title: Association between survival and early versus later rhythm analysis in out-of-hospital cardiac arrest: do agency-level factors influence outcomes?
abstract: OBJECTIVE
  Effectiveness of a resuscitation strategy may vary across communities. We hypothesize that a strategy that prioritizes initial emergency medical services (EMS) rhythm analysis (analyze early) will be associated with survival advantage among EMS systems with lower baseline (pretrial) ventricular fibrillation survival, whereas a strategy that prioritizes initial EMS cardiopulmonary resuscitation (analyze late) will be associated with survival advantage among systems with higher ventricular fibrillation baseline survival.
  
  
  METHODS
  We conducted a secondary, post hoc study of a randomized trial of out-of-hospital cardiac arrest. Subjects were stratified according to randomization status (analyze early versus analyze late) and EMS agency baseline ventricular fibrillation survival. We used a mixed-effects model to determine whether the association between favorable functional survival to hospital discharge and trial intervention (analyze late versus analyze early) differed according to EMS agency baseline ventricular fibrillation survival (<20% or >20%).
  
  
  RESULTS
  Characteristics were similar among patients randomized to analyze early (n=4,964) versus analyze late (n=4,426). For EMS agencies with baseline ventricular fibrillation survival less than 20%, analyze late compared with analyze early was associated with a lower likelihood of favorable functional survival (3.8% versus 5.5%; odds ratio [OR]=0.67 [95% CI 0.50, 0.90]). Conversely, among agencies with a ventricular fibrillation survival greater than 20%, analyze late compared with analyze early was associated with higher likelihood of favorable functional survival (7.5% versus 6.1%; OR=1.22 [95% CI 0.98, 1.52]). In the multivariable-adjusted model, for every 10% increase in baseline ventricular fibrillation survival, analyze late versus analyze early was associated with a 34% increase in odds of favorable functional survival (OR=1.34 [95% CI 1.07 to 1.66]).
  
  
  CONCLUSIONS
  The findings suggest that system-level characteristics may influence resuscitation outcomes.
authors: Department of Medicine, University of Washington, Seattle, WA. Electronic address: rea123@u.washington.edu.
authors: Thomas
authors: T
authors: Rea
authors: Department of Biostatistics, University of Washington, Seattle, WA.
authors: David
authors: D
authors: Prince
authors: University of Toronto and St Michael's Hospital, Toronto, Ontario, Canada.
authors: Laurie
authors: L
authors: Morrison
authors: Department of Emergency Medicine, University of Pittsburgh, Pittsburgh, PA.
authors: Clifton
authors: C
authors: Callaway
authors: Department of Emergency Medicine, Medical College of Wisconsin, Milwaukee, WI.
authors: Tom
authors: T
authors: Aufderheide
authors: Department of Emergency Medicine, Oregon Health and Science University, Portland, OR.
authors: Mohamed
authors: M
authors: Daya
authors: Department of Emergency Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors: Ian
authors: I
authors: Stiell
authors: Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Jim
authors: J
authors: Christenson
authors: Department of Biostatistics, University of Washington, Seattle, WA.
authors: Judy
authors: J
authors: Powell
authors: Department of Emergency Medicine, Oregon Health and Science University, Portland, OR.
authors: Craig
authors: C
authors: Warden
authors: Department of Biostatistics, University of Washington, Seattle, WA.
authors: Lois
authors: L
authors: van Ottingham
authors: Department of Medicine, University of Washington, Seattle, WA.
authors: Peter
authors: P
authors: Kudenchuk
authors: Department of Medicine, Johns Hopkins University, Baltimore, MD.
authors: Myron
authors: M
authors: Weisfeldt
mesh_terms: D002170:Canada / Q000453:epidemiology; D016887:Cardiopulmonary Resuscitation / Q000592:standards*; D004562:Electrocardiography; D004632:Emergency Medical Services / Q000592:standards*; D004636:Emergency Service, Hospital / Q000592:standards*; D006801:Humans; D058687:Out-of-Hospital Cardiac Arrest / Q000401:mortality / Q000503:physiopathology / Q000628:therapy; D010043:Outcome and Process Assessment, Health Care; D016032:Randomized Controlled Trials as Topic; D016019:Survival Analysis; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D014693:Ventricular Fibrillation / Q000401:mortality / Q000503:physiopathology / Q000628:therapy