title: Cardiac arrest witnessed by prehospital personnel: intersystem variation in initial rhythm as a basis for a proposed extension of the Utstein recommendations.
abstract: OBJECTIVE
  To test the hypothesis that intersystem variation in initial rhythm among EMS-witnessed arrests is of sufficient magnitude to warrant standardization of survival by creation of an Utstein-style denominator of EMS-witnessed ventricular fibrillation (VF).
  
  
  METHODS
  We conducted a planned subset analysis of a prospective observational cohort study of consecutive EMS-witnessed adult cardiac arrests occurring in New York City and meeting Utstein entry criteria. The primary outcome measure was intersystem variation in frequency of EMS-witnessed VF in New York City compared with that in other EMS systems. Secondary outcome measures were variations in survival after EMS-witnessed VF arrests and overall survival after all EMS-witnessed arrests.
  
  
  RESULTS
  Intersystem variation showed a threefold difference in the frequency of EMS-witnessed VF (24% in New York City versus 77% in Scotland; 99% confidence interval [CI] for 53% difference, 43% to 63%; P < 10(-7), a twofold difference in survival after EMS-witnessed VF (25% in NYC versus 48% in King County, WA; 99% CI for 23% difference, 6% to 39%; P < .002), and a fourfold difference in survival after all EMS-witnessed arrests (9% in New York City versus 35% in King County; 99% CI for 26% difference, 18% to 34%; P < 10(-7).
  
  
  CONCLUSIONS
  The marked variation in frequency of initial rhythm in EMS-witnessed arrests suggests that a modified Utstein denominator of EMS-witnessed VF would facilitate more uniform intersystem comparison of survival in this unique cohort. However, even after adjustment for initial rhythm, large residual intersystem survival differences remain unexplained.
authors.affiliation: Department of Emergency Medicine, Albert Einstein College of Medicine, Bronx, NY., USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Gallagher
authors.forename: G
authors.initials: G
authors.lastname: Lombardi
authors.forename: P
authors.initials: P
authors.lastname: Gennis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D003625:Data Collection / Q000592:standards*; D004632:Emergency Medical Services; D004634:Emergency Medical Technicians; D005260:Female; D006323:Heart Arrest / Q000401:mortality*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008499:Medical Records / Q000592:standards*; D008875:Middle Aged; D009519:New York City / Q000453:epidemiology; D015588:Observer Variation; D016019:Survival Analysis; D014693:Ventricular Fibrillation / Q000401:mortality*