Spatiotemporal Stability of Public Cardiac Arrests

Background: Public access automated external defibrillator (AED) deployment and community cardiopulmonary resuscitation (CPR) programs should target geographical areas with high risk of out-of-hospital cardiac arrest (OHCA). Although these long-term, location-based interventions implicitly assume that the geographical OHCA risk remains stable over time, there is a paucity of evidence to support this assumption. Objective: To determine whether geographic OHCA risk is stable over time in a Canadian urban setting. Methods: We identified all atraumatic public-location OHCAs in Toronto, Canada from Jan. 2006 – Dec. 2014 and allocated each of them to one of the 140 neighborhoods defined by the City of Toronto. We then calculated the intra-class correlation (ICC) to measure the relative variability of OHCA counts within and between neighbourhoods over time. Results: We identified 2506 atraumatic public OHCAs. The figure shows that the average number of public OHCAs in Toronto was 278.4 (±41.4) per year. The highest-risk neighborhood had an average number of 12.9 OHCAs per year and remained the highest-risk neighborhood during six of the nine years. The four lowest-risk neighborhoods each had a rate of 0.1 OHCA per year. The ICC value was 0.67 [95% CI, 0.61 to 0.73], indicating that there was less year-to-year variation within the same neighborhood (i.e., more temporal stability) and more variation between neighborhoods. Conclusion: The OHCA rate in Toronto is stable at the neighborhood level over time. High-risk neighborhoods tend to remain high-risk, which supports focusing public health resources in those areas to increase the efficiency of these scarce resources and improve long-term impact