Andersons pediatric cardiology 559
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PacemakersandDefibrillators
HistoryofCardiacElectricalDevices
Devicetherapyandcardiacpacinghavealongandcolorfulhistory.Themoderndayimplantablecardiacelectronicdevicesbecamepossiblethrougha
combinationofnecessity,tenacity,andingenuityalongsideadvancesinanatomy,
pathophysiology,cardiacsurgery,andelectricalengineering.Whereasscientists
havebeenfascinatedwithelectricityforcenturies,itwasMarkLidwell,an
Australiananesthetist,whoin1929presentedthefirstartificialpacemaker.
Usingaunipolarneedleelectrodeinserteddirectlyintotheheartandan
indifferentplateelectrodesoakedinconcentratedsalinesolutionontheskin,
Lidwellranpulseventricularstimulationat16Vforaperiodof10minutes,after
whichthebabysurvived.174Approximately25yearslater,inanepochalpaper,
PaulZolldescribedcardiacresuscitationviaelectrodesplacedonthepatient's
barechestwith2-mspulsedurationsof100to150Vacrossthechest,sparking
widespreadmediaattention.175Fouryearslater,in1956,Zollpublishedhis
accountoftranscutaneouslyterminatingVF.175,176
In1954,C.WaltonLilleheiforeverchangedthelandscapeofpediatric
cardiologyandcardiacsurgerybysuccessfullyclosingaventricularseptaldefect
usingcrosscirculation.177Althoughclosureoftheseptaldefectprovedtobe
successful,injurytothecardiacconductiontissueresultedinsignificant
morbidityandmortality.Lilleheifirstuseddirectmyocardialstimulationfroman
externalpacemakerpoweredbyalternatingcurrent.However,inOctober1957,a
majorpoweroutageoccurredinMinneapolisthatlastedmorethan2hours.
WhiletheUniversityofMinnesotaHospitalhadanauxiliarypowersupply,
LilleheiwasconcernedaboutthepluginhisGrassphysiologicstimulator.This
concerncombinedwiththelackofalong-termsolutionandthepoorresultswith
chronicrectalisoproterenolmovedLilleheitoapproachEarlBakken,ayoung
electronictechnicianatthehospital,forasolution.Bakkenrecalledanarticlehe
hadreadinApril1956inPopularElectronicsinwhichthecircuitryforan
electronicmetronomewasdescribedusinga9-Vbatteryalongwithtwo
transistorsandanoscillatingtransformer.Within1month,Bakkenoffered
Lilleheiawearablebattery-operatedpacemaker.178,179
In1958,ÅkeSenning,athoracicsurgeonattheKarolinskaHospitalin
Stockholm,implantedthefirstinternalpacemakerusingmyocardialelectrodes
andarechargeablenickel-cadmiumbattery.Althoughthepulsegeneratorfailed
withinafewhours,asubsequentgeneratorlastedabout6weeks.Twoyears,
laterWilliamChardack,ChiefofThoracicSurgeryattheVeteran's
AdministrationHospitalinBuffalo,NewYork,workingwithengineerWilson
Greatbach,carriedoutthefirstsuccessfulimplantationofabattery-powered
generator.180Theinitialpacemakersofthe1960shavelittleresemblancetoour
currentdevices.Thepacemakersofthe1960swerepoweredbyzinc–mercuric
oxidecellsandfunctionedsolelyinanasynchronousVOOmodeatafixednoprogrammableratewithcompletedisregardforanyintrinsicelectricalactivity.
Bypacinginanasynchronousmode,therewasalwaystheconcernthatanilltimedpacedbeatcouldinduceVF.Mostoftheinitialpacemakerswereplaced
forindividualshavingexperiencedlife-threateningStokes-Adamsattacks,and
allrequiredathoracotomy;moreover,leadsfrequentlyfractured,necessitating
multiplethoracicprocedures.Asphysiciansworkedwithengineersatdevice
companiesinthe1960s,additionalmajoradvancementsincludedthecreationof
lithiumbatteries,transvenouspacingleads,andpacemakersthatsensedintrinsic
cardiacdepolarizations.The1970sandearly1980switnessedthedevelopment
ofdual-chambereddevicesandprogrammablepacemakerswherebythe
physiciancouldnoninvasivelyadjustthepacemakersettingsusingaprogrammer
thattransmittedcodedinstructionsonacarriersignalthroughthepatient'schest
totheimplantedpulsegenerator.Theintegrationofthesetwofeatures
revolutionizedthefieldofpacing.181Thenextgenerationsofpacemakerswere
capableofprovidingrate-responsefeaturesforindividualswithchronotropic
incompetenceandantitachycardiameasurestoaddresscertainarrhythmias.The
latestadvancementofbiventricularpacingcombinedwithcontemporaryheart
failuremanagementhasimprovedthelivesofmanypatientswith
cardiomyopathiesandventriculardysfunction.
AntibradycardiaPacing
Thedecisiontoplaceapermanentpacemakermaynotalwaysbecompletely
straightforward,especiallyinpediatricpatientsandthosewithcongenitalheart
disease.Evidence-basedguidelinesforprescribingantibradycardiapacinghave
beenwellvettedandpublishedbyanumberofNorthAmericanandEuropean
cardiacsocieties,includingtheAmericanHeartAssociation:
www.americanheart.org;theAmericanCollegeofCardiology:www.acc.org;the
HeartRhythmSociety:www.hrsonline.org;andtheEuropeanHeartRhythm
Society:www.escardio.org.
GuidelinesforPacemakerImplantation
Pacemakerimplantationguidelinesforchildren,adolescents,andpatientswith
congenitalheartdiseaseareoutlinedandspecificsituationsarediscussed
hereafter.Itisworthnotingthatthereareoftenslightvariationsbetween
recommendationsoriginatingfromNorthAmerica,Europe,andAsia.24,182
RecentguidelineshavealsobeenpublishedfordeviceimplantationinACHD.44
Whereasguidelinesarehelpfulinprovidingacontextwithwhichtoplacea
pacemaker,allcasesshouldbeindividualized.
ClassI(thereisevidenceand/orgeneralagreementthatpacingisbeneficial,
useful,andeffective):
1.Advancedsecond-orthird-degreeAVblockassociatedwith
symptomaticbradycardia,ventriculardysfunction,orlowcardiac
output.
2.Sinusnodedysfunctionwithcorrelationofsymptomsduringageinappropriatebradycardia.Thedefinitionofbradycardiavarieswiththe
patient'sageandheartrate.
3.Postoperativesecond-orthird-degreeAVblockthatisnotexpectedto
resolveorthatpersistsatleast7daysaftercardiacsurgery.
4.Congenitalthird-degreeAVblockwithawideQRSescaperhythm,
complexventricularectopy,orventriculardysfunction.
5.Congenitalthird-degreeAVblockinaninfantwithaventricularrateless
than55beats/minorwithcongenitalheartdiseaseandaventricularrate
lessthan70beats/min.
ClassII(thereisconflictingevidenceand/ordivergenceofopinionaboutthe
usefulness/efficacyofthegiventreatmentorprocedure)
ClassIIA(theweightofevidence/opinionisinfavorofpacing):
1.Congenitalheartdiseaseandsinusbradycardiaforthepreventionof
recurrentepisodesofintraatrialreentranttachycardia;sinusnode
dysfunctionmaybeintrinsicorsecondarytoantiarrhythmictherapy.
2.Congenitalthird-degreeAVblockbeyondthefirstyearoflifewithan
