title: Out-of-hospital cardiac arrest frequency and survival: evidence for temporal variability.
abstract: OBJECTIVE
  Some cardiac phenomena demonstrate temporal variability. We evaluated temporal variability in out-of-hospital cardiac arrest (OHCA) frequency and outcome.
  
  
  METHODS
  Prospective cohort study (the Resuscitation Outcomes Consortium) of all OHCA of presumed cardiac cause who were treated by emergency medical services within 9 US and Canadian sites between 12/1/2005 and 02/28/2007. In each site, Emergency Medical System records were collected and analyzed. Outcomes were individually verified by trained data abstractors.
  
  
  RESULTS
  There were 9667 included patients. Median age was 68 (IQR 24) years, 66.7% were male and 8.3% survived to hospital discharge. The frequency of cardiac arrest varied significantly across time blocks (p<0.001). Compared to the 0001-0600 hourly time block, the odds ratios and 95% CIs for the occurrence of OHCA were 2.02 (1.90, 2.15) in the 0601-1200 block, 2.01 (1.89, 2.15) in the 1201-1800 block, and 1.73 (1.62, 1.85) in the 1801-2400 block. The frequency of all OHCA varied significantly by day of week (p=0.03) and month of year (p<0.001) with the highest frequencies on Saturday and during December. Survival to hospital discharge was lowest when the OHCA occurred during the 0001-0600 time block (7.3%) and highest during the 1201-1800 time block (9.6%). Survival was highest for OHCAs occurring on Mondays (10.0%) and lowest for those on Wednesdays (6.8%) (p=0.02).
  
  
  CONCLUSIONS
  There is temporal variability in OHCA frequency and outcome. Underlying patient, EMS system and environmental factors need to be explored to offer further insight into these observed patterns.
authors: Rescu, Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital Division of Emergency Medicine, Department of Medicine, University of Toronto, Toronto, Ontario, Canada. brooksst@smh.toronto.on.ca
authors: Steven C
authors: SC
authors: Brooks
authors: Robert H
authors: RH
authors: Schmicker
authors: Thomas D
authors: TD
authors: Rea
authors: Tom P
authors: TP
authors: Aufderheide
authors: Daniel P
authors: DP
authors: Davis
authors: Laurie J
authors: LJ
authors: Morrison
authors: Ritu
authors: R
authors: Sahni
authors: Gena K
authors: GK
authors: Sears
authors: Denise E
authors: DE
authors: Griffiths
authors: George
authors: G
authors: Sopko
authors: Scott S
authors: SS
authors: Emerson
authors: Paul
authors: P
authors: Dorian
mesh_terms: D000368:Aged; D005260:Female; D006323:Heart Arrest / Q000453:epidemiology* / Q000401:mortality; D006801:Humans; D008297:Male; D011446:Prospective Studies; D015996:Survival Rate; D013997:Time Factors