SyncopeSyncope, VasovagalBradycardiaMidodrineElectrocardiographyRecurrencePacemaker, ArtificialPostureElectrocardiography, AmbulatoryProspective StudiesFollow-Up StudiesCarotid SinusUnconsciousnessSymptom AssessmentTreatment OutcomeCardiac Pacing, ArtificialHeart BlockFludrocortisoneDepressionArrhythmias, CardiacDizzinessHeart RateDeath, Sudden, CardiacAutonomic DenervationDefibrillators, ImplantableLong QT SyndromeSeverity of Illness IndexQuestionnairesTachycardia, VentricularSick Sinus SyndromeRetrospective StudiesEtilefrineRisk FactorsReflex, AbnormalTime FactorsOrthostatic IntoleranceSupine PositionAutonomic Nervous SystemHeart ArrestAtrioventricular BlockTachycardiaHead-Down TiltElectrophysiologic Techniques, CardiacAdrenergic beta-AntagonistsBehavioral SymptomsPrevalence