title: Age-dependence of relative change in circulating epinephrine and norepinephrine concentrations during tilt-induced vasovagal syncope.
abstract: BACKGROUND
  Although vasovagal syncope (VVS) is preceded by a surge of circulating catecholamines (epinephrine [Epi] and norepinephrine [NE]) of adrenal/renal and synaptic origin, prevention of VVS with β-adrenergic blockade has been ineffective except in "older" VVS patients.
  
  
  OBJECTIVE
  We hypothesized that age-related differences of β-blocker effect may be due in part to differences in the relative magnitudes of Epi and NE release during an evolving faint, specifically, greater Epi/NE ratio in younger fainters compared to older patients. To assess this hypothesis, we measured changes in Epi/NE ratios in younger (<40 years) vs older (≥40 years) patients during head-up tilt-table test-induced VVS.
  
  
  METHODS
  The study comprised 29 patients (12 patients ≥40 years [mean 56 ± 10.7 years] and 17 patients <40 years mean 25 ± 5.7 years]) with recurrent suspected VVS in whom 70° head-up tilt testing reproduced symptoms. Arterial Epi and NE concentrations were measured at baseline (supine), 2 minutes of head-up tilt, and syncope.
  
  
  RESULTS
  Baseline Epi and NE concentrations and the Epi/NE ratio did not differ in younger and older groups (Epi: 90 ± 65 pg/mL vs 70 ± 32 pg/mL; NE: 226 ± 122 pg/mL vs 244 ± 183 pg/mL). However, Epi/NE ratio increased to a greater extent in younger fainters during head-up tilt and tended to be greater in younger patients at both 2 minutes (<40: 1.02 ± 1.29 vs ≥40: 0.40 ± 0.27, P = .11) and at symptoms (<40: 2.6 ± 1.26 vs ≥40: 1.6 ± 0.71, P = .03). At symptoms, Epi/NE ratio ≥2.5 was observed in 9 of 17 younger patients vs 1 of 12 older patients (P = .02).
  
  
  CONCLUSIONS
  Epi/NE ratios tend to be greater in younger fainters, a finding that may account in part for the observation that β-blocker therapy is less effective in reducing VVS susceptibility in younger individuals.
authors.affiliation: Cardiac Arrhythmia and Syncope Center, Department of Medicine (Cardiovascular Division), University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA. bendi001@umn.edu
authors.forename: David G
authors.initials: DG
authors.lastname: Benditt
authors.forename: Barry L S
authors.initials: BL
authors.lastname: Detloff
authors.forename: Wayne O
authors.initials: WO
authors.lastname: Adkisson
authors.forename: Fei
authors.initials: F
authors.lastname: Lu
authors.forename: Scott
authors.initials: S
authors.lastname: Sakaguchi
authors.forename: Stefanie
authors.initials: S
authors.lastname: Schussler
authors.forename: Erin
authors.initials: E
authors.lastname: Austin
authors.forename: Lin Yee
authors.initials: LY
authors.lastname: Chen
mesh_terms: D000328:Adult; D000367:Age Factors; D004837:Epinephrine / Q000097:blood*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood*; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D018667:Tilt-Table Test
chemical_list: D009638:Norepinephrine; D004837:Epinephrine