title: Temporal trends in sudden cardiac arrest: a 25-year emergency medical services perspective.
abstract: BACKGROUND
  Little is known about temporal trends in survival and prognostic characteristics of patients with out-of-hospital cardiac arrest treated by emergency medical services (EMS). We hypothesized that an evolving combination of beneficial and adverse factors may contribute to temporal patterns of survival.
  
  
  RESULTS
  We evaluated a population-based cohort of EMS-treated adult patients with cardiac arrest (n=12 591) from 1977 to 2001 in King County, Washington. Time was grouped into an initial 5-year period and 5 successive 4-year periods. We sought to determine the potential impact of temporal changes in prognostic factors typically beyond EMS control termed "fate" factors (for example, patient age) and factors implemented by EMS termed "program" factors (programs of dispatcher-assisted cardiopulmonary resuscitation and basic life support defibrillation). Several characteristics associated with survival changed over time. Observed survival did not change over time among all patients with cardiac arrest (OR=0.98 [0.95, 1.01], trend for each successive time period) and improved over time among patients with witnessed ventricular fibrillation (OR=1.05 [1.01, 1.09]). In models that included all patients with cardiac arrest and controlled for fate factors, advancing time period was associated with an increase in survival (OR=1.08 [1.05, 1.11]). Conversely, in models that controlled for program factors, advancing time period was associated with a decrease in survival (OR=0.95 [0.93, 0.98]). Results were similar among patients with witnessed ventricular fibrillation.
  
  
  CONCLUSIONS
  The static temporal pattern of survival from cardiac arrest appeared to result from an evolving balance of prognostic factors. Programs implemented by EMS appeared to counter adverse temporal trends in prognostic factors typically beyond EMS control.
authors.affiliation: Department of Medicine, University of Washington, Seattle, USA. rea123@u.washington.edu
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Rea
authors.forename: Mickey S
authors.initials: MS
authors.lastname: Eisenberg
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Becker
authors.forename: John A
authors.initials: JA
authors.lastname: Murray
authors.forename: Thomas
authors.initials: T
authors.lastname: Hearne
mesh_terms: D000208:Acute Disease; D000368:Aged; D016887:Cardiopulmonary Resuscitation / Q000706:statistics & numerical data / Q000639:trends; D015331:Cohort Studies; D004554:Electric Countershock; D004632:Emergency Medical Services / Q000706:statistics & numerical data* / Q000639:trends*; D005260:Female; D006323:Heart Arrest / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011379:Prognosis; D016019:Survival Analysis; D013997:Time Factors; D014861:Washington / Q000453:epidemiology