Andersons pediatric cardiology 556
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Sinusnodefunction:Thesinusnoderecoverytimeisameasurement
obtainedbyatrialpacingataconstantratefor30secondsandthenabruptly
terminatingpacing.Thetimetakenbythesinusnodetorecoveristhesinusnode
recoverytime.Sinusnodedysfunctionisuncommoninchildrenexceptafter
surgeryintheregionofthesinusnodeoritsbloodsupplyandrecordingsusing
eventmonitors,ambulatorymonitors,andexercisetestingmaybemoreuseful
forsinusnodeassessment.
AVnodalfunction:ThiscanbeassessedastheAHintervalinthebaseline
stateandastheeffectiverefractoryperiodduringextrastimulustesting(Fig.
22.26).AVnodalconductionisdecremental;thusitdiffersfromatrial,
ventricular,andaccessorypathwaytissueconduction.Withgraduallymorerapid
atrialpacing,AVnodalconductiontimeincreasesuntilthereisWenckebach
block.Age-relatednormalsexistforthesethreemeasures.Conductionacross
accessorypathwaysisusually“allornone”andthusconstantuntilblock.
FIG.22.26 Catheterelectrodespositionedinthehighrightatrium,right
ventricularapex,Hisbundle,andcoronarysinus.Therhythmexhibitedis
sinus,withbaselinePA,AH,andHVintervalsshown.CS,Coronarysinus;
HRA,highrightatrium;RV,rightventricle.
Tachycardiaassessment:Adetaileddiscussionofthisisbeyondthescopeof
thischapter,althoughsomedetailsareincludedinthesectiononthediagnosisof
tachycardia.AnimportantmaneuverintheSVTassessmentistheadministration
ofadenosineduringventricularpacing.Ifthereisevidenceofretrograde
conductionfromtheventricletotheatriumduringventricularpacing,this
conductioncanoccurovertheAVnode,overanaccessorypathway,ormayfuse
overthetwo.Theadministrationofadenosineduringventricularpacingresults
inAVnodalblockretrograde;thusifconductionpersists,itshouldbeconsidered
tobeoccurringoveranaccessorypathway.Additionally,tachycardiasthatcan
routinelybestartedandstoppedwithpacingareconsideredreentrant
tachycardias.Tachycardiainitiation(Fig.22.27)isimportantyetitcanbe
challengingpossiblyrelatedtotheadministrationofanesthesia.Isoproterenol
canbeusedtopotentiateconductionandmayallowtachycardiainitiation.This
maybeanimportantpartofaccessorypathwayfunctionalassessment.61
FIG.22.27 Inductionofatrioventricularnodalreentrytachycardiausinga
drivetrain(S1)andasingleatrialextrastimulus(S2).Thesolidbar
indicatesconductiondownthefastpathwayandthehollowbarindicates
conductiondowntheslowpathway.Duringthedrivetrain,conductionfrom
theatriumtotheHisbundleisviathefastpathway.Aftertheextrastimulus
(S2),thefastpathwayisblockedandconductionproceedsdowntheslow
pathwaytotheHisbundle(AHjump).Atthispointthefastpathwayhas
recoveredandconductsretrograde,sothattheAandVaresuperimposed
intheHisbundleelectrodeandaretrogradeAisdetectedinthehighright
atriumandcoronarysinusleads.Antegradeconductionisviatheslow
pathwayandareentrytachycardiafollows.CS,Coronarysinus;HRA,high
rightatrium;RV,rightventricle.
Mapping:Mappingcanbedoneinsinusrhythm,lookingfortheearliest
onsetofventricularactivationinapatientwithWPWsyndrome.Itcanbe
performedduringventricularpacing,lookingattheearliestsiteofatrial
activation,andcanhelpdifferentiateAVNRTfromAVRT.Mappingcanbe
undertakenduringSVT.ThisisespeciallyimportantinAVRT,asitallowsa
clearassessmentoftheearliestsiteofatrialactivation.MappingduringVToften
involvesidentifyinganintracardiacventricularelectrogramthatprecedesthe
surfaceQRScomplex(Fig.22.28).Pacemappingisperformedfortachycardia
assessmentandinvolvespacingfromventricularlocationsuntila12-lead
assessmentinpacingisidenticaltothe12-leadassessmentintachycardia.This
ismostoftenemployedforVTassessmentwhenthetachycardiaisnotsustained
orisnotwelltoleratedhemodynamically.Entrainmentmappingisusedinthe
settingofatrialorventricularreentrantcircuitswherethetachycardiacircuit
includesanareaofslowconduction.
FIG.22.28 Activationmappingofaleftfascicularventriculartachycardia.
Theearliestactivationontheablationelectrodeis64msaheadofthe
onsetoftheQRScomplexinanyofthesurfaceelectrocardiographicleads
atthesiteofsuccessfulablation.HRA,Highrightatrium;RV,right
ventricle.
Activationmapping:Duringectopictachycardias,acatheterismovedwithin
thechamberofinterestlookingfortheearliestintracardiacelectrogram.Thisisa
siteintheatriumortheventriclewherethetachycardiaoriginatesandisnotedto
precedetheonsetoftheactivityonthesurfaceECGPwaveinatrial
tachycardiasandtheRwaveinVTs.
Electroanatomicmapping:Theuseofelectronantomicmappingsystemshas
manybenefits(Fig.22.29).Thistechnologyhasnearlyeliminatedtheuseof
