title: Beta-blocker use and the changing epidemiology of out-of-hospital cardiac arrest rhythms.
abstract: BACKGROUND
  The incidence of ventricular fibrillation (VF) as the presenting rhythm in out-of-hospital cardiac arrest (OHCA) is declining, whereas pulseless electrical activity (PEA) is increasing. This changing epidemiology has occurred concomitant with an increase in beta-blocker use.
  
  
  OBJECTIVE
  The aim of this study was to measure the association of beta-blocker use among prehospital cardiac arrest patients with PEA versus VF as presenting rhythm.
  
  
  METHODS
  In this retrospective cohort study, records of all OHCA patients presenting to a single municipal hospital between 1 January 2001 and 31 December 2006 were reviewed. Age, sex, race, first documented rhythm, estimated down time, presence of bystander CPR, return of spontaneous circulation, beta-blocker use, and comorbid illnesses were noted. A Mantel-Haenzel chi-square was computed to describe the association between beta-blocker use and PEA, compared to beta-blocker use and VF. A sensitivity analysis was also performed to account for missing data, misclassification of beta-blocker use, misclassification of initial rhythm, confounding by unknown factors, and random error.
  
  
  RESULTS
  After exclusion of patients with asystole and patients in whom beta-blocker use was unclear/unknown, a cohort of 179 arrests was evaluated. The odds ratio for beta-blocker use among PEA versus VF patients was 3.7 (95% CI 1.9-7.2), and probabilistic adjustment for exposure and outcome misclassification, confounding, and random error increased the odds ratio to 5.0 (95% CI 1.1-31.0).
  
  
  CONCLUSIONS
  There appears to be an association between beta-blockers and the changing epidemiology of arrest rhythms, which may account for the increasing incidence of PEA and concomitant decrease in VF.
authors.affiliation: Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, CA 90590, United States.
authors.forename: Scott T
authors.initials: ST
authors.lastname: Youngquist
authors.forename: Amy H
authors.initials: AH
authors.lastname: Kaji
authors.forename: James T
authors.initials: JT
authors.lastname: Niemann
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use*; D000368:Aged; D015331:Cohort Studies; D004562:Electrocardiography; D004632:Emergency Medical Services; D005260:Female; D006323:Heart Arrest / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014693:Ventricular Fibrillation / Q000453:epidemiology
chemical_list: D000319:Adrenergic beta-Antagonists