title: The impact of catecholamines on defibrillation threshold in patients with implanted cardioverter defibrillators.
abstract: OBJECTIVE
  To determine the effect of physiologic catecholamine concentrations on the defibrillation threshold (DFT) in patients with implanted cardioverter defibrillators.
  
  
  BACKGROUND
  DFT is the minimum energy delivered by an implanted cardioverter defibrillator that successfully converts ventricular fibrillation. DFT testing is performed under conscious sedation. Since activities of daily living enhance sympathetic tone substantially over these nadir levels, it is important to explore the impact of catecholamines on DFT.
  
  
  METHODS
  In this double-blind study, we determined DFT by the step-down method. Patients (n = 50) were stratified by beta-blocker use and then randomized to a 7-minute infusion of epinephrine, norepinephrine, or placebo. After study infusion, DFT testing was repeated. Changes in DFT with different study medications were compared. Subgroup analyses of the effects of catecholamines on DFT, based on beta-blocker use, were also performed.
  
  
  RESULTS
  Norepinephrine reduced DFT from baseline measurements by 22.6% (P = 0.008). Neither epinephrine nor placebo impacted DFT (P = 0.999, P = 0.317, respectively). In the subgroup analyses, DFT was reduced with norepinephrine regardless of beta-blocker use, while epinephrine reduced DFT among those receiving beta-blockers. No change in DFT was observed in either of the placebo subgroups.
  
  
  CONCLUSIONS
  Elevation of plasma norepinephrine concentrations reduces the DFT, while elevations in epinephrine had no effect. Norepinephrine seems to reduce DFT regardless of beta-blocker therapy but epinephrine's effects are beta-blocker dependent.
authors.affiliation: College of Pharmacy, University of Connecticut, Storrs, Connecticut, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Kalus
authors.forename: C Michael
authors.initials: CM
authors.lastname: White
authors.forename: Michael F
authors.initials: MF
authors.lastname: Caron
authors.forename: Danette
authors.initials: D
authors.lastname: Guertin
authors.forename: Brian F
authors.initials: BF
authors.lastname: McBride
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Kluger
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage; D000368:Aged; D002395:Catecholamines / Q000008:administration & dosage; D017147:Defibrillators, Implantable; D004056:Differential Threshold / Q000187:drug effects*; D004311:Double-Blind Method; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods*; D004837:Epinephrine / Q000008:administration & dosage*; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000008:administration & dosage*; D017180:Tachycardia, Ventricular / Q000517:prevention & control*; D016896:Treatment Outcome
chemical_list: D000319:Adrenergic beta-Antagonists; D002395:Catecholamines; D009638:Norepinephrine; D004837:Epinephrine