American Heart Association Report on the Second Public Access Defibrillation Conference, April 17–19, 1997
During the past 20 years, morbidity and mortality rates for nearly all types of cardiovascular disease have declined. However, there has been little decline in incidence or improvement in outcome after sudden cardiac arrest. Each day ≈1000 Americans experience sudden cardiac arrest.1 2 Of these, ≈70% experience ventricular fibrillation. Although patients with advanced cardiac conditions have at least a 50% incidence of sudden death,3 individuals with severe heart disease collectively constitute only a very small percentage of sudden deaths in this country.1 Therefore, although prevention is clearly the best approach to the problem of sudden cardiac arrest, such preventive treatments may be difficult and costly to implement.
External CPR and defibrillation were first described as effective treatments for sudden cardiac arrest >30 years ago. However, survival after out-of-hospital cardiac arrest is still poor. The American Heart Association previously addressed this problem by emphasizing the importance of the chain of survival4 : early access, early CPR, early defibrillation, and early advanced life support. Because early defibrillation is the single most important intervention, the American Heart Association challenged manufacturers to develop simple, low-cost automatic defibrillators for use by targeted groups at locations in which large numbers of people congregate.5
We previously proposed extension of this enhanced defibrillation strategy to include defibrillation by minimally trained members of the public, referred to as PAD.6 This strategy seeks to concentrate distribution of AEDs at specific sites at which sudden cardiac arrest occurs frequently (eg, public places in which large numbers of older people are present, such as airports and casinos). In addition, training of personnel to provide early defibrillation when sudden cardiac arrest occurs in airlines, trains, or buses offers an additional opportunity to improve survival after sudden cardiac arrest.
In 1994, a group of representatives from the scientific, industrial, medical, nursing, public health, engineering, and regulatory communities met to discuss this new strategy to treat sudden cardiac arrest.7 Since then, considerable advances have occurred: defibrillators are smaller and easier to use, and early defibrillation programs are being implemented in casinos, work sites, and airlines in the United States. Therefore, a second conference was convened April 17–19, 1997, in Washington, DC. This conference attracted more than 500 participants, with extensive representation from the scientific, industrial, clinical, and regulatory communities. The remainder of this report outlines the content of the sessions, the interactive workshops that constituted the formal program, and the recommendations of conference participants.
Levels of PAD
The four levels of defibrillation are as follows.
Level 1: Traditional First-Responder Defibrillation
This level includes defibrillation efforts by police, highway patrol personnel, and firefighter personnel. In many locations, firefighters are the first responders to cardiac emergencies, and yet they are often prohibited by regulations and states codes from providing early defibrillation.
Level 2: Nontraditional First-Responder Defibrillation
This level includes defibrillation efforts by lifeguards, security personnel, and airline flight attendants.
Level 3: Citizen CPR Defibrillation
This level refers to citizens and laypeople who have received AED training. These individuals are interested in providing emergency cardiac care, usually in the setting of a home in which a family member who is a high-risk patient resides.
Level 4: Minimally Trained Witness Defibrillation
This level refers to individuals who happen to witness a cardiopulmonary emergency and have an AED available (for example, through a worksite defibrillation program). In general, this level occurs most commonly in the home or at a worksite where one group of people has been trained and other groups have not. The untrained witness wants to help out and assist, but she has not yet received formal AED training. Another example of this level is possible if AEDs become accessible in the so-called “fire-extinguisher mode,” in which the AED location is displayed prominently and any witness to an emergency has access to these devices. At present, both Food and Drug Administration and state regulations permit physician prescription of AEDs to individual homes. This level will become more feasible with the introduction of newer technology that provides more voice prompts to the user, automatic 911 dialing, and possibly 911 dispatcher–assisted defibrillation.
A potential for misunderstanding exists when discussions about PAD are interpreted as efforts advocating AED use at a different level. It is critical to convey a clear understanding of which level of PAD is under discussion.
Current State of EMS
The existing EMS systems in some cities are highly effective at treating sudden cardiac arrest. For example, the EMS systems of Seattle and King County, Washington, have reported survival to discharge of 13.9% and 17.2%, respectively, among all cases of sudden cardiac arrest.8 9 However, many other cities are unable to achieve such results. For example, an EMS system of firefighters providing CPR and defibrillation followed by paramedics providing advanced life support had a survival–to–hospital discharge rate of 1.4% in New York City10 ; an EMS system of paramedics providing advanced life support had a survival–to–hospital discharge rate of 1.8% in Chicago.11 In such cities, the presence of urban congestion and large residential or office buildings result in a prolonged time interval between the onset of cardiac arrest and the provision of defibrillation because horizontal and vertical times to the treatment of victims of sudden cardiac arrest are prolonged. Provision of early defibrillation by a strategy such as PAD may dramatically improve outcomes after sudden cardiac arrest in these communities.
In summary, the consensus expressed at this conference was that local data must drive local solutions. In cities in which the current approach to sudden cardiac arrest results in good survival, PAD may have limited impact. However, existing approaches to sudden cardiac arrest result in poor survival rates (ie, <5% survival to hospital discharge) in most settings. PAD may be of critical importance in these communities.
The technology available to treat sudden cardiac arrest is evolving rapidly because of changes in knowledge and device design. Knowledge about the optimal waveform type and shock strength that should be used in AEDs is increasing. There are two types of waveforms, monophasic and biphasic (Figure⇓). With monophasic waveforms, the current travels in only one direction. With biphasic waveforms, the current passes from one pad to the other, then reverses. At present, the majority of approved AEDs use a monophasic truncated or monophasic damped sine exponential waveform. Recent work suggests that the truncated biphasic exponential waveform may be superior for external defibrillation. For example, animal and human studies of internal defibrillation have reported that the defibrillation thresