Automated external defibrillators are easy to use and relatively affordable to purchase. Manufacturers have publicized these attributes in an effort to expedite the transition to PAD.42
While this publicity appears to have succeeded in broadening public awareness of cardiac arrest, it also may have contributed to imprudent AED deployment. Reports abound concerning purchase of defibrillators by relatively low-risk executives and concerned high school students.43,44
Before a strategy of PAD is further expanded, it is imperative to understand the costs and benefits associated with this potentially life-saving technology.
Ideally, the probability of cardiac arrest at each and every site would be known and AEDs could then be deployed accordingly. The results of the ongoing Public Access Defibrillation Trial will certainly help to answer a number of questions related to PAD.45
However, even after completion of this study, there will be many locations where AED deployment is considered, but the precise probability of cardiac arrest is unknown.
In the absence of comprehensive location-specific cardiac arrest rates, our analysis provides important guidance as to where AED deployment should be considered. The results of this study support the results of earlier studies suggesting that AED deployment in selected public locations is a cost-effective use of health resources.13,14,22
Our results also suggest that the current American Heart Association guidelines limiting AED deployment to sites with a 20% annual probability of cardiac arrest and cost per QALY gained of $30,000 may be overly conservative.
Several aspects of the sensitivity analysis warrant additional discussion. First, it is important to note that our analysis suggests that deployment of AEDs in locations with exceedingly low cardiac arrest rates is unlikely to be cost-effective even using the most optimistic assumptions. Second, the cost-effectiveness of AED deployment is sensitive to the probability that the deployed AED is actually used on a cardiac arrest that does occur at the site of deployment. Therefore, it is critical that deployed AEDs be accessible and easily identifiable to potential responders. Finally, it is important to note that the cost-effectiveness of AED deployment depends upon the relative benefit that AED deployment provides relative to EMS-D–based care. The cost-effectiveness of AEDs may be reduced by any improvement in cardiac arrest survival that might be generated by optimization of existing EMS-D systems. Therefore, many sites with low cardiac arrest rates might carefully consider encouraging optimization of existing EMS services rather than spending limited resources on AEDs that are unlikely to be used.
We were deliberately conservative in many of our estimates to avoid biasing our findings in favor of overly aggressive AED deployment. For example, we estimated annual mortality of 15% for cardiac arrest survivors, despite evidence that it may be significantly lower. We also took a conservative approach by estimating that only 25% of cardiac arrest victims survived their arrest despite evidence from Valenzuela et al. and Caffrey et al. that results may be significantly higher.8,10
Furthermore, we did not include potential utility gains that may be realized by the public from the sense of security (a.k.a. passive benefit) afforded by AED availability.46
Finally, we included substantial costs for AED maintenance and employee training despite evidence that training may not be necessary and AED maintenance costs may be minimal.10,47
There are several limitations to our study that are important to understand. First, it is important to acknowledge that the precise probability of cardiac arrests for any specific location is impossible to predict with certainty because each location serves a unique population. Our study relies on generalization of cardiac arrest rates in King County, Washington to other locations across the United States. While such generalization is not ideal, King County is a large metropolitan area with a diverse population that is representative of the overall population of the United States. Therefore, it is reasonable to generalize these cardiac arrest rates to other areas.48,49
Likewise, it is difficult to define with precision both the number of AEDs required for each location and the related probability that the device will be used. Becker et al. estimated the number of AEDs required at various public locations by using common sense (i.e., a shopping mall would require 1 AED per main entrance), and we applied these estimates to our model.16
While this approach may be criticized as arbitrary, the current decisions of precisely how many AEDs should be deployed in a shopping mall or airport are based on similar reasoning and likewise were applied to this analysis.10
Finally, while experience to date suggests that Good Samaritans consistently use publicly available AEDs on cardiac arrest victims, our analysis demonstrates that the cost-effectiveness of this intervention is reduced by any failure to use a publicly available AED on a nearby cardiac arrest victim; further experience will provide additional guidance as to how often this occurs.
Despite these limitations, this analysis provides important data to support a policy of AED deployment at selected public locations. Conversely, this analysis suggests that deployment of AEDs in other public locations including hotels and retail stores may not be justified on clinical and economic grounds alone. It is critical to understand that the cost-effectiveness of defibrillator deployment improves as the probability of that defibrillator being used on a cardiac arrest victim rises. Reaching a critical threshold of aggregate risk may occur within a single individual at high risk for cardiac arrest (justifying an implantable cardiac defibrillator) or among many moderate-risk individuals (thus warranting deployment of an AED). Using this framework correctly will help to ensure that AEDs are placed in the locations where the largest number of people stand to benefit. Further research is needed to more precisely determine which individuals and locations may benefit from AED availability.