Andersons pediatric cardiology 562
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FIG.22.33 Dual-chamberimplantablecardioverter/defibrillator.Thetop
channelistheatrialelectrogram.Thesecondchannelistheventricular
electrogram.Thesixthventricularbeatoccursontopofthesinus
ventricularcomplex,resultinginpolymorphicventriculartachycardia.20J
ofenergydeliveredatthebottomtracingshowsconversiontosinus
rhythm.
CardiacResynchronizationTherapy
Morethan70%ofcardiacresynchronizationtherapy(CRT)casesinpediatricsis
undertakenincongenitalheartdiseasepatientswhohavenotrespondedto
maximalmedicaltherapy(Fig.22.34).CRTcanresultintheimprovementin
heartfailuresymptoms,reducedmorbidity,mortality,andanimprovedqualityof
lifeinpatientswithNewYorkHeartAssociationfunctionalclassIII/IV.Itcan
resultinimprovedejectionfraction,reducedleftventricleremodelingand
reducedmitralregurgitation.181ThegoalofCRTistorestoremyocardial
functionbyreestablishingcardiacsynchronyattheAV,interventricular,and
intraventricularlevels;thisiseffectiveinabouttwo-thirdsofpatients.
Diminishedcardiacoutputmayoccurinpatientswithaleft-bundle-branch-block
patternonECG,whichresultsindelayeddepolarizationofthelateralLV
wall.191Long-termRVpacinghasbeenanidentifiedriskfactorforsymptomatic
dyssynchronyandisgreatestamongyoungerpatientswhoareexposedto
ventricularpacingformanydecades.StudieshavesuggestedthatchronicRV
apicalpacinginyoungpatients,primarilythosewithcongenitalcompleteheart
block,canleadtoadversehistologicchanges,ventriculardilation,and
dysfunction.
FIG.22.34 Ananteroposteriorchestradiographofaninfantwith
congenitalcompleteheartblockandadilatedcardiomyopathy.Thepacing
leadsareepicardialandconnectedtoacardiacresynchronizationtherapy
deviceintheabdomen.
Mostadultresynchronizationproceduresareperformedbytransvenously
placingtheLVleadviathecoronarysinusintoalateralcardiacveinandonthe
epicardialLVsurface.Thisistechnicallymorechallenginginpediatricand
congenitalheartdiseasepatients,andthereareincreasedrisks.Biventricular
pacingsystemsinpediatricpatientscommonlyinvolveamediansternotomyor
thoracotomyforproperplacementoftheLVlead.
PriortoconsiderationofaCRTdevice,adetailedassessmentofthepatient's
priordevicetherapy,pathology,cardiacconductionabnormalities,anddegreeof
heartfailuremustbeperformed.Toidentifycandidatesinwhomtherapywould
bemostsuccessful,itisbesttoidentifytheLVleadposition,myocardialscar
distribution,etiologyofsystolicdysfunction,percentageofbiventricularpacing,
lackofmechanicaldyssynchrony,andQRSmorphologyandduration.
Todate,outcomesofCRTinpediatricandcongenitalheartdiseasepatients
arelimitedtotwomulticenterstudiesandonesingle-centerstudy.Findings
rangedfrom10.7%to18.5%nonresponderswithcomplicationsin9.2%to29%
ofpatients.192–194CRTpromotesanincreaseinstrokevolume,stabilizesthe
diastolicfillingtime,anddiminishesmitralregurgitationwithfavorable
outcomesinpediatricandcongenitalheartdiseasepatientsthatarenotdissimilar
