On-site, public-access, automated external defibrillators (AEDs) more than double the chance of neurologically intact survival after an out-of-hospital cardiac arrest, compared with patients who do not receive AED treatment. This finding comes from a real-world, population-based study in the North Holland province of the Netherlands, which has been published in Circulation.

The research follows on from a controlled clinical trial between 2000 and 2002 by the Amsterdam Resuscitation Study (ARREST) group, in which the random allocation of AEDs to first responders (for example, firefighters and policemen) was investigated. Since then, public-access AEDs have been placed in Amsterdam airport and various other public locations; however, AED placement is uncontrolled and training of lay responders is by local initiative. During the study period, the North Holland province had a population of 2.4 million inhabitants, 67 AEDs available for dispatch with first responders, and 1,583 on-site AEDs (generally accompanied by trained lay rescuers). Dr. Jocelyn Berdowski from the Academic Medical Center at the University of Amsterdam “was curious to see how well responders did without the structure of a research program, [and] to measure the effectiveness of both dispatched and on-site AEDs by quantifying how long it takes from the emergency call before a patient receives a shock.”

The researchers recorded all consecutive patients with an out-of-hospital cardiac arrest of presumed cardiac origin on whom resuscitation had been attempted by emergency medical personnel between 1 January 2006 and 31 March 2009. A total of 2,833 patients were included; an on-site AED was used to treat 128 patients, an AED was dispatched to 478 patients, and 2,227 patients received no AED treatment. The primary outcome was neurologically intact survival.

The use of an on-site AED reduced the time to first shock from 11 to 4.1 min, and was associated with a significantly higher rate of neurologically intact survival than patients without AED treatment (50% vs 14%, unadjusted OR 5.63, 95% CI 3.91–8.10). Even after adjustment for confounding factors (such as age, public location, witness status, bystander cardiopulmonary resuscitation, dispatched AED area, and initial rhythm) the OR remained significant (adjusted OR 2.72, 95% CI 1.77–4.18). Among patients with a shockable initial rhythm, those treated with an on-site AED had a significantly higher rate of neurologically intact survival than those without AED treatment (64% vs 28%, unadjusted OR 4.26, 95% CI, 2.77–6.57). According to Dr. Berdowski, “the survival rate is similar to that previously reported in a study setting (the Public Access Defibrillation Community Trial).”

By contrast, dispatching an AED with a first responder reduced the time from call to first shock by only 2.5 min. Neurologically intact survival was only 17.2%, and not significantly different from no AED treatment (unadjusted OR 1.07, 95% CI 0.82–1.39; adjusted OR 1.19, 95% CI 0.89–1.60). This marginal survival benefit is probably a consequence of the limited reduction in time to shock, at the end of the survival window.

The investigators estimate that 1.2 and 3.6 lives per 1 million inhabitants were saved every year by dispatched and on-site AEDs, respectively. However, “although on-site AEDs [are] very effective, they are mostly used in public locations, while the majority of [cardiac] arrests occur at home,” cautions Dr. Berdowski. “The fact that only 5% of all out-of-hospital cardiac arrests are treated with an on-site AED puts the effectiveness at a population level in perspective.”

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Nonetheless, Professor Joseph Ornato from the Department of Emergency Medicine at Virginia Commonwealth University, USA believes that the findings from this study “further extend our knowledge regarding the effectiveness of AED deployment [and] delivery strategies in the community ... because the Amsterdam experience is from registry tracking of 'real-world' AED deployment rather than a controlled clinical trial with trained lay rescuers.”

The number of public-access AEDs could be increased to improve their availability, but Dr. Berdowski believes that “we need to find a way to further shorten the time to defibrillation without the limitation of current on-site AEDs, [which are] only effective for a small population in a public location. The ARREST group is investigating a method to combine the use of on-site AEDs with the method of dispatching: if a dispatcher suspects a cardiac arrest, they can warn lay rescuers in the vicinity of the patient by a text message that includes the location of the patient and the nearest AED.”