title: The impact of carvedilol on the defibrillation threshold.
abstract: BACKGROUND
  Defibrillation threshold (DFT) is the minimum energy required to successfully terminate ventricular fibrillation. Epinephrine has been shown to increase the DFT in the beta-blocker naïve, but using cardioselective beta-blockers leads to a reduction in the DFT on infusion of epinephrine and norepinephrine. We sought to determine the impact of carvedilol therapy on the DFT after infusion of epinephrine and norepinephrine.
  
  
  METHODS
  DFT was determined in patients receiving carvedilol by the step-down method (baseline DFT), and then patients (n = 27, 67.3 years, 70.0% were male, average left ventricular ejection fraction = 19%) were randomized to a 7-minute infusion of norepinephrine, epinephrine, or placebo in a double-blind manner. After the study drug infusion, DFT testing was repeated (experimental DFT) and results were compared between groups.
  
  
  RESULTS
  No differences in intragroup DFTs were observed among carvedilol-treated patients receiving norepinephrine (9.4 +/- 4.6 J vs 11.1 +/- 7.8 J; P = .589), epinephrine (10.6 +/- 5.3 J vs 9.8 +/- 6.3 J; P = .779), or placebo (11.1 +/- 7.0 vs 8.5 +/- 4.2; P = .349).
  
  
  CONCLUSIONS
  Carvedilol prevents alterations in DFT produced by stress levels of catecholamines.
authors.affiliation: Division of Clinical Pharmacology and John A. Oates Institute for Experimental Therapeutics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Brian F
authors.initials: BF
authors.lastname: McBride
authors.forename: C Michael
authors.initials: CM
authors.lastname: White
authors.forename: James S
authors.initials: JS
authors.lastname: Kalus
authors.forename: Danette C
authors.initials: DC
authors.lastname: Guertin
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Clyne
authors.forename: William L
authors.initials: WL
authors.lastname: Baker
authors.forename: Jeffery
authors.initials: J
authors.lastname: Kluger
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000368:Aged; D002227:Carbazoles / Q000494:pharmacology*; D000077261:Carvedilol; D017147:Defibrillators, Implantable; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000494:pharmacology*; D011412:Propanolamines / Q000494:pharmacology*; D013318:Stroke Volume; D014693:Ventricular Fibrillation
chemical_list: D000319:Adrenergic beta-Antagonists; D002227:Carbazoles; D011412:Propanolamines; D000077261:Carvedilol; D009638:Norepinephrine; D004837:Epinephrine