Andersons pediatric cardiology 561
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ImplantableCardioverter/Defibrillators
Suddencardiacdeathistheleadingcauseofdeathinpatientswithcongenital
heartdiseaseandheritablegeneticcardiacdisease.ICDscanbelifesavingin
patientsatriskofdevelopinghemodynamicallyunstablelethalarrhythmias.
ICDshavebecomethetreatmentofchoiceinpreventingsuddencardiacarrestin
someconditions,andmanystudieshaveidentifiedclearadvantagesover
antiarrhythmictherapy(Fig.22.32).
FIG.22.32 Ananteroposteriorchestradiographshowingasinglechamber(ventricular)implantablecardioverter/defibrillator(ICD)system.
Thesingle-coilICDleadisaffixedtotheRVmyocardiumviatheleft
subclavianvein.TheICDgeneratorisplacedsubpectorally.
TheNationalICDRegistryreportforcombinedadultandpediatricvolumesin
1yearenrolled850,068ICDprocedures,averagemonthlyenrollmentwas
12,537,andofthis347(0.13%)werepediatricpatients.186ICDimplantationfor
primarypreventionwas73.8%;forsecondarypreventionitwas23.5%.186Ofthe
patientsundergoinggeneratorchanges,25%hadreceivedanICDdischargeor
antitachycardiapacingtherapy.OftheICDshocks,85%wereappropriateand
14.9%wereinappropriate.Adverseeventsoccurredin2.2%ofalloperations.186
TheNationalICDRegistrycanprovideevidence-baseddatatoguidefuture
decisionmaking.186
Inpatientswithcongenitalheartdiseaseandconcerningsymptomssuchas
syncope,ventricularstimulationtestingmaybeworthwhiletoassistinrisk
stratification.Thereisevidencetomeritprogrammedventricularstimulationto
risk-stratifypatientswithtetralogyofFallot,butinfactthesamemaynothold
trueforthepatientfollowinganatrialbaffleprocedure.154,155,187Thereis
evidencethatpatientsfollowingatrialbaffleproceduresmaybeatagreaterrisk
ofsuddendeathduringexertion.Thismaypartiallybeexplainedbytheunique
RVarchitecture,whichisnotdesignedtobeasystemicventricle,andthefact
thatasinglerightcoronaryarterysuppliesthesystemicRVasopposedtothe
usualtwoleft-sidedcoronaryarteries.Symptomsofexertionalchestpain,
palpitations,andsyncopeareofespeciallygreatconcerninthepatientwhohas
undergoneanatrialbaffleprocedure.Arrhythmiasthatdeveloponatreadmillin
apatientafteraMustardorSenningprocedurerequirecarefulevaluation.
Sincelessthan1%ofICDimplantationsoccurinthepediatricpopulation,
nontraditionalapproachesarefrequentlynecessary.Thereforethehardware,
settings,andtreatmenttherapiesoftenneedcarefulattentiontooptimize
programmingforthepediatricandcongenitalpopulation.ICDshavedelivered
manyappropriatetherapiesinchildrenandsavedmanylives,butunfortunately
upto20%ofpatientsexperienceinappropriateshocks.Inappropriatetherapies
arenotbenignandquality-of-lifestudiesshowaninverserelationshipwithICD
discharges.188Commonriskfactorsaresupraventriculartachycardia,sinus
tachycardia,leadfracture,andT-waveoversensing.Programminglonger
detectiontimeshasshownthatmanyVTeventsself-terminateifgivenenough
timetoterminatespontaneously.Helpfultipstopreventinappropriatedischarges
areprogramminglongerdetectiontimes,exercisestresstestingtoidentifythe
uppersinusrate,programmingantitachycardiapacing,andcloseremote
monitoringtoidentifyanyimmanentriskfactors.Routineevaluationwithdevice
interrogationorremotetransmissioncanidentifysubtletiesofelectromagnetic
interferenceandextracardiacsignals;itcanalsocorrectanalysisofmorphology
templateswithmonitoredeventsinanefforttodecreaseinappropriateshocks.
Otherchallengestoconsiderincludepatientsize,accountingforfuturesomatic
growth,accesstotheheartduetosurgicalpalliation,orobstructedvasculatureor
conduits,intracardiacshunts,andriskforthromboemboli.187Patientswhoare
notcandidatesforatransvenoussystemmayrequireanepicardialsystem.There
arenovalidatedstudiesthathavedefinedalowerweightcutoffforcandidacyfor
atransvenoussystem.Althoughthereisnoconsensus,aweightofatleastof25
kgforpotentialcandidateshasbeenrecommended.189
IfanICDfailstoconvertaventriculararrhythmia,factorstoconsiderinclude
aninadequatedefibrillationsafetymargin,antiarrhythmicdrugsknownto
increasedefibrillationthresholds,low-amplitudeelectrograms,andhyperkalemia
andothermetabolicperturbations.Highdefibrillationthresholdsmayrequire
consideringasubaxillaryarrayoranalternativevector.Inpatientswithsevere
hypertrophiccardiomyopathyanddeviceslocatedintherightinfraclavicular
pocket,highoutputabove35Jmaybenecessaryforconversion.
SincealargepercentageoftheICDfailurerateisinfluencedbyleadsurvival,
amulticenterstudyonICDleadperformanceandtheriskofleadextractionin
childrenandcongenitalheartdiseasepatientswasperformed.190Thisstudy
consistedof878ICDpatients(44%withcongenitalheartdisease);theaverage
leadagewas2.3years,witha14%rateofleadfailure.190Thestudyconcluded
thatICDleadshaveage-relatedsuboptimalperformancethatvariedbyleadtype
andyoungerageatimplant.Thiswasanindependentriskfactor.Transvenous
leadextractionistechnicallychallengingandisnotwithoutariskofmorbidity
andmortality.
ICDuseinthepediatricandcongenitalheartdiseasepopulationtoprevent
suddencardiacdeathcontinuestogrow;withincreasedlifeexpectancythere
mustbeaproactiveplantoaddresstheneedformaintainingleadlongevityand
identifyingcircuitryandprogrammingoptimizationtopromotebatterylife.
AdvancesinICDhardwareandfunctionwillservetoexpandandimprovethe
careforthisvulnerablepopulation(Fig.22.33).
