SyncopeSyncope, VasovagalBradycardiaMidodrineElectrocardiographyPacemaker, ArtificialElectrocardiography, AmbulatoryPostureRecurrenceCarotid SinusUnconsciousnessHeart BlockCardiac Pacing, ArtificialFludrocortisoneArrhythmias, CardiacAutonomic DenervationLong QT SyndromeDeath, Sudden, CardiacDefibrillators, ImplantableHeart RateTachycardia, VentricularSick Sinus SyndromeEtilefrineDizzinessOrthostatic IntoleranceSupine PositionHeart ArrestAtrioventricular BlockReflex, AbnormalHead-Down TiltElectrophysiologic Techniques, CardiacAutonomic Nervous SystemTachycardia