Andersons pediatric cardiology 1906
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (102.71 KB, 3 trang )
lessthan16.6mL/kg/min.CI,ConfidenceintervalHR,heartrate.(From
FernandesS,AlexanderME,GrahamDA,etal.Exercisetestingidentifies
patientsatincreasedriskformorbidityandmortalityfollowingFontan
surgery.CongenitHeartDis.2011;6[4]:294–303.)
ConsequenttoimprovedsurvivaltheFontanpopulationisbecomingolder,
withtheaverageagepredictedtoincreasefrom18yearsin2014to23in2025
and31yearsin2045.32Theeffectivemanagementofthesepatientswilldepend
ontheidentificationofthoseatgreatestriskofdecline,aswellaspotentially
modifyingthecurrentapproachtostagedreconstructiononanindividualbasis.
Well-definedpatientsurveillancestrategieswillallowphysicianstodeliver
timelytargetedinterventionswiththeaimofincreasinglongevityandqualityof
life(QOL).
ConsequencesoftheFontanCirculation
TheFontancirculationischaracterizedbyelevatedcentralvenouspressure
(CVP)andaloworlow-normalcardiacoutputwithalimitedcapacityto
increasecardiacoutputwithexercise.Arrhythmiasarecommonandmaybe
causedbyatrialdistension,especiallyinthecaseoftheatriopulmonaryFontan,
orbyscarringsubsequenttosurgicalinterventions.ElevatedCVPandreduced
cardiacoutputadverselyaffectthefunctionofanumberoforgans,includingthe
hematologic,renal,liver,andlymphaticsystems.Manyoftheresultingproblems
haveaninsidiousonset,but,asthetimepasses,theycontributevery
significantlytomorbidity,mortality,andQOLlateaftertheFontanprocedure.
ImpairedExerciseCapacity(seealso
Chapter23)
PerformanceoftheFontancirculationislimitedatrestandwithexercise,even
withoptimalanatomicandcirculatoryconditions.Thisremainsanissue
regardlessofthetypeofFontanprocedure13,34–37andsuggeststhattheproblem
relatesinalargeparttotheinherentlimitationsofthecirculationitself.Inthe
normalcirculation,thesubpulmonaryventriclehasanimportantroletoplayin
augmentingcardiacoutputwithexercise.Itsabsenceiscentraltothelimited
exercisecapacityobservedintheFontanpopulation(Fig.73.7).Themagnitude
ofthereductioninexercisecapacityisbestdemonstratedbycardiopulmonary
exercisetesting.34,38–40Maximalexercisecapacityisdeterminedbythehighest
uptakeandutilizationofoxygenbythebodyduringmaximalexercise(VO2
max)basedonachievingaplateauofVO2despiteanincreaseinworkload.41,42
ThehighestachievedVO2value(VO2peak)isusedasasubstitutewhenthis
plateauisnotachieved;acommonoccurrenceintheFontanpopulation(Fig.
73.8).Inastructurallynormalheart,themajorfactorlimitingVO2maxis
cardiacoutput,whichaccountsfor70%to85%ofvariance,withtheremainder
beingderivedbyotherfactors,includingpulmonaryandskeletalmuscle
functionandcellularmetabolism.41,43Multiplestudieshavedemonstrated
reducedVO2peakorVO2maxinFontanpatients.31,37–39,44–46Importantly,a
lowerVO2peakisassociatedwithanincreasedriskofmorbidityand
mortality.21,31,45Thereisalsoreducedworkloadatmaximaleffort,avariable
reductionofVO2atventilatoryanaerobicthreshold,areducedpeakO2pulse,
andchronotropicincompetencewithabluntedpeakheartrate
response.37–40,44–46
