Author + information
- Robert J. Myerburg, MD∗ ()
- ↵∗Reprint requests and correspondence:
Dr. Robert J. Myerburg, Division of Cardiology (D-39), University of Miami Miller School of Medicine, P.O. Box 016960, Miami, Florida 33101.
Despite intense system development efforts and community resources that have gone into programs for responding to out-of-hospital cardiac arrest (OHCA), outcomes remain disappointing. Available statistics suggest that cumulative national survival rates are no better than 10% of the >350,000 OHCAs that occur in the United States annually (1). Among those who do survive, a subset remains burdened by consequent neurological dysfunction. The recognition that there are exceptions with better outcomes among some response systems compared with most suggests that there is hope for improving these disturbing outcomes in the future (2).
Viewed globally, the organizational and operational elements of community response systems are burdened by limitations, with a recent analysis by the Institute of Medicine (IOM) suggesting that almost every component needs attention to achieve meaningful improvement in outcomes (3). These include: prompt recognition and better responses to the onset of cardiac arrest by lay witnesses; the role of emergency medical services (EMS) contact centers, bystander interventions, and automated external defibrillator (AED) deployment; prompt dispatch and timely arrival of EMS systems at the patient’s side; improvement of pre-hospital and in-hospital transitions of care; and development of strategies for transporting at least some categories of post-cardiac arrest victims to centers of excellence for advanced post-arrest care (Figure 1). Among the proposed strategies to remedy the limitations are involvement by community leadership in optimizing organization and resources, public education that highlights the benefits and encourages the willingness of action by lay responders, and a national cardiac arrest registry serving as a resource for data evaluation and self-improvement strategies on a local level. The latter is based on the concept that national statistics are no more or less than the sum of the local statistics, and the extent to which communities can draw on each other’s strategies, programs, and outcomes will ultimately determine how well we perform as a nation. These ambitious proposals will take time to devise and implement but that should not discourage concurrent research efforts that may contribute interim improvements in outcomes.
One encouraging element of recent research has been the generation of data supporting the intuitive notion that bystander cardiopulmonary resuscitation (CPR) and AED deployment can improve outcomes (4,5). The parallel observation that bystander CPR and AEDs are used less frequently than desired seems to be due to a combination of inadequate public education, limited community planning and incentives, and perhaps the sense of uncertainty and insecurity of potential responders. In contrast, there have been initiatives in some communities to optimize AED deployment and accessibility at the time of a cardiac arrest. These planning systems have included voluntary strategic placement of AEDs in communities, the application of communication systems that would bring responder and AED together at the site of a cardiac arrest in a timely fashion (Figure 1), and the availability of voluntary AED registries for identifying sites with higher probabilities of accumulating more cardiac arrests. Such systems provide sources of data that would allow planners to redeploy AEDs to sites most likely to benefit from rapid access, after accumulating a sufficient database of OHCA incidence at specific sites. At the same time, systems integrating EMS communications centers, bystanders, AEDs, and victims are suggested to concurrently improve responses times and outcomes (6). An example is a study from Denmark that assessed the value of a citywide grid and integration of a parallel EMS communications system to direct first responders to the nearest available AED at the time of an emergency (7). One observation in that study was that, initially, AEDs were not optimally deployed in public locations. However, as data were analyzed according to event distribution, strategic deployment improved as more AEDs were placed in the community over time.
In this issue of the Journal, Sun et al. (8) provide data on an intuitive limitation of response systems, namely the accessibility of an AED when needed, based not just on its physical location but also considering its actual availability at different times of the day and night. This retrospective population-based cohort study, which used information in the well-developed Toronto Regional RescuNET database, identified that among 2,440 OHCAs occurring between January 2006 and August 2014, a total of 451 (18.5%) were covered by registered AEDs. AED coverage was defined as an OHCA occurring within 100 meters of a registered AED. However, among these events, only 354 had actual coverage, defined by both AED location and accessibility at the time of the OHCA. Thus, there was a 21.5% reduction in actual coverage, compared with the apparent coverage based on location alone. One other study had previously demonstrated the same principle (9), but Sun et al. (8) went on to develop an optimization model integrating time and distance to improve AED availability based on actual access. With this theoretical model, they predicted a 25.3% improvement in actual coverage.
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. Whether the 25% improvement in accessibility (8) 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.
As intriguing as this observation is, and with its practical implications obvious, there are limitations to the impact that improvements in actual access would have on overall OHCA survival. It has been well documented, both from the Toronto experience as well as many other communities around the world, that public location cardiac arrest constitutes a minority of the overall public health burden of OHCA. Approximately 70% to 80% of all OHCAs occur in the home, not public locations, and survival after in-home cardiac arrest is far lower than observed in public locations (10). This unfortunate outcome is likely due, at least in part, to a response time–dependent higher probability of nonshockable rhythms at first contact in-home. Thus, the impact of the study by Sun et al. (8) is relatively small when viewed in the context of the overall OHCA burden; it would be of interest to explore whether some modification of AED access strategies could be applied to in-home OHCAs as well. The few condominium buildings included in this study, which did not have AED accessibility limitations, are not representative of the much more dominant single-family dwellings. A previous study of home AED deployment for assumed relatively high-risk patients did not demonstrate a statistically significant benefit (11), but I have long been intrigued by a suggestion of neighborhood-based AED deployment with locally designated responders (12). This proposal has not materialized, but perhaps the concept should be revisited in the future, keeping in mind the principle of accessibility.
The limitations cited are not intended to minimize the potential contribution of the investigators’ observations in this report (8) but rather question whether parallel strategies could be expanded to the larger problem of in-home OHCA. Until we have strategies tailored to the larger segment of the OHCA burden, the magnitude of incremental benefit will be limited.
A second, more general issue relates to the broader perspective of cardiac arrest as a public health burden. Much of the emphasis in this report (8), as well as in the IOM report on the status of cardiac arrest in the United States (3), focused on the response to an impending or actual cardiac arrest. A much larger epidemiological problem is the prediction and prevention of cardiac arrest, which is an aspect of OHCA that is complementary to improvements in response strategies. A larger cumulative benefit to society would be achieved by both reducing the number of OHCAs and achieving better outcomes from those that do occur (Figure 1). 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. (8) We now need a parallel effort to develop a roadmap for improving prediction and prevention of OHCA.
↵∗ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
Dr. Myerburg is supported in part by the AHA Chair in Cardiovascular Research at the University of Miami Miller School of Medicine and by a research grant from the Miami Heart Research Foundation.
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