Andersons pediatric cardiology 1829

FIG.70.7 Decompressingvenovenouscollateral.(A)Anteroposterior
projectionand(B)lateralprojectionofanangiographicimagetakenwith
contrastinjectedintothebrachiocephalicvein.Theimagewastaken2
weeksafterasuperiorcavopulmonaryconnectiondueprogressive
hypoxemia(systemicoxygensaturation65%).Theasteriskdemonstratesa
venovenouscollateral“decompressing”thehigher-pressuresuperior
systemicvenoussystemintothelower-pressurepulmonaryvenous
system.Temporarypacingwiresareseenontheatriumandventricle.
LUPV,leftupperpulmonaryvein.SeeVideos70.1to70.5forresults
followingcoilembolization.(CourtesyJoshuaP.Kanter,MD,Children's
NationalMedicalCenter.)

Animportantclinicalobservationduringstagedreconstructionhasbeenthe
presenceofsignificanthypoxemiainsmalleroryoungerinfants(e.g.,lessthan
~4kgor~3months)whoundergoasuperiorcavopulmonaryconnection,
frequentlyresultinginalongerhospitalstayandincreasedresource
utilization.76–80Duringcardiaccatheterization,pulmonaryvenousoxygen
saturationsaretypicallynormal.Despitethepresenceofsignificanthypoxemia
andlowcalculationsofpulmonarybloodflow,significantdecompressing
venovenouscollateralsarefrequentlyabsentonvenousangiography.The
etiologyofthedecreasedQpandsignificanthypoxemiahasthusfarbeen
unexplained.Experimentally,inpatientswithastructurallynormalheart,
antegradecerebralbloodflowhasbeenshowntoremainnormaloverwide
rangesofincreasedintracranialpressure,aswouldbeexpectedsecondaryto
increasedpressureinthesuperiorcavalvein.ThereforeelevatedPVRdoesnot
decreaseantegradecerebralbloodflow;indeed,thishasbeenshowninelegant
studiesbyFogeletal.utilizingmagneticresonanceimaging.81Wespeculatethat


thedecreasedQpandsignificanthypoxemiaseenintheseinfantsmaybecaused
byvenovenouscollateralsthatdrainposteriorlyandinferiorlyfromtheheadand

neckviathecerebrospinalvenoussystem(Fig.70.8).Thisparaspinalvenous
networkiswithoutvalvesandincludestheBatsonplexus,anetworkofveins
thoughttoregulateintracranialpressurethroughthebalanceofcerebrospinal
fluidproductionandvenousdrainage.82-87Decompressionofvenousreturn
awayfromthesuperiorcavalveinposteriorlythroughthissystemmaycause
reducedpulmonarybloodflow;however,identificationofthismechanism
cannotbedeterminedeitherbyechocardiographyorvenousangiography.
Studiesarecurrentlyunderwaytoassessflowthroughthecerebrospinal
circulationasapossiblecauseofdecreasedpulmonarybloodflowand
significantpostoperativehypoxemiainthesesmallinfantswithaGlenn
circulation.


FIG.70.8 Cerebrospinalvenoussystem.(A)Redirectionofcerebral
venousreturnmayoccurintheearlypostoperativeperiod,bypassingthe
pulmonaryarteriestoconnectwithlowerbodyvenousreturnandcausing
decreasedpulmonarybloodflowandhypoxemia.(B)Venousreturnfrom
thehead,ratherthandrainingthroughthehigherpressurejugularveins
andsuperiorcavalvein,drainsthroughthebasilarvenousplexus,which
connectswiththeBatsonplexus—avalvelesssystemofveinsconnecting
theparavertebralveinsinferiorlytowardthepelvis.(A,FromBreschetG,
Recherchesanatomiquesphysiologiquesetpathologiquessurlesystáeme
veineux.Paris:Rouenfráeres;1829.CourtesytheSidneyTobinick
collection.)

Followingthetotalcavopulmonaryconnection(Fontanprocedure),upper-and
lower-bodyvenouspressuresareequal;thereforetheonlypressuregradientin