BACKGROUND: Although increased dissemination of automated external defibrillators (AEDs) has been associated with more frequent AED use, the trade-off between the number of deployed AEDs and coverage of cardiac arrests remains unclear. We investigated how volunteer-based AED dissemination affected public cardiac arrest coverage in high- and low-risk areas.

METHODS AND RESULTS: All public cardiac arrests (1994-2011) and all registered AEDs (2007-2011) in Copenhagen, Denmark, were identified and geocoded. AED coverage of cardiac arrests was defined as historical arrests ≤100 m from an AED. High-risk areas were defined as those with ≥1 arrest every 2 years and accounted for 1.0% of the total city area. Of 1864 cardiac arrests, 18.0% (n=335) occurred in high-risk areas throughout the study period. From 2007 to 2011, the number of AEDs and the corresponding coverage of cardiac arrests increased from 36 to 552 and from 2.7% to 32.6%, respectively. The corresponding increase for high-risk areas was from 1 to 30 AEDs and coverage from 5.7% to 51.3%, respectively. Since the establishment of the AED network (2007-2011), few arrests (n=55) have occurred ≤100 m from an AED with only 14.5% (n=8) being defibrillated before the arrival of emergency medical services.

CONCLUSIONS: Despite the lack of a coordinated public access defibrillation program, the number of AEDs increased 15-fold with a corresponding increase in cardiac arrest coverage from 2.7% to 32.6% over a 5-year period. The highest increase in coverage was observed in high-risk areas (from 5.7% to 51.3%). AED networks can be used as useful tools to optimize AED placement in community settings.