Andersons pediatric cardiology 1652
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outcomes.248,249Cardiopulmonaryexercisetestingmayalsoidentifyablunted
bloodpressureresponse(≤20mmHgincreaseinsystolicbloodpressure)to
exercise,whichhelpstostratifypatientsatriskforsuddendeath.250,251Exercise
testingisalsoreasonablefortheevaluationofexercise-inducedLVOTOwhen
therestingpeakgradientisbelow50mmHg.
Management
GeneticTestingandDiseaseScreening
TheimprovementinHCMovertimeismultifactorial,butimprovedscreeningis
likelycontributory.PatientsatriskforthedevelopmentofHCMshouldreceive
routineECGandechocardiographicscreening.Ascreening12-leadECGand
echocardiographyarecurrentlyrecommendedevery12to18monthsinchildren
andadolescentsandevery5yearsinadults(typically18to21yearsofage,
whenphysicalmaturityreached).Geneticcounselingisalsorecommendedfor
allpatientsindependentlyofwhethersuchtestingwillbeusedtohelpwith
screening.6,7
TreatmentofSymptomaticLeftVentricular
OutflowTractObstruction
Thecurrentguidelinesrecommendtheinitiationofmedicaltherapyinthesetting
ofLVOTO(≥30mmHg)andsymptoms.6Somecentershavetakenamore
prophylacticapproach,especiallyinyoungerchildren,wheresubjective
assessmentofsymptomsisdifficultandcoordinationprecludesobjective
assessment.234Itisunclearifthesurvivaladvantagereportedfromtheuseof
veryhighdoseβ-blockertherapy(>20mg/kgperday)atasinglecenteris
broadlyapplicable.252
First-linetherapyforsymptomaticpatientswithrestingorprovocableLVOTO
consistsofnonvasodilatingβ-blockertherapy(1to2mg/kgperday)(atenolol,
metoprolol,nadolol,bisoprolol).Ifβ-blockertherapyisunsuccessfulinreducing
symptoms,verapamilmaybeinitiated(2to7mg/kgperdayupto480mg/din
adolescents/adults).Disopyramidemayalsobeaddedinconjunctionwitheither
aβ-blockerorcalciumchannelblockertoimprovesymptoms.Disopyramide
shouldalwaysbeusedinconjunctionwithatleastonerate-controllingagentdue
tothepotentialforenhancedatrioventricularconductionduringatrial
arrhythmias.253
Patientswithresidualsymptomsinspiteofoptimalmedicaltherapyorwho
cannottoleratetherapymaybecandidatesforsurgicalmyectomy.254In
experiencedhands,septalmyectomycanbeperformedwithminimalmortality
inadults,althoughthereisariskforrepeatmyectomyduetorecurrentor
residualLVOTO.255Inadditiontoreoperation,thereisalsoariskofaorticvalve
injury,mitralvalveinjury,ventricularseptaldefect,andatrioventricularblock.255
Theriskofthesecomplicationsislikelyhigherinsmallerpatientswherethereis
limitedexposureviatheaorticannulus.Consequentlythepreciseroleof
myectomyinchildrenremainstobedetermined.
