title: Causes for the declining proportion of ventricular fibrillation in out-of-hospital cardiac arrest.
abstract: OBJECTIVE
  The reported proportion of ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OHCA) has declined worldwide. VF decline may be caused by less VF at collapse and/or faster dissolution of VF into asystole. We aimed to determine the causes of VF decline by comparing VF proportions in relation to delay from emergency medical services (EMS) call to initial ECG (call-to-ECG delay), and VF dissolution rates between two study periods.
  
  
  METHODS
  Data from the AmsteRdam REsuscitation STudies (ARREST), an ongoing OHCA registry in the Netherlands, were used. We studied cardiac OHCA in the study periods 1995-1997 (n=917) and 2006-2012 (n=5695). Cases with available ECG and information on call-to-ECG delay were included. We tested whether initial VF proportion and VF dissolution rates differed between both study periods using logistic regression.
  
  
  RESULTS
  Despite a 15% VF decline between the periods, VF proportion around EMS call remained high in 2006-2012 (64%). The odds ratio (OR) for VF proportion in 2006-2012 vs. 1995-1997 was 0.52 (95%-CI 0.45-0.60, P<0.001), with similar rates of VF dissolution in both periods (P=0.83). VF decline was higher for unwitnessed collapse (OR 0.41, 95%-CI 0.28-0.58) and collapse at home (OR 0.50, 95%-CI 0.42-0.59), but not for categories of bystander CPR, age or sex.
  
  
  CONCLUSIONS
  VF proportion early after collapse remains high. VF decline is explained by the occurrence of less initial VF, rather than faster dissolving VF. An increase in unwitnessed OHCA and collapse at home contributes to the observed VF decline.
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Electronic address: m.hulleman@amc.nl.
authors.forename: Michiel
authors.initials: M
authors.lastname: Hulleman
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Jolande A
authors.initials: JA
authors.lastname: Zijlstra
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Stefanie G
authors.initials: SG
authors.lastname: Beesems
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Marieke T
authors.initials: MT
authors.lastname: Blom
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: van Hoeijen
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Reinier A
authors.initials: RA
authors.lastname: Waalewijn
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Hanno L
authors.initials: HL
authors.lastname: Tan
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Jan G P
authors.initials: JG
authors.lastname: Tijssen
authors.affiliation: Department of Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Rudolph W
authors.initials: RW
authors.lastname: Koster
mesh_terms: D000368:Aged; D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D004632:Emergency Medical Services; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D016017:Odds Ratio; D058687:Out-of-Hospital Cardiac Arrest / Q000453:epidemiology / Q000209:etiology* / Q000628:therapy; D012042:Registries; D012189:Retrospective Studies; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000150:complications / Q000453:epidemiology*
keywords: Cardiopulmonary resuscitation; Heart arrest; Tachyarrhythmias; Ventricular fibrillation