Andersons pediatric cardiology 566
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compatibilitymustbedetermined.Otherfeaturestoevaluatearethedifferent
programmableoptions,includingautomaticcapture,atrialtherapies,size,and
batterycapacity.Variousleadcharacteristicsincludediameter,polarity,
insulationmaterial,andfixationmechanism.Thefamily'sabilitytosendremote
monitoringforsurveillancepurposesisimportanttoassess.
EpicardialVersusEndocardialImplantation
Pacingleadsarerecognizedasthemostvulnerableandproblematiccomponents
ofthepacemakersystem.Factorssuchasthepatient'sgrowth,uniqueanatomy,
scar,needforlifelongpacing,activitylevelofthechild,andthelong-term
vascularaccessissuesincreasethesusceptibilitytoleaddamage.Earlier
epicardialleadswiththescrew-inmechanismresultedinacuteinflammationand
subsequentscarringatthemyocardialinterface.Newersteroid-elutingleads
havearesponsecomparabletothatofendocardialleads.Epicardialsystemsin
theacuteperiodhaveahigherincidenceofdevelopingpericardialeffusionor
postpericardiotomysyndrome.Theriskofsubclavianorinnominatevein
thrombosiscommonlyparallelsthevesselsizeatinitialimplant.Studieshave
soughttodefineriskfactorsforvenousobstruction.196Initially,calculations
relatinghardwaretobodysurfaceareawereused.Morerecentstudieshavenot
correlatedageatimplant,bodysurfacearea,priorheartsurgeries,leadduration,
numberofprocedures,orleadindextobestatisticallysignificant.197Preserving
long-termvesselpatencyforthepossibleneedtoaddanadditionalleadorlead
extractioninthefuturecanbedifficultinanalreadychallengingpopulation.
UnipolarVersusBipolarLeads
Unipolarandbipolarpacingsystemshavebeenusedsincethefirstdecadeof
cardiacpacing.Bothpermitelectricitytoflowfromonepoletotheotherand
deliveranelectricalcharge.Aunipolarleadisasingle-conductorleadwithan
electrodelocatedatthetip.Thereforetheelectricalcircuitisdependentonthe
singleelectrodeleadtothegeneratorandmyocardium.Thebenefitsofunipolar
systemsarethattheleadsaresmallerindiameterandhavemoreflexibility.
Disadvantagesarelowerimpedance,ashorterbatterylife,anincreasein
oversensingextracardiacsignals,skeletalmusclepacing,andnotasmuch
flexibilityifanyinsulationdamagetotheleadarises.Abipolarleadhastwo
separateisolatedconductorswithinasinglelead;thedistalelectrodeisatthattip
andtheproximalelectrodeabout2cmproximaltothetip.Itisimportantto
rememberthatbipolarsystemsdonotalwaysdemonstratepacingspikesona
surfaceECGandcanmakeinterpretinganECGmorechallenging.Inabipolar
system,ifthereisdiscreteleaddamage,thereistheoptionofreprogrammingthe
devicetoaunipolarsystemandpossiblymaintainingadequatesensingand
thresholds.
CongenitalHeartDisease
Patientswithcomplexcongenitalheartdiseasewilllikelyhavemultipleopenheartoperationsoverthecourseoftheirlives.Asaresult,patientshave
myocardialscarringthatcreateschallengesforoptimumleadplacementand
performance.Surgicalpalliationsinthecongenitalheartdiseasepopulation
produceuniqueinterventionsandleadplacementapproaches,asseeninthe
single-ventricleandatrial-switchpopulation.Epicardialdevicesareroutinely
usedinsmallchildrenaswellaspatientswithintracardiacshunts,prosthetic
tricuspidvalves,orchambersthatcannotbereadilyaccessedfromthe
vasculature.Asaresult,epicardialleadsareoftenrequired.Thedecisionasto
whichleadorleadsandwhichchambershouldbethoughtfullydiscussedwith
thecardiacsurgeonpriortoproceedingtotheoperatingtheater.An
understandingoftheanatomyprior,surgicalapproaches,andechocardiographic
areasofdyssynchronyshouldbecollectivelydiscussedsoastooptimizelead
durabilityandleadintegrityandtooptimizehemodynamicsforparticular
patients.Studieshavebeenperformedtoidentifythelifespanofepicardial
systemsgiventheseconcernsandfoundtheleadsurvivaltobeacceptable.198
Patientswithtransvenoussystemsandthepresenceofanintracardiacshuntare
atagreaterthantwofoldincreasedriskofpulmonaryemboliorsystemic
embolicevents.199Theapproachtothepatientwithuniventricularpalliation
variesbetweencentersandoperators,withmostutilizingepicardialsystemsin
thispopulation.
PacemakerInfection
Inhealthypatientswithimplanteddevices,therecentguidelinesfromthe
AmericanHeartAssociationforthepreventionofbacterialendocarditisdonot
recommendantibioticprophylaxis.Riskfactorsforthedevelopmentofdeeppocketinfectionsincludereoperationandtrisomy21.200Superficialinfections
shouldbefollowedcloselytoidentifyifthereisprogressiontoadeep-pocket
infection.Oncesuchaninfectionhasoccurred,theentirehardwaresystemmust
beremoved.Signsandsymptomsofinfectioncanbeskinbreakdownatthe
incisionsite,anelevatedwhitecellcount,fever,malaise,localizededema,
increasingerythema,anincreaseinwarmthattheincision,discharge,wound
dehiscence,and/orpain.Themostcommonorganismsidentifiedindevice
infectionsaregram-positivebacteriafoundinstaphylococcalinfections.Gramnegativebacteriaaccountsforfewerthan18%ofinfections,andabout15%of
deviceinfectionsareculture-negative.Ifapatientispacemaker-dependent,often
atemporaryleadcanbeplacedataremotesitewhiletheappropriateantibiotics
aregivenandthedeviceandleadsareremoved.Iftheleadsarechronicand
likelynoteasilyremovable,considerationforamoreinvasiveleadextraction
shouldbeentertained.Transvenousleadextractionsarehigh-riskproceduresand
shouldbeperformedatacenterwithreadilyavailablesurgicalexpertise.Recent
guidelineshavebeenpublishedregardingleadextractioninchildrenand
adults.200
DualVersusSingle-ChamberDevices
Majortrialshavebeenperformedinadultpopulationstoidentifythevalueof
single-versusdual-chamberdevices.Therationalefordual-chambersystemsis
topreserveAVsynchronyandsubsequentlypreservemyocardialfunction.The
benefitsofdual-chamberpacingtopromoteAVsynchronyhavebeenwell
defined;however,thereisevidencetosupportminimizingventricularpacing.
ProgrammingafixedlongAVdelaymayminimizeventricularpacingbutis
sometimesnotfeasible.Inthepediatricandcongenitalheartdiseasepopulation
decisionsareoftendrivenbypatientsizeandanatomy.Theyoungerpatientswill
oftenbegivenaninitialsingle-chambersystemthatislaterupgradedtoadualchambersystematdevicerevision.Abiventricularpacingsystemmaybe
recommendedinpatientswithimpairedLVfunctionwhorequirepermanent
pacing.
LeadlessPacing
Leadfailureisacommoncomplicationofpacemakerplacementinthepediatric
populationandisoftenduetoinsulationbreaks,leadfracture,dislodgement,an
increasedriskforinfection,andvascularocclusion.Theseconsequencescan
