Andersons pediatric cardiology 1908

patients,suggestingthatremodelingisinadequate.34,36,48–51Diastolic
dysfunctiontransmitsincreasedfillingpressurestothepulmonaryveins.This
hasaprogressivenegativeimpactonthepulmonaryvascularbedandsystemic
venousreturn,leadingtofurtherrestrictionofexerciseperformance.52Increased
systemicvenousstiffnessandreducedcapacitanceaugmentsystemicreturnin
theFontancirculationatrest,buttheseadaptivemechanismsarelesseffective
withexercise.52,53
Pulmonaryvascularresistancelimitssystemicventriclepreloadandcardiac
outputintheFontancirculationbecauseitsetsthelevelofenergyrequiredto
deliverbloodfromthesystemicveinstothesystemicventricle.37,39,54,55A
numberoffactorshavethepotentialtoadverselyimpactonpulmonaryvascular
resistance.Forexample,vascularcompliancemaybecompromisedbythelack
ofpulsatileflow,whereasreducedwallshearstressmayleadtomaladaptive
changesinlungvasculatureandincreasedpulmonaryvascularresistance.56
Abnormalmicroscopicpulmonaryvascularchangeshavebeendescribedinthe
Fontancirculation,ashasimpairedpulmonaryarterygrowth.57–60Othershave
describedabnormalpulmonaryvascularreactivitywithexercise.52
Althoughthemechanismofabnormalpulmonaryvascularbehaviorisunclear,
evenasmallincrementofpulmonaryvascularresistancehasthecapacityto
reducetheabilitytoaugmentcardiacoutputwithexercise.Thishasgenerated
interestintheuseofpulmonaryvasodilatortherapyintheFontanpopulation.
However,themixedresultsofthesemedicationsonFontanexercise
performancesuggestthatthefactorsresponsibleforexerciserestrictionare
complex.61–65

ChronotropicIncompetence(SeealsoChapter
22)
Theinabilityofthehearttoincreaseratecommensuratewithdemandisa
recognizedpredictoroffuturecardiovasculareventsandoverallmortalityin
othersettingsofcardiovasculardisease,includingheartfailure.66Chronotropic
incompetenceisamarkerofdysautonomicfunctionandreducedsinusnode

reserve.66,67IntheFontanpopulationanimpairedheartrateresponsetoexercise
isacommonfinding.37–40,45,46Thereissomedebateastoitsrelative
contributiontoimpairedexercisecapacity,39,68withsomeevensuggestingthatit
mayformausefuladaptiveresponsewhenthereisdiastolicdysfunction.69Sinus


nodedysfunctionmayberelatedtodamagetothesinusnodeanditsarterial
supplyduringcardiacsurgery.Moremoderncavopulmonaryconnectionshave
resultedinbetterpreservedchronotropy,39,44butsinusnodedysfunctionisnot
eliminatedcompletelybecausecontributorsmayincludepriorbidirectional
Glennorhemi-Fontansurgeries.70Theprognosticimplicationofchronotropic
incompetencewithintheFontanpopulationisunclear.31,71

RestrictiveLungDisease
Intheabsenceofasubpulmonaryventricle,theFontancirculationrelieson
efficientlungmechanics,withchangesinintrathoracicpressureduring
respirationactingasasuctionpumptodrawbloodthroughthelungs.Itis
increasinglyrecognizedthatoptimizedlungparenchymaisanimportantpositive
contributortotheFontancirculationbothatrestandunderexerciseconditions.
Restrictivepulmonaryfunction,asdemonstratedbyreducedforcedvital
capacityandforcedexpiratoryvolumein1secondiswelldescribedinpatients
withcongenitalheartdiseaseandisparticularlyapparentinthosewithaFontan
circulation.58,72–75Thispatternofabnormalrespiratoryfunctionismultifactorial
withcontributionsfromthoracicsurgeries,pleuralstiffness,intrinsiclung
developmentabnormalities,andFontanpulmonaryvascularflowdynamics.Side
effectsfromtheuseofmedications,especiallyamiodarone,mayalsoplaya
role.72,74–76Underexerciseconditions,restrictivelungfunctioncanmanifest
withreducedO2pulse,higherpeakminuteventilation(VE),andreduced
ventilationefficiencywithhigherVE/VCO2slope.31,45,77Inaddition,several
studieshavefoundasignificantcorrelationbetweenimpairedrestingpulmonary

functionandreducedpeakVO2maxonexerciseintheFontanpopulation.31,58,73
Asmallinterventionalstudyfocusedonreducedinspiratorymusclestrengthin
Fontanpatientsbyinstitutinginspiratoryrespiratorymuscletraining.Following
training,restinginspiratorymusclestrength,cardiacoutput,andejectionfraction
increased,whereasduringexercisetherewasanimprovementinventilatory
efficiency.78
Therelativecontributionofthepulmonarycirculationandcardiovascular
mechanicstoexerciserestrictioninFontanpatientsisyettobefully
understood.79Furtherresearchwillimprovetheunderstandingofthese
limitationsandleadtonewwaysof“empowering”theFontancirculationunder
exerciseconditions.


ImpairedSomaticGrowth
Somaticgrowthisimpairedduringandfollowingstagedreconstructionfor
childrenwithafunctionallyuniventricularheart.80–85Weightandheight
parametersaremostoftenwithinthenormalrangeatbirthintheabsenceof
prematurityorgeneticabnormalities.80,82,85,86Followingtheinitialsurgical
procedure,thereisasignificantdecreaseinbothheightandweightzscore.80–85
WeightfollowsatrajectoryofrelativerecoveryafterthebidirectionalGlennor
hemi-Fontanoperation,andfollowingFontancompletioninmostchildren.80–86
However,heightdoesnotdemonstratethesametrend.80–83,85–87Heartfailure,
PLE,thepresenceofvenovenouscollaterals,andsignificantatrioventricular
valveregurgitationmayhaveanegativeimpactonweightandheighttrajectory,
althoughtheseassociationshavenotbeendemonstratedinaconsistent
way.80–83,85Byadulthood,maleswithaFontanareshorterthannormal
population.87Thisrelationshipislessstrikinginfemales.87Mechanismsforthe
reductioninheightpotentialmayincludelowerbonedensityandreduced
musclemass.85,88Ofinterest,butasyetunconfirmed,lowerexercise
participationinFontanpatientsmayimpactonbonegrowthandsubsequent

bone/muscledevelopment.81,82,88,89Anotherpotentialcontributortoreduced
bonegrowthisprolongedhypoxemiapriortoFontancompletion,85,88althougha
fenestrationaftertheFontanoperation(amarkerforhypoxemia)doesnotappear
toinfluenceheightrecovery.83,86TheimpactoftheFontancirculationon
insulin-likegrowthfactors(IGFs)andgrowthhormoneandtheirinteractionwith
somaticgrowthisyettobeestablished.90,91Inacross-sectionalstudy,lowerIGF
wasfoundinFontanpatientswithahigherbrainnatriureticpeptide(amarkerfor
heartfailure)andlowercardiacoutput.However,therewasnorelationship
betweenIGFandsomaticgrowth.Theauthorsconcludedthatlongitudinal
studieswererequiredtodetermineiftheserelationshipscontributedtoimpaired
somaticgrowthinthispopulation.92
Thereisconcernthatobesitytrendsseeninthegeneralpopulation93,94willbe
similarlyseenintheFontanpopulation.Althoughobesityislessprevalentin
Fontancohortscomparedwiththegeneralpopulation,aswellasotherformsof
congenitalheartdisease,therateisnotinsignificantandrangesfrom8%to
30%.85,88,95Moreover,thereisatendencytowardincreasingweightandbody
massindexfurtheroutfromFontansurgery.95,96GiventherelianceoftheFontan
circulationonoptimalventricularandvascularfunction,additionalacquired