Andersons pediatric cardiology 1930

criteria,listingstatus,andorganallocation.


FutureDirections
Modificationsintreatmentstrategieshaveresultedinatremendousimprovement
insurvivalforthosewithafunctionallyuniventricularheartsincethefirst
Fontanoperationmorethan40yearsago.Theseincludestagedpalliationwith
anintermediatebidirectionalGlennshuntandmodificationsoftheFontan
procedurethatresultinimprovementsinefficiencyofthecirculationandreduce
therateoflatearrhythmia.Transformationaladvancesinareassuchas
immunosuppressionortargetedstemcellimplantationmaychangethetreatment
pathwayofpatientswithafunctionallyuniventricularheartinitsentirety,by
vastlyincreasingorganavailabilityandlongevity,developingdestination
intravascularpumps(seelater),orallowinggrowthofhypoplasticventricles.In
theabsenceofprogressintheseareas,incrementalimprovementsinoutcome
willinvolveinterventionsthatfurtheroptimizetheFontancirculationand
improvehealthandwell-being.Areaswherepreliminaryinformationis
encouragingandfurtherinformationislikelytoemergearedetailedinthe
followingparagraphs.

SelectivePulmonaryVasodilators
Inatwo-ventriclecirculation,exerciseresultsinatwofoldtofourfoldincreasein
cardiacoutputandanincreaseinpulmonaryvascularresistance.Leftventricle
preloadismaintainedthroughasubstantialincreaseinrightventriclework.In
theabsenceofasubpulmonaryventricle,peakexercisecapacityisreducedas
thereisalimitedcapacitytoincreasesystemicventriclepreload,thelatterbeing
dependentontheCVPandpulmonaryresistance.IntheFontancirculation,
pulmonaryvascularresistancehasbeendescribedasadamholdingback
systemicvenousreturn.407“Loweringthedam”wouldthusprovidemore
pulmonaryvenousreturntothesystemicventricle(preload)atalowerCVP(see
Chapter70).Investigationstodatehavefocusedonthesafetyofpulmonary

vasodilatorsandtheirpotentialtoincreaseexercisecapacityinthispatient
population.Resultsofsmall,well-designedstudiesintheFontanpopulation
havedemonstratedthattheseagentsaresafeovertheshortterm.61,62,408The
mostcommonsideeffectsareflushingwiththephosphodiesterase5inhibitor
sildenafilandtheendothelinreceptorantagonistBosentan,andaslightreduction
inhemoglobinwithBosentan.Neithermedicationisassociatedwithadramatic


improvementinexercisecapacity;however,relativelysmallincreasesin
ventilatoryefficiencyandmaximalandsubmaximalexercisecapacityhavebeen
demonstratedinseveralstudies,61,62andanimprovementinfunctionalclassand
reductioninBNPhasalsobeenreported.62
Thepotentialtoreducepulmonaryvascularresistanceoverthelongtermhas
implicationsbeyondexercisecapacity.Muchofthelatemorbidityassociated
withtheFontancirculationisduetochronicallyelevatedCVPandlowcardiac
output.Aslowdeclineinfunctionalclassandliverandrenalfunctioniswell
described,asisagradualincreaseinpulmonaryvascularresistance.Whetherthe
latterisrelatedtoendothelialdysfunction,chronicmicroemboliandthrombosis,
oraresponsetolowcardiacoutputremainsapointofconjecture.Thepotential
forlong-termpulmonaryvasodilatortreatmenttomodifythepatternofgradual
butrelentlessend-organdysfunctionisattractive.However,thereisaconcerning
growinglackofequipoisebecausemanypractitionersarecurrentlyusingthese
medicationsroutinely,priortolargerstudiesdeterminingefficacy.Itisimportant
toemphasizethatsafetyoverthelongtermmustbedetermined,giventhe
generallyabnormaldrugclearanceseeninmanypatientswithaFontan
circulation.
Itiscriticallyimportanttoemphasizethatlargelong-term,randomizedstudies
willberequiredtobetterdefinetheclinicalutilityofthesemedicationsto
improvetheefficiencyoftheFontancirculation,aswellastoidentifysubsetsof
patientsmostlikelytobenefitfromtreatment.

ExercisePrograms
Theroleofexerciseprogramsinimprovinghealthandwell-beingintheFontan
populationiscontroversial.Nevertheless,emergingevidencesuggeststhat
specificexerciseprogramsmayhaveabeneficialeffectonexercisecapacity.336
Inaddition,theamountofphysicalactivityundertakenbyFontanpatientsis
lowerthancontrolsandcorrelateswithperceivedhealthstatus.331,409Increasing
physicalactivitymayhaveapositiveimpactonwell-beingthroughimproved
self-esteem,increasedmusclemass,andreducedbodymassindex.410
Inthenormalcirculation,skeletalmuscleaugmentsvenousreturnduring
exercise.ThisfunctionisparticularlyimportantintheFontancirculationgiven
theabsenceofasubpulmonaryventricle.Therelativecontributionofperipheral
skeletalmuscleandchestwallmechanicstostrokevolumeaugmentationduring
exercisehasbeenelegantlydemonstrated(Fig.73.30).334Stokevolumeand