Fewer than 10 percent of people survive out-of-hospital cardiac arrests. Their chance to live increases, though, if they are treated with an automated external defibrillator (AED) and if bystanders perform cardiopulmonary resuscitation (CPR) on them. Thus, more communities have started to place AEDs in public locations.

Still, a recent Canadian study showed that those initiatives might not be enough to provide people with a better chance to survive cardiac arrests. Results were published online in the Journal of the American College of Cardiology.

The researchers analyzed a database to identify out-of-hospital cardiac arrests occurring between January 2006 and August 2014 in Toronto. Of the cardiac arrests that occurred within 100 meters of a registered AED, 21.5 percent were inaccessible at the time of the episode.

The coverage loss was 31.6 percent during the evening and weekends, which was when 61 percent of out-of-hospital cardiac arrests occurred. The largest coverage losses were at schools (39.7), industrial facilities (39.3 percent), recreation/sports facilities (37.1 percent) and offices (35.7 percent), which accounted for a combined 63.9 percent of AED locations.

Based on a spatiotemporal model they developed, the researchers said they could improve coverage by 25.3 percent, which in turn could possibly help increase survival. They recommended that countries pass legislation mandating that AEDs operate 24/7 and register with local emergency medical service personnel in order to improve access to AEDs.

“The observation of nonaccessibility—based on time of day and weekday versus weekend—and translating that limitation to actual coverage, is intriguing and important, and should be woven into planning strategies for AED locations both by reanalyzing existing deployment and for future program planning,” Robert J. Myerburg, MD, of the University of Miami Miller School of Medicine, wrote in an accompanying editorial. “Whether the 25 percent improvement in accessibility is realistic can only be demonstrated by prospective studies of deployment strategies based on this model and variations of the model developed by these investigators.”

Even if AEDs were more accessible in public locations, Myerburg noted that approximately 70 to 80 percent of out-of-hospital cardiac arrests occur in the home, where survival rates are much lower. Although this study and a report from the Institute of Medicine (IOM) have examined responses to cardiac arrests, Myerburg mentioned that predicting and preventing cardiac arrests are even more important and pressing issues.

“The IOM report on cardiac arrest provides a roadmap for improving responses to cardiac arrest, an example of which is evident in the study by Sun et al,” he wrote. “We now need a parallel effort to develop a roadmap for improving prediction and prevention of [out-of-hospital cardiac arrest].”