Automated defibrillators

BMJ USA VOLUME 4 JANUARY/FEBRUARY 2004 (p7) E270 Three articles published in this issue (pp 23, 28, 45) nicely delineate several key issues related to use of automated external defibrillators (AEDs). These articles not only place the relative effectiveness of AEDs into better context, but they also provide insight into the limitations of AEDs and starting points for further research. AEDs have been highly effective in certain public settings where designated rescuers (eg, flight attendants or security guards) or a large number of bystanders are immediately available. AED use within first two minutes after collapse can dramatically improve outcome over traditional methods. In the most successful traditional emergency medical services (EMS) systems, overall rates of hospital admission following sudden out-of-hospital cardiac arrest associated with ventricular fibrillation (VF) exceeded 60% when bystanders witnessed the event and performed basic cardiopulmonary resuscitation (CPR). This is a near-miraculous statistic considering that VF is typically unexpected, unheralded, and almost uniformly lethal if CPR or defibrillation is not performed within the first few minutes. Nevertheless, even in such successful systems where the community knew and performed CPR in nearly 50% of cases, the majority of resuscitated patients still arrived at the hospital unconscious. In turn, only two thirds of these patients eventually awoke and survived with good neurological status. Moreover, when bystanders did not perform CPR, near-equal numbers of admissions occurred, but many fewer awoke and survived. AEDs have helped to improve those results. In a recent study of public use of AEDs at the Chicago airports, there was not only an extremely high resuscitation rate, but all of the resuscitated patients regained normal neurological status. In fact, the majority of survivors were awakening before EMS crews arrived, and almost all by hospital admission. This obviated the need for traditional intensive care unit (ICU) monitoring, mechanical ventilation, and other expensive therapies. Arguably, this increase in number of functional survivors might lead to additional health care costs (eg, placement of implantable defibrillators, cardiac surgery, coronary artery interventions), but this is a more desirable use of resources than avoidable and unfruitful ICU costs. However, despite well-deserved enthusiasm for AEDs, most cardiac arrests do not occur in public settings in view of multiple witnesses. The “successful” (high survival) reports about AEDs typically come from unique, targeted circumstances such as casinos, airplanes, and airports providing a high concentration of AEDs, intensive publicity, and many potential rescuers on site. As Liddle and colleagues state in this issue, AED use is optimal in the first 90 seconds. That time criterion generally limits success to circumstances predisposing to immediate recognition of a cardiac arrest by a bystander, along with immediate access to a highly visible AED. In the very first AED case reported from Chicago’s O’Hare International Airport, the collapse occurred in front of one of the authors (SCV), yet the time from collapse to shock still exceeded 90 seconds. Even under optimal circumstances such as this, it takes time to recognize the collapse, access the AED, expose the chest, apply the pads, perform final assessments, and start the device. Therefore, a “zero response interval” is not a zero interval to shock. All survivors in that study received shocks within five minutes and all received immediate performance of basic CPR techniques, even if briefly. By contrast, in their clinical trial of first-responder AED use, van Alem and colleagues reported “collapse to shock” intervals, demonstrating that even with firstresponders, shocks were not given for over 11 minutes. This information is critically pertinent because evolving evidence demonstrates that countershocks provided to a relatively ischemic heart may be detrimental. Controlled trials in systems with dispatch to scene arrival intervals of about 5 minutes (perhaps translating into a collapse to shock interval of 8 minutes or more) demonstrate that survival with good neurological recovery is improved if basic CPR is first provided for a few minutes prior to the first shock. Therefore, in addition to a potential type II statistical problem (not enough numbers to detect a difference in survival) and the discussed improvements in the dispatch process, it is quite possible that this study might have shown improved survival rates with alternative strategies for the timing of CPR and AED use. Also in this issue, Walker and colleagues raise further concern that widespread placement of AEDs in public locations (where only 10-15% of sudden deaths occur) may not be cost-effective. Again, these January/February 2004