The availability of an AED is a function of its geographic placement as well as its temporal availability, which is the time of day availability or accessibility. Many AEDs are placed in buildings that are not publicly accessible 24 hours a day, making those AEDs unavailable to bystanders.
Researchers Christopher Sun, BASc, and Timothy Chan, Ph.D., University of Toronto, analyzed cardiac arrests that occurred within 100 meters (328 feet) of a public AED in Toronto. They presented their findings at the American Heart Association’s Scientific Sessions 2015.
"The overall coverage loss was 21.5 percent," Chan said. "One in five cardiac arrests occurs when a nearby AED is not available."