Andersons pediatric cardiology 554
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basedstudies.Arapidincreaseintherateandspeed
(sprinttest)ofVTmaybemoreeffectiveat
uncoveringcatecholamine-provokedarrhythmias.
AdditionalTesting
Echocardiography.
Withregardtoarrhythmias,particularlyventriculararrhythmias,manydecisions
concerningmanagementandriskarebasedonwhetherthereisastructurallyand
functionallynormalheart;thusechocardiographicassessmentisimperative.The
Ebsteinmalformationorcongenitallycorrectedtranspositionofthegreatarteries
inwhichtherecanbeanEbstein-likemalformationofthesystemicAVvalveand
hypertrophiccardiomyopathyoccurinassociationwithWPWsyndrome.157
IncessantarrhythmiassuchasAET,JET,andPJRTcanresultinventricular
dysfunction;thereforeinitialandongoingechocardiographicassessmentis
indicatedinchildrenpresentingwiththesearrhythmias.Inadultswithahigh
burdenofventricularectopy,arrhythmia-inducedcardiomyopathyisdescribed
andcasesofthishavebeenreportedinchildren.Finally,inchildrenwith
congenitalheartdisease,theappearanceofarrhythmiasmaysuggestaworsening
ofthehemodynamicstatus,andechocardiographicassessmentiswarranted.
▪CardiacMRI:Certainconditionsarebestassessed
byMRI,includingARVCandmyocarditis,andthere
isincreasingevidenceoftheimportanceofMRIin
assessingforfibrosisinhypertrophiccardiomyopathy.
▪Laboratoryevaluations:Bloodchemistrytestingis
importantwhenQTprolongationisidentified,
especiallyifthereisnofamilyhistoryofLQTS,since
lowlevelsofpotassiumandmagnesiumcanresultin
QTprolongation.AtrialtachycardiasincludingAF
canbeseeninthesettingofhyperthyroidism.Finally,
serumdrugtestingshouldbeperformedinpatients
wheretheclinicalscenario,arrhythmias,andECG
seemconsistentwithanintentionaloraccidental
overdose,illicitdruguse,orchangesinrenal/hepatic
functionthatcouldaffecttheclearanceofprescription
medications.Mostantiarrhythmicagentshavethe
potentialtobeproarrhythmic;thus,inapatienttaking
theseagents,anewarrhythmiaorconductionchange
shouldpromptthetestingofbloodlevelswhen
possible.
ElectrophysiologicStudy
Althoughinitiallyconceivedasadiagnostictool,theEPSisnowperformed
mostlyinthesettingofacatheterablationprocedure.Manyofthediagnostic
portionsofthestudyarestillundertakeninthissetting.
TransesophagealElectrophysiologicStudy
Thisisalessinvasivetoolandmaybehelpfulinsituationswherediagnostic
informationisneededbutthechildistoosmallforaninvasivecatheter
procedureorinsituationswherethereisnotenoughinformationtomeritthe
study.Aspeciallydesignedbipolarcatheterisplacedinthenareswiththe
electrodetipintheregionoftheleftatrium.Electrogramsaresoughtwherethere
areatrialandventricularrecordingsbutonlyatrialpacingcanbeperformedwith
thistechnology.Atrialpacingisundertakentoinitiatetachycardia;assessatrial,
AVnodal,oraccessorypathwaycharacteristics;ortoterminatetachycardia.The
relationshipofatrialandventricularelectrogramsallowsforadeterminationof
associationordissociationbetweenthetwochambers.Studieshaveconfirmed
diagnosticaccuracy,similartothatofaninvasiveEPS.158Thisisalessinvasive
waytoprovideriskassessmentinchildrenwithasymptomaticWPW
syndrome.159
InvasiveElectrophysiologicStudy
Procedure
Anesthesia.
MostpediatricEPSsareundertakeninassociationwithacatheterablation;in
thissetting,generalanesthesiaisoftenused,butthereisatrendtowardavoiding
inhalationalanesthetics.Propofolismostcommonlyused.Anesthesiaminimizes
discomfort,decreasesmemoryoftheprocedure,anddecreasesmovementduring
theprocedureforgreatersafety.160However,ifablationisnotanticipatedand
theprocedureislikelytobeshort,conscioussedationmaybeadequate,
dependingonthepatientandthelaboratoryexperience.Adultproceduresare
oftendonewithsedationratherthananesthesia,andtheoriginalrisk
stratificationstudiesinWPWsyndromewereperformedwithoutanesthesia.50
Thereareconcernsabouttheeffectsofanesthesiaonmyocardialtissue
conductionandrefractoriness.Studieshaveshownthatneitherpropofolnor
isofluraneanesthesiaalteredsinuatrialorAVnodefunctioninpediatricpatients
undergoingRFcatheterablation161andthatintravenousanesthesiahadnoeffect
onarrhythmiainductionorslow-pathwayablationinpatientswithdocumented
AVnodalreentranttachycardia(AVNRT).162Furthermore,propofolhasnot
shownaclinicallysignificanteffectonaccessorypathwaycharacteristics.163
Catheters.
Thereareavarietyofmultipolecathetersthatallowpacingandsensingandcan
beplacedinanychamber,althoughthestandardapproachisplacementinthe
highrightatrium,rightventricularapex,andthroughtheanterosuperiorpartof
thetricuspidvalvetorecordelectricalactivityfromtheHisbundle(Fig.22.25).
Thesesitesareusuallyaccessedfromafemoralvenousapproach.Whencatheter
ablationisplanned,amultipolecatheterisplacedinthecoronarysinustorecord
atrialandventricularelectrogramsfromtheleftAVgroove,usuallyaccessed
fromsubclavianorjugularvenousapproach.Cathetersarenotplacedintheleft
ventricleorleftatriumunlessindicatedbythetachycardiasubstrate.TheRV
apicalcathetercanberepositionedintheRVOTforventricularstimulation
studies.
