Andersons pediatric cardiology 1823

FIG.70.1 SchematicrepresentationofflowthroughtheFontan
circulation.Theprimarylong-termgoalistoachievethehighestpossible
cardiacoutputatthelowestpossiblecentralvenouspressure(CVP).The
CVPisdeterminedbyaseriesofpotentialresistorsthroughthecircuit.
Optimaloutcomesareachievedbyminimizingobstructionandimpedance
toflowfromthesystemicvenouscompartmenttothefunctionalsingle
ventricle.(A)Potentialareasofobstructionareshowninalinearfashion.
(B)Representativeanatomicallycorrectillustration.Obstructiontoflow
alonganyofthepathways(arrowsinAorasterisksinB)reducesoverall
cardiacoutputand/orelevatescentralvenouspressure.


PhysiologyImmediatelyAfterBirth
ClinicalPresentation
Ingeneral,themajorityofneonateswithafUVHcanbebroadlycategorized
physiologicallywitheitherductal-dependentpulmonarybloodflow(right-sided
lesions)orductal-dependentsystemicbloodflow(left-sidedlesions;seealso
Chapter69).Thephysiologyoftheneonatewiththeseconditionsisdiscussedin
detailfurtheron.Uncommonly,aneonatemayhave(1)nosignificant
obstructiontoeitherthesystemicorpulmonarybloodflowor(2)nosystemic
outflowtractobstructionand“justtherightamount”ofanatomicobstructionto
pulmonarybloodflow(notcausinghypoxemia,pulmonaryhypertension,or
congestiveheartfailure).Individualizedmanagementplanswillhavetobe
developedforthesemoreuncommontypesoffUVH(seeChapter71).
However,ingeneral,mostneonateswithafUVHrequiresurgeryshortlyafter
birthandtendtopresentinoneoffourmutuallyexclusiveways.
1.Ifthediagnosishasbeenmadeprenatally,anexpectantteamof
caregiversmanagesametabolicallystableneonatewithprostaglandin
andminimalotherinterventions(seeSection2,PrenatalCongenital
CardiacDisease).
2.NeonatespresentingpostnatallywithafUVHandductal-dependent

pulmonarybloodflowwilltypicallyshowsignsofprogressive
hypoxemiaandrespiratorydistressuponconstrictionorclosureofthe
arterialduct.
3.NeonatespresentingpostnatallywithafUVHandductal-dependent
systemicbloodflowwilltypicallypresentwiththeacuteonsetofheart
failureand,intheworstscenario,shock,withmultiorgansystemfailure
uponconstrictionorclosureofthearterialduct.Thereistypically
decreasedsystemicperfusion,withincreasedflowtothelungs,largely
independentofthepulmonaryvascularresistance(PVR).Theperipheral
pulsesareweaktoabsent.Renal,hepatic,intestinal,coronary,and
centralnervoussystemperfusioniscompromised,possiblyassociated
withacutetubularnecrosis,necrotizingenterocolitis,whitematter
injury,cerebralinfarction,and/orhemorrhage.Inpatientswithaortic
atresia,aviciouscyclemayalsoresultfrominadequateretrograde


perfusionoftheascendingaortaandcoronaryarterialsupply,with
furthermyocardialdysfunctionandcontinuedcompromiseofflowtothe
coronaryarteries.Thus,onehastheparadoxicpresentationofa
profoundmetabolicacidosisinthefaceofarelativelyhighpartial
pressureofoxygen,occasionallyashighas60to70mmHg.Inthese
neonates,attheinitialpresentation,sepsisisfrequentlysuspectedbefore
thecardiacdiagnosisismade.28–30Fortunatelyanincreasingprevalence
ofaprenataldiagnosishasmadethisunfortunatesituationincreasingly
lesslikelyinthecurrentera(seeSection2).Also,routinescreeningwith
pulseoximetryhasminimizedthefrequencyofshockand/orprofound
hypoxemiainneonateswithoutaprenataldiagnosisofafUVH(see
Chapter89).
4.Finally,neonateswithafUVHinwhomtheductusremainspatentwill
presentwithsymptomsofmildcongestiveheartfailureandhypoxemia,

withorwithoutvisiblecyanosisoracardiacmurmurandnoend-organ
dysfunction.

FetalandTransitionalCirculation
Anunderstandingoffetalbloodflowpatternsandthechangesthatoccurafter
birth(describedindetailinChapter15)iscrucialtocomprehendingthe
physiologicchallengesfacingtheneonatewithCHDandparticularlythebaby
withafUVH.Afetuswitheitherleftorrighthearthypoplasiatypicallydoesnot
showsignificantintrauterinegrowthretardation;however,thereisgrowing
evidencethatuniventricularcardiacoutputmaybediminishedcomparedwith
thatofafetuswithastructurallynormalheart,withsecondaryeffectstothe
placentaanddevelopingbrain(seeChapters11and76).Inleft-sidedlesionsin
particular,decreasesinfetalcerebralbloodflowarepartiallybalancedbya
decreaseincerebrovascularresistance,allowingthefetustomaintainoxygen
andsubstratedeliverytothebrain.Despitetheseadjustments,brain
abnormalitiesinneonateswithCHDarecommonandwelldescribed(see
Chapter76).31–34
Metabolicdemandsonafetusarelimited,andthefluid-filledhigh-resistance
fetallungsreceiveonlyabout10%oftheventricularoutput.Intheabsenceof
significantatrioventricularvalveregurgitation,oxygendeliveryandgrowthof
thefetusarethereforedeterminedonlybytheabilityoftheplacentatoprovide
oxygen-richbloodtothesystemicvenousatriumandthecontractilityofthe