Andersons pediatric cardiology 558
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FIG.22.31 Electroanatomicmappingofafocalatrialtachycardiaina14year-oldboyduringradiofrequencyapplication.Thefirstthreebeatsonthe
tracingsrevealanectopicatrialtachycardia.ThePwaveisinvertedinlead
I(thickyellowarrow).Theablationcatheterispositionedatthebaseofthe
leftatrialappendage.Withradiofrequencyenergy,thefocalatrial
tachycardiaterminatestosinusrhythm(uprightPwaveinleadI,thinyellow
arrow).
Ablationinchildrenhasbeenperformedsincetheearly1990s;itsefficacy
wasinitiallyassessedinthemulticenterdatafromthePediatric
ElectrophysiologyCatheterAblationRegistryreportedin1994fromthe
PediatricElectrophysiologySociety.163In2000,datawereprospectively
collectedaspartoftheProspectiveAssessmentafterPediatricCardiacAblation
studyforRFablation.164Over2700patientsfrom41centerswereprospectively
enrolled,ofwhom481followedastandardprotocolforaperiodof2years.The
initialsuccessrateforallSVTsubstrateswas93%andforVT78%.Recurrence
wasrelatedtosubstrateandwashighestforright-sidedaccessorypathways
comparedwithleft-sidedpathways.165Itisimportantthatpriortoembarkingon
catheterablation,theoperatorclearlyunderstandthearrhythmicsubstrateandits
locationrelativetonormalanatomicstructuresincludingtheAVnode,His
bundle,bundlebranches,AVvalves,andcoronaryarteries.Majorcomplications
arerareandrelatedtounderlyingheartdisease,lowerpatientweight,greater
numberofRFapplications,andleft-sidedprocedures.166Themostcommon
seriouscomplicationswereAVblock(secondand/orthirddegree),catheter
perforationorpericardialeffusion,andthrombioremboli.
Overthelast15yearscryoablationhasbecomemorewidelyused,especially
whentheareaofinteresttobeablatedisincloseproximitytothenormalAV
nodal/Hisconductioncircuit.Cryoablationofferstheadvantageofpotentially
reversiblelesions,thusreducingtheriskofpermanentheartblockorother
undesirabletissueeffects.MostlaboratoriesnowhavebothRFandcryoablation
availableandtailortheusageofeachtotheindividualpatient.
Mostarrhythmiasubstratesthatoccurinthepediatricpopulationareamenable
tocatheterablation.Anexpertconsensusstatementconcerningablationin
childrenandthosewithcongenitalheartdiseasewasrecentlypublishedand
outlinessuccessratesandcomplicationsoftheprocedureinthispopulation.167
Therearenoregistryorprospectivetrialdatadetailingtheuseofcryoablation
inthepediatricpopulation.Althoughpermanentfirst-degreeAVblockhasbeen
described,higher-gradeAVblockrequiringpacemakerimplantationhasnotbeen
reported.168Theriskofcoronaryinjuryisthoughttobelowerwithcryoablation.
Manycentersthatperformablationinchildrenhavetheabilitytoperformthe
procedurewitheitherRFenergyorcryothermalenergy,andthechoiceofwhich
modalityuseddependsonarrhythmiasubstrateandlocationandoperator
preference.TheoutcomedifferencesbetweenRFandcryoablationarethoughtto
beminimal.Therecommendationsfromtheexpertconsensusdocumentstates
thatisreasonableforcryotherapytobeanavailableoptionatcentersperforming
pediatricablations.
Routineperformanceofcatheterablationofininfants(≤1yearofage)and
smallchildren(≤15kg)iscontroversialandreservedforthosewhoareintolerant
ofthearrhythmiaandinwhomaggressivemedicalmanagementisineffective.169
SomeanimalstudiessuggestthatbothRFandcryoablationlesionsinyoung
childrenmaygrowaftertheprocedure,buthumandataarelacking.170,171
Symptomaticarrhythmiasarecommoninpatientswithcongenitalheart
disease,withaprevalencethatincreaseswithage,anatomiccomplexityand
surgicalburden.Inthispopulation,arrhythmiasarenotonlymoreprevalentbut
alsooftenmoresymptomaticandchallengingtotreatwithmedicaltherapy.As
thepatientwithcongenitalheartdiseaseages,mostofthearrhythmia
mechanismsareduetomacroreentryandassuchareamenabletocatheter
ablation.Theseareoftencomplexproceduresandtheablationteamneedsa
detailedunderstandingoftheanatomyandprevioussurgicalinterventions.
Sometimesthechamberofinterestisdifficulttoapproachandtechniquessuch
astranshepaticcatheterizationandtheabilitytopunctureabaffleshouldbein
thearmamentariumoftheoperator.Surgicalscarsandatrialandventricular
myocardialthickeningmaynecessitatetransmurallesionssometimesatdepths
greaterthan1cm.Insuchcases,RFenergydeliveredthroughactivelyor
passivelycooledtipsisgenerallyuseful,resultinginhigherpowerdelivery,
largerlesionvolume,andgreateracuteandlong-termsuccessrates.172,173The
generalavailabilityofadvancedmappingsystemsthatdonotrelyon
fluoroscopyhasledtoareductionintheradiationexposureforpatientsand
electrophysiologylabstaff.Thistechnologyhasadvancedtheabilityto
characterizeabnormalcardiacanatomyandlocatearrhythmiasubstratesin
childrenandACHD,andinmanylabsthisisaccomplishedwithzero
fluoroscopy.