Dual-chamber(atrioventricular)pacingwithoptimizedarteriovenousdelay
hasalsobeenusedasatherapyinpatientswithrecalcitrantsymptoms;however,
randomizedtrialsexploringthebenefitsofthisapproachsuggeststhataplacebo
effectmayhavedriventheinitialresults.256,257Theremaybesomebenefitto
pacinginolderpatientsandthosewithunderlyingconductiondisease;however,
thistopicisnotyetresolved.Alcoholseptalablationmayalsobeareasonable
approachtomyectomyinselectedadultpatients;however,thisapproachisnot
recommendedinpediatrics.6,7,258
SymptomaticNonobstructiveDisease
HCMwasfirstdescribedasadiseaseofLVOTduetoasymmetrichypertrophy
oftheseptum.9,12,13,47,213Thisisreflectedintheearlynamesforthedisease
(e.g.,idiopathicsubaorticstenosis)andthelackofearlystudiesonpatientswith
nonobstructiveHCM.Theearlynamespersistedforatimedespitethefactthat
someone-thirdofreferral-basedadultpatientshavenonobstructivediseaseand
themajorityofpediatricandyoungadultpatientshavenonobstructive
disease.34–36,224Patientswithnonobstructivediseaseappeartohaveamore
benignprognosisversuspatientswithobstruction;however,thereisaresidual
riskforsymptomaticdiseaseanddisease-relatedcomplications.224
Whenassessingsymptomsinpatientswithnonobstructivedisease,itis
importanttoassessforinducibleobstruction.Infact,theproportionof
pediatric/youngadultpatientswithinducibleoutflowtractobstructionmaybe
higherthanthatofthosewithobstructionatrest.36Therapyislimitedandis
similartothetreatmentofpatientswithobstruction(β-blocker,calciumchannel
blocker,anddisopyramidetherapy).
PreventionofSuddenDeath
Theoverallriskofsuddendeathinthecurrenteraisabout0.5%/year.Although
therehavebeenclinicalgainsindecreasingtherateofsuddendeathinthe
population,childrenandyoungadultswithasymptomaticormildlysymptomatic
diseaseareamongthehighest-riskpopulations.34,35Someoftherisk
traditionallyassociatedwiththispopulationappearstobemodifiablewith
improvedscreeningandcontemporaryICDtherapy.36,231,259
Suddendeathisthoughttoresultfromventriculararrhythmiasecondarytoa
combinationofmyocytedisarray,coronarymicrovasculardisease,and
myocardialfibrosis.44,227,246Giventheriskofsuddendeath,considerableeffort
hasbeenmadeintryingtoidentifypatientswhomaybenefitfromprimary
prevention.Theconventionalriskfactorsforincreasedriskofsuddendeath
includethefollowing:(1)inadequatebloodpressureresponsetoexercise,(2)
familyhistoryofsuddendeathevents,includingappropriateICDtherapyfor
ventriculartachyarrhythmias,(3)unexplainedsyncope,(4)documented
nonsustainedventriculartachycardia(definedasthreeormorebeatsat≥120
beats/minonambulatoryECG),and(5)maximalleftventricularwallthickness
of30mmorgreater.6,7Usingthisstrategy,therehasbeenanappreciable
improvementovertimeinsuddendeathratesamongadultswithHCM.54Recent
datasuggestthatthepresenceofmultiplemutations,lategadolinium
enhancementonMRI,apicalaneurysm,andleftatrialsizemayalsoberisk
factorsforsuddendeathandcontributetothedecisionregardingICD
implantation.223,228,243–246,260,261Inspiteofimprovementsinriskstratification,
significantgapsinriskstratificationanddecisionmakingpersist.TheESCrisk
stratificationscorewasdevelopedtohelpguideshareddecisionmaking
regardingICDimplantationinadults223;however,thismaynotbeadequately
sensitivewhenassessingtheutilityofICDinprimaryprevention.262Thus,
althoughtheESCscoremayhelptoidentifypatientsathighestriskforsudden
deathevents,itdoesnotappeartobesensitiveenoughtoserveastheexclusive
guidetotherapyandmaymiss20%to30%ofeventswhena4%per5-yearrisk
cutoffvalueisused.Thisisconsistentwithdatasuggestingthatthenumberof
riskfactorsdoesnothelptoidentifychildrenoryoungadultsatriskfor
appropriateshockafteranICDisplacedforprimaryprevention.Therewasno
differenceinthecumulativerateoffirstinterventionwhenpatientswere
stratifiedbythenumberriskfactors,andalmost50%ofpatientswhoreceivedan
appropriateshockhadonlyasingleriskfactor.231
