarteries;TOF,tetralogyofFallot;UV,umbilicalvein.
