Long QT SyndromeKCNQ1 Potassium ChannelEther-A-Go-Go Potassium ChannelsKCNQ Potassium ChannelsRomano-Ward SyndromeTorsades de PointesPotassium Channels, Voltage-GatedElectrocardiographyDeath, Sudden, CardiacSodium ChannelsMexiletineSyncopeJervell-Lange Nielsen SyndromeMutationAdrenergic beta-AntagonistsHexachlorophenePotassium ChannelsCation Transport ProteinsMutation, MissenseGenetic TestingPolymorphism, Single-Stranded ConformationalGenotypeHeart ArrestDNA Mutational AnalysisPhenotypeVentricular DysfunctionBradycardiaPedigreeAnti-Arrhythmia AgentsSympathectomyHeart Conduction SystemGenetic Predisposition to DiseaseAction PotentialsDeath, SuddenHeart RateHeterozygoteFamily HealthVentricular Premature ComplexesMyocytes, CardiacMuscle ProteinsExercise TestPatch-Clamp TechniquesDefibrillators, ImplantableElectrophysiologyTrans-ActivatorsFrameshift MutationHeartRisk FactorsPoint MutationIon Channel GatingInfant, NewbornTachycardia, VentricularMyocardiumPacemaker, ArtificialRisk AssessmentEpinephrineRegistriesElectrocardiography, AmbulatoryAmino Acid SubstitutionCHO CellsCardiac Pacing, ArtificialPotassiumPolymorphism, GeneticIon ChannelsCohort StudiesDNA-Binding ProteinsRetrospective StudiesGenetic VariationCricetinaePolymorphism, Single NucleotideCell LinePredictive Value of TestsGenetic LinkagePostureMembrane PotentialsExerciseProportional Hazards ModelsPrognosisDNAFollow-Up StudiesMolecular Sequence DataCase-Control StudiesSensitivity and SpecificityBase SequenceMyocardial ContractionAmino Acid SequenceTime FactorsIncidence