Andersons pediatric cardiology 552
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Fontanphysiology,asingleoraldoseof2mg/kgofsotalolsuccessfully
convertedIARTorectopicatrialtachycardia(EAT)in84%.151
ChronicmedicalmanagementofIARTinACHDpatientshasbeen
discouraging,andalthoughablationcancurethesetachycardias,thistoocanbea
challenge,asmultipletachycardiacircuitsmaybepresentintheseverydilated
andhypertrophiedatria.Vascularaccessandlackofaccesstothechamberof
interestfurthercomplicatetheseprocedures.152
AtrialFibrillation
AFisuncommoninpediatricpatientsbutisseenincreasinglyintheaging
ACHDpopulation.Asintheagingpopulationwithoutcongenitalheartdisease,
AFisassociatedwithsystemichypertensionandincreasingage.However,its
sharpincreaseinprevalenceappearstooccurataconsiderablyyoungeragein
patientswithcongenitalheartdiseaseascomparedwiththegeneral
population.148Inarecentstudy,AFaccountedforlessthan10%ofatrial
arrhythmiasinpatientsunderager20yearsandwasthemostcommon
presentingarrhythmiainthose50yearsofageorolder.148Inthisstudy,among
the136ACHDpatientswhohadattainedtheageofatleast50years,overhalf
haddevelopedAF.IncontrasttoIART,theproportionofarrhythmiasduetoAF
decreased,withdiseasecomplexitylikely.Consideringtherelativelyyoungage
ofthefirstgenerationoflong-termsurvivorswithsurgicallypalliatedsevere
congenitalheartdisease,itisnotsurprisingthatolderpatientshavelesscomplex
disease.Thisislikelytochangeasthelifeexpectanciesofthemorecomplex
ACHDpopulationlengthen.
FocalAtrialTachycardia
Althoughincreasedautomaticityisthemostlikelymechanismoffocalatrial
tachycardia,othersincludetriggeredactivityandmicroreentry.Thetermfocal
atrialtachycardiaisusedinterchangeablywithatrialectopictachycardia,
althoughsomepreferadistinction.Focalatrialtachycardiaistheresultof
microreentryortriggeredmechanismsandisinduciblewithpacing.78Thereare
caseswherethistachycardiaisdistinguishedfromtheautomaticform;such
patientswereolderandmorelikelytohavecongenitalheartdisease.153Focal
atrialtachycardiaisusuallycharacterizedbywell-formedPwavesseparatedby
anisoelectricinterval,andelectrophysiologicallyithasacircumscribedoriginof
activationwithcentrifugalspread.Inpatientswithcongenitalheartdisease,focal
atrialtachycardiaspredominantlyariseinareasofabnormalconductionaround
suturepointsorscarborders.Theyareoftennonautomaticandarethoughttobe
duetomicroreentryowingtotheircapacitytobeinduced,terminated,and
entrainedbyprogrammedatrialstimulation.153Theseweretheleastcommon
arrhythmiasobservedinthemostrecentstudyofatrialarrhythmiasinACHD
patientsandpredominantlyoccurredinyoungpatients(meanage,24years)with
moderateorcomplexdefects.148
VentricularTachycardia
AlthoughventricularectopyandnonsustainedVTarerelativelycommon,
sustainedmonomorphicVTappearstobelesscommoninACHDpatients.44
ThisVTinACHDpatientscanbetracedtomyocardialchangesrelatedto
hemodynamicloading,cyanosis,orsurgicalinterventionsthatpredisposeto
arrhythmias.Researchershavelongsoughtpredictorsofsuddendeathinthis
populationandhaveconsideredinducibleVTasapotentialriskfactor.Although
thisisconcerning,aclearrelationshipbetweeninduciblesustained
monomorphicVTandanincreasedriskofsuddendeathhasnotbeenestablished
acrossallformsofcongenitalheartdisease.Therefore,intwoofthemost
commonlyfollowedACHDsubstrates,tetralogyofFallotandtranspositionof
thegreatarteriesmayhavedifferentriskfactorsforsuddencardiacdeath.There
isnosingularabsoluteriskfactorfortetralogyofFallot,butacompositerisk
scorehasbeenconsideredusinglaterepair,aQRSof180msormore,syncope,
priorshunt,andLVsystolicanddiastolicdysfunction.154Thismaybedifferent
thantranspositionofthegreatarterieswithMustardorSenningatrialbaffles,
where80%ofsuddendeathsoccurduringexerciseandischemiamayrelateto
rapidheartbeatsduringsinustachycardia/atrialarrhythmias,thusfosteringa
myocardial/oxygensupplymismatchtoanalreadyhypertrophicsystemicRV.155
DuetoahighburdenofscarintheRVOTofpatientsafterrepairoftetralogyof
Fallot,macroreentrantVTsarerelativelycommoninthispopulation.Giventhe
uncertainrelationshipbetweensustainedmonomorphicVTandsuddendeath
andtherelativelyhighriskofrecurrenceevenafteracutelysuccessfulablation,
VTablationisonlyrarelyandunderspecialcircumstancesseenasasubstitute
forICDtherapyandmostcommonlyasanadjunct.Thereforecatheterablation
canbehelpfulinreducingtheriskofrecurrentICDshocksand,muchmore
rarely,canbeperformedforhemodynamicriskinpatientswithslowbut
incessanttachycardias.44
