Andersons pediatric cardiology 1824

functionallysinglesystemicventricle.Bloodfromtheplacentaentersthefetus
throughtheumbilicalveinsandthenenterstheportalsystem,inferiorvenacava,
andultimatelythesystemicvenousatriumviatheductusvenosus.Infetuses
withastructurallynormalheart,umbilicalvenousbloodhasanoxygen
saturationofabout80%to85%andaPO2ofabout32to35mmHg,although
thismaybediminishedinfetuseswithCHD.34
Thedramaticchangesinphysiologyseenwiththetransitionalcirculationin
neonateswithstructurallynormalhearts(fallinPVR;increaseinpulmonary
bloodflow;increaseincombinedventricularwork;increaseinsystemic
ventricularafterload;closureoftheductusvenosus,ductusarteriosus,and
foramenovale,amongothers;seealsoChapter15)resultinhemodynamic
abnormalitiesthatarequitevariable,dependingontheindividualanatomyofthe
fUVHandthetimingof“transition.”Itisbeyondthescopeofthischapterto
definethesechangesforthemyriadofindividualstructuraldefectswith“single
ventriclephysiology”;sufficeittosaythattheinitialprinciplesofpresurgical
managementareinmostcasesdirectedtowardmimickingthefetalcirculation:

•Ensuringcontinuedpatencyoftheductusarteriosus
•Minimizingrestrictionattheatriallevel(ifpresent)
•ManipulatingthedistributionofthefUVHcardiac
output,typicallywithstrategiesthatkeepPVR
elevatedandsystemicvascularresistancelow
AsthePVRcontinuestofallafterbirth,ahigherproportionoftheventricular
outputisdirectedtothepulmonaryvascularbedandthevolumeworkofthe
ventricleincreases.Althoughthismaybetoleratedfordaysorevenweeks,the
increaseinvolumeworkwilleventuallyleadtosignsandsymptomsof
congestiveheartfailure.Asacompensatorymechanism,thesystemicvascular
resistancerises,furtherredirectingbloodintothepulmonaryvascularbed,
worseningheartfailure,andeventuallyleadingtocirculatoryfailure.Thebaby
mayshowalltheclassicsignsofcirculatoryinsufficiencyincludingtachycardia,
pallor,oliguria,andsoforth.However,clinicalexperiencehasshownthatthe

developmentofheartfailureisaslow,gradualprocessoverdaystoweeksinthe
majorityofneonateswithanfUVHduringtransition,providingthereis
continuedpatencyofthearterialduct.Aswaslearnedintheearlydaysof


cardiactransplantationasaprimarysurgicalstrategy,manybabiestoleratethis
relativelyhighratioofQptoQsandcanmaintaintheirsystemicoxygendelivery
forweeksorevenmonths.35,36Ifthecombinedcardiacoutput(Qp+Qs)canbe
maintained,ahighoxygensaturationmayresultinadequateoxygendelivery,
albeitattheexpenseofavolumeoverloadedventricleandpossibleprogressive
congestiveheartfailure.Inthepreoperativeneonatewithapatentarterialduct,
wehavefoundthatacutedeteriorationfromincreasedpulmonarybloodflowin
isolationisarareevent.


ClarificationsandProposedChangesto
TerminologyUsedintheNeonate,Infant,
andChildWithaFunctionally
UniventricularHeart
“ParallelCirculation”
Previously,thecirculationoftheneonatewithafUVH,bothbeforeandafter
surgicalpalliation,hasbeendescribedasaparallelcirculation.Wefeelthatthis
isaninaccuratetermforbabieswithafUVH,asatrulyparallelcirculation
shouldbereservedforneonateswithunrepairedtranspositionofthegreat
arteries(seeChapter37).Moreaccurately,thefUVHmustdistributethe
ventricularoutputtoboththepulmonaryandsystemicvascularbeds,andifthere
isatrioventricularvalveregurgitation,retrogradetotheatrium.Thus,ratherthan
a“parallelcirculation,”thephysiologyintheneonatewithafUVHisbetter
describedasamultidistributioncirculation(Fig.70.2).

FIG.70.2 Multidistributioncirculationintheneonatewithafunctionally
univentricularheart.Thevariousfactorsaffectingoxygendelivery,both