Andersons pediatric cardiology 1912

entrypointoftheisthmus.Theseareasofslowconductionusuallydevelop
aroundareasofscareithersurgicalorduetoprogressiveatrialfibrosis(Fig.
73.16).AfterallformsofFontan,thecommonestpositionforsuchanisthmusis
betweenthebottomendofarightatriotomyscarandtheinferiorvenacava
(“pericavalorigin”).116Thisisdifferenttootherpostoperativecongenitalheart
groupsandthestructurallynormalheartwithatrialflutter,wheretheisthmus
commonlyrunsacrosstheanatomiccavotricuspidjunction.Ithasbeenproposed
thatanadditionalsurgicallineshouldbemadeatthetimeofthelateraltunnel
surgery,topreventsuchanisthmusdeveloping.Unfortunately,giventhetime
laginthedevelopmentofIARTaftertheFontanprocedure,itwillbedecades
beforeweknowifthishasbeensuccessful.117Asmentionedbefore,some
modifiablesurgicaltechniquesmayhelptopreventIART.Certainly,themove
awayfromatriopulmonaryconnectionhasbeenbeneficial,ashasreducedageat
thetimeoftheFontanoperation.

FIG.73.16 Ananteroposteriorprojectionofathree-dimensional
electroanatomicmapinapatientwithintraatrialreentranttachycardia
(IART)postFontan.ThewhitearrowsshowtheIARTcircuit,withthe
criticalzonelocatedinagapinascar(grayareas)onthelateralwall.The
intracardiacsignalstakenatthiszone(bluearrows)showlong,lowvoltage,fractionatedsignals.Asingleradiofrequencylesioninthatarea
interruptedthetachycardia.

Othercongenitalarrhythmiasubstratessuchasaccessorypathway–mediated


tachycardiasandatrioventricularnodalreentranttachycardiasaccountforupto
30%ofthetachycardiasinFontanpatientstreatedinatertiaryelectrophysiology
laboratory.115Thesetachycardiasaremoreresponsivetomedicalandablative
therapythanIART.
Intheacutesetting,medicalmanagementcanbedifficult,andthepatientmay
havedecompensatedcardiacfailure,asbothacauseandeffectoftheIART.

Directcurrentcardioversioncanfailinaquarterofpatients,withincreased
successrateiftypeIorIIIantiarrhythmicmedicationsarestartedprior.118
Medicationforratecontrolcanbedifficulttomanagebecauseofthecommonly
associatedsinusnodedysfunction,andalthoughamiodaronecanbeeffective,
sideeffectscanbeharmfulwhenthismedicationisusedlongterm.Thus,inthe
adultpatientwithanatriopulmonaryconnection,medicalmanagementis
frequentlyunsuccessful.Interventionalstrategiesinvolveachoiceof(or
combinationof)acatheterablationstrategyversusasurgicaltakedowntoa
lateraltunnelorextracardiacconduitwithconcomitantsurgicalablation
techniques,usuallyamazeprocedure.
CatheterablationforIARTintheatriopulmonaryFontancanbesuccessfulin
theshortterm,butthereisahighrecurrencerate.119Thisisnotsurprisinggiven
thefactthattheunderlyingsubstrate—theatrialdilationandwallthickening
withlargeareasofscarredandelectricallyinhomogeneoustissue—isnotaltered.
Thegrosslydilatedatriumisalsoanidusforthrombusformationandis
hemodynamicallyinefficient.TheearlyFontanconversionexperiencewasone
ofconsiderablemortalityoutsideofseveralhigh-volumecenters.Theresultsof
thissurgeryareimproving,andthisimprovementrelatesatleastinparttoa
betterappreciationoftheindicationsforoperation.107,120Manycentershave
publishedfavorableresults,withanearlymortalityrateofapproximately5%,
improvedNYHAfunctionalclass,andreductioninarrhythmiaincidenceover10
years(seelater,“SurgicalManagementofFontanFailure”).121–124

AtrialFibrillation
AtrialfibrillationcommonlyoccursearlierintheFontanpopulationthaninother
patientswithpostoperativecongenitalheartdiseaseandisgenerallypoorly
tolerated.Onsetoftenoccursinthethirddecade,usuallyasanintermittent
arrhythmiathatcommonlycoexistsoralternateswithotheratrialtachycardias.
Progressiontosustainedatrialfibrillationiscommonwithin5yearsofthefirst
episode.Theinclusionofleftatrial(Cox)mazewithrightatrialmazeatthetime

ofFontanconversionmayproveeffectiveinreducingtherecurrencerateofthis
arrhythmia,especiallyinolderpatientsandthosewhoalreadyhaveatrial
fibrillation.However,itisnotknownwhatproportionofatrialfibrillationhasa
leftatrial/pulmonaryveinoriginintheFontancirculation,eventhoughthisisthe
commonestmechanisminthestructurallynormalheart.Thereisanecdotal
evidence,anditmakesintuitivesense,thatsomeatrialfibrillationinthese
patientshasarightatrialorigin.125

RoleofCatheterAblation
Althoughasurgicalapproachmaybemostappropriateforthosewithatrial
tachycardiawithanatriopulmonaryFontan,catheterablationhasaroleinother
cases.Anablationcanbeausefulpalliationwhereconversioniscontraindicated,
atrialdilationisnotexcessive,orthepatienthasdeclinedsurgery.Focalatrial
tachycardiascanberelativelystraightforwardtoablate,alongwithcongenital
arrhythmiasuchasaccessorypathways,atrioventricularnodereentrant
tachycardia,andrarecaseswithtwinatrioventricularnodes.115Withthe
extracardiacconduitorlateraltunnelFontan,thecriticalisthmusisusuallyon
thecardiacsideofthebaffle,sothataccessforablationcathetersisdifficult.
However,therehasbeenincreasingconfidenceintheuseoftransbafflepuncture
techniqueinthesecasesbecausethereiscommonlyasafepuncturepointatthe
lowerendofthebaffleatthejunctionwiththeinferiorvenacava/atrial
border.126