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thefirstheartsoundisaccentuated,andnonspecificsystolicmurmursmaybe
present.Ahighincidenceofmitralvalveprolapsehasbeenreportedinadults
withGravesdisease144,145buthasnotbeendemonstratedinchildren.146This
suggeststhattheappearanceoftheprolapseisrelatedtothedurationofthe
disease.
TheECGisatypical.Sinustachycardia,first-degreeatrioventricularblock,
andnonspecificST-segmentandT-wavechangesmaybepresent.Signsofatrial
andleftventricularenlargementaremorecommoninchildrenthaninadults.147
Althoughatrialfibrillationisquitecommoninadults,itisextremelyrarein
children.Radiographiccardiomegalyandaslightincreaseinpulmonaryvascular
markingsmaybeseen,especiallyinthesettingofCHF,althoughthisisrare
today.Theechocardiogramrevealshyperdynamicventricularcontractionswitha
variabledegreeofchamberenlargement.
Evaluationofcardiacfunctionbyradionuclideangiographyinthepresenceof
hyperthyroidismhasdemonstratedafallinleftventricularejectionfractionwith
exercise;however,uponrestorationofanormalthyroidstate,theejection
fractionshowsitsnormalexercise-inducedincrease.148Ingeneralthe
cardiovascularsysteminchildhoodtoleratestheeffectsofhyperthyroidismwell.
Inthepresenceofcardiacfailure,however,concomitantcardiovascularlesions
mustbeexcluded.Cardiovascularmanifestationsofhyperthyroidismare
reversiblewithtreatment;butifthediseaseisoflongstandingorpoorlytreated,
itmaypredisposetoirreversiblecardiacdysfunction.149

AddisonDisease
Adrenalinsufficiencymayoccuratanyageanddemonstratesnopredilectionfor
gender.Itusuallyresultsfromautoimmunedestructionoftheadrenalcortexand
ismanifestedbyweakness,hyperpigmentation,nausea,vomiting,lossofweight,
andhypotension.Whenacuteinonsetorwhenseeninpatientswhoare
metabolicallystressedbyaconcomitantillness,thediseasemaypresentwith
shockorcoma.
Cardiacinvolvementisduetothechronichypotensionandhypovolemia.

Chestradiographymaydemonstratediminishedcardiacsize.150TheECGmay
demonstratediffuselylowvoltages,sinusbradycardia,andfirst-degree
atrioventricularblock.Treatmentinvolvesreplacementofmineralocorticoid
hormonesandmustbecarriedoutwithcautionasCHFcanensue.This
complicationispresumablyduetotheacuteloadofsaltandwaterthatisthrust


uponthepreviouslyunloadedmyocardiumandisareadilytreatable,generally
transientcondition.151


DisordersofEnergyMetabolism
MitochondrialMyopathies
Themitochondrialmyopathiesaremuscleandsystemicdisorderscharacterized
bythepresenceofmitochondriawithabnormalstructure,number,and/or
function.Theyaretypicallycausedbydeletionsinmitochondrial
deoxyribonucleicacid(DNA),althoughsomearecausedbydefectsinnuclear
DNA.Thesedisordersinvolvecomplexesoftherespiratorychainandthusaffect
oxidativephosphorylation.
Chronicprogressiveophthalmoplegia,orKearns-Sayresyndrome,is
frequentlyencounteredamongthesediseases.Itisassociatedwithpigmentary
degenerationoftheretina,lackofcoordination,facialandlimbweaknesses,
shortstature,andendocrinologicanomalies.Thediseaseappearsinchildhood
andhasaprogressivecourse.Themostfrequentlyreportedcardiacanomalyis
progressiveheartblock.ECGsshouldbeperformedfrequentlyforearly
recognitionandappropriateimplantationofapacemaker.152Cardiomyopathy,
prolongedQTinterval,torsadesdepointes,atrialarrhythmias,andmitralvalvar
prolapsehavealsobeendescribed(seefurtheron).153–157
Myoclonicepilepsywithraggedredfibersandmitochondrialencephalopathy,
lacticacidosis,andstroke-likeepisodescanpresentwithadilated

cardiomyopathy.158PatientswithLeighsyndrome,orsubacutenecrotizing
encephalomyelopathy,candevelophypertrophiccardiomyopathyandconduction
systemdefects.159Mitochondrialdeoxyribonucleicacidismaternally
transmitted.Inheritance,therefore,followsnon-Mendelianpatterns.

BarthSyndrome
BarthsyndromeisanX-linkeddisorderduetoadefectintheTAZgene,
encodingtafazzin,aphospholipidtransacylaseinthemitochondrialmembrane.
Thisdefectleadstoadeficiencyofcardiolipin,causingdisruptionof
mitochondrialstructureandenergymetabolismaswellasadeficiencyin
adenosinetriphosphate.160Thediseaseischaracterizedbyadilated
cardiomyopathy,skeletalmyopathy,cyclicneutropenia,andgrowthretardation.
Thehearttypicallydisplayspoorcontractilityandisoftenhypertrabeculated,
showingfeaturesofventricularnoncompaction.Hypertrophyhasalsobeen