title: Distinct hemodynamic profiles in patients with vasovagal syncope: a heterogeneous population.
abstract: OBJECTIVE
  The objective was to investigate mechanisms of vasovagal syncope by identifying laboratory techniques that characterize cardiovascular profiles in patients with vasovagal syncope.
  
  
  BACKGROUND
  The triggering mechanisms of vasovagal syncope are complex. The patient population is likely heterogeneous. We hypothesized that distinct hemodynamic profiles are definable with provocative maneuvers.
  
  
  METHODS
  Three groups of subjects were matched for age and gender: 16 patients with a history of syncope and an inducible vasovagal response during passive tilt table testing (70 degrees, 45 min, group I), 16 with a history of syncope, negative passive tilt table testing but positive isoproterenol tilt table testing (0.05 microg/kg per min, 70 degrees, 10 min, group II), and 16 control subjects. Beat-to-beat hemodynamic functions were determined noninvasively by photo-plethysmography and impedance cardiography.
  
  
  RESULTS
  At baseline, hemodynamic functions were not different among the three groups (supine). In response to tilt before any symptoms developed, total peripheral resistance decreased 9% +/- 14% in group I from baseline supine to tilt position but increased 27% +/- 18% in group II and 28% +/- 17% in controls (p < 0.001). Responses to isoproterenol were not significantly different between group II and controls in supine position. In response to tilt during isoproterenol infusion before any symptoms developed, total peripheral resistance decreased 24% +/- 20% in group II and increased 20% +/- 48% in controls (p = 0.002).
  
  
  CONCLUSIONS
  Group I patients may have impaired ability to increase vascular resistance during orthostatic stress. The inability to overcome isoproterenol-induced vasodilatation during tilt is important in triggering a vasovagal response in group II patients. These data suggest that the population with vasovagal response is heterogeneous. Distinct hemodynamic profiles in response to various provocative maneuvers are definable with noninvasive, continuous monitoring techniques.
authors.affiliation: Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
authors.forename: W K
authors.initials: WK
authors.lastname: Shen
authors.forename: P A
authors.initials: PA
authors.lastname: Low
authors.forename: R F
authors.initials: RF
authors.lastname: Rea
authors.forename: C M
authors.initials: CM
authors.lastname: Lohse
authors.forename: D O
authors.initials: DO
authors.lastname: Hodge
authors.forename: S C
authors.initials: SC
authors.lastname: Hammill
mesh_terms: D000328:Adult; D005260:Female; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007545:Isoproterenol; D008297:Male; D008875:Middle Aged; D013566:Sympathomimetics; D019462:Syncope, Vasovagal / Q000175:diagnosis* / Q000503:physiopathology; D018667:Tilt-Table Test; D014630:Vagus Nerve / Q000503:physiopathology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology
chemical_list: D013566:Sympathomimetics; D007545:Isoproterenol