SyncopeSyncope, VasovagalArrhythmias, CardiacDeath, Sudden, CardiacTachycardia, VentricularElectrocardiographyElectrocardiography, AmbulatoryDefibrillators, ImplantableVentricular FibrillationAnti-Arrhythmia AgentsBrugada SyndromeDeath, SuddenLong QT SyndromeElectrophysiologic Techniques, CardiacBradycardiaCircadian RhythmCardiac Pacing, ArtificialPacemaker, ArtificialHeart RateNAV1.5 Voltage-Gated Sodium ChannelTachycardiaMidodrineHeart Conduction SystemVentricular Premature ComplexesRecurrenceFollow-Up StudiesPredictive Value of TestsHeart ArrestTorsades de PointesPeriod Circadian ProteinsProspective StudiesPostureCardiac ElectrophysiologyBundle-Branch BlockFlecainideCardiac Complexes, PrematureSignal Processing, Computer-AssistedAdrenergic beta-AntagonistsElectric CountershockSuprachiasmatic NucleusRisk AssessmentStroke VolumeCarotid SinusRisk FactorsAutonomic Nervous SystemWolff-Parkinson-White SyndromeEncainideCardiomyopathy, DilatedUnconsciousnessHeart BlockFludrocortisoneBiological ClocksMyocardial InfarctionCryptochromesCardiomyopathy, HypertrophicArrhythmogenic Right Ventricular DysplasiaPrognosisKCNQ1 Potassium ChannelHeart VentriclesTime FactorsAutonomic DenervationAmiodaroneCircadian ClocksSick Sinus SyndromeRetrospective StudiesEtilefrineVentricular Dysfunction, LeftTreatment OutcomeQuinidineTachycardia, SupraventricularDizzinessMonitoring, PhysiologicIsoproterenolSensitivity and SpecificityOrthostatic IntoleranceCLOCK ProteinsAction PotentialsBlood PressureSupine PositionHeartAtrioventricular BlockReflex, AbnormalHead-Down TiltSyndromeHeart FailureAtrial FibrillationHypokalemia