Each year, out-of-hospital cardiac arrests account for more than 400,000 deaths in North America. Although fewer than 10 percent of people survive after out-of-hospital cardiac arrests, using an automated external defibrillator (AED) has been shown to improve survival rates.
However, a recent retrospective, population-based cohort study in Canada showed that proximity to an AED might not always lead to using the device. More than 20 percent of out-of-hospital cardiac arrests occurred near a public AED that was inaccessible at the time of the arrest.
Lead researcher Christopher L.F. Sun, BASc, of the University of Toronto, and colleagues published their results online in the Journal of the American College of Cardiology on Aug. 15.
The researchers used data from the Toronto Regional RescuNET cardiac arrest database and identified all public location, nontraumatic out-of-hospital cardiac arrests in Toronto from January 2006 to August 2014. Public locations included public buildings, places of recreation, industrial facilities and outdoor public spaces. The researchers excluded hospitals and nursing homes.
They also obtained a list of registered AEDs from Toronto’s emergency medical service as of March 2015. In all, there were 912 publicly and privately owned AEDs at 737 addresses.
They considered an out-of-hospital cardiac arrest as being covered if it occurred within 100 meters of an AED regardless of the AED’s availability. They defined actual coverage as an out-of-hospital cardiac arrest that occurs within 100 meters of an AED and when the AED is available based on the location’s hours of operations. They then developed a spatiotemporal optimization model to determine AED locations to maximize coverage.
They calculated relative coverage loss as assumed 24/7 coverage minus actual coverage and then divided by assumed 24/7 coverage.
Of the 2,440 nontraumatic public out-of-hospital cardiac arrests, 451 were covered under assumed 24/7 coverage and 354 were covered under actual coverage. The relative coverage loss was 21.5 percent, while coverage loss during the evening, night and weekends was 31.6 percent.
The largest coverage losses occurred at schools (39.7 percent), industrial facilities (39.3 percent), recreation/sports facilities (37.1 percent) and offices (35.7 percent).
The study had a few potential limitations, according to the authors, including that AED registration is voluntary in Toronto, so the trial did not likely include all AEDs in the city. In addition, the definitions of coverage and survival were not the same. Further, they did not consider other potential barriers to bystander AED use, including legal liability, awareness, training, technological limitations and psychological factors.
“Public defibrillators (AEDs) must be both geographically and temporally accessible to assure optimal availability for individuals experiencing [out-of-hospital cardiac arrest],” the researchers wrote. “Incorporating both temporal and spatial data in determination of optimal AED placement could enhance accessibility for these individuals and improve outcomes. Legislation mandating AED registration with local EMS and 24/7 accessibility to the public would improve access.”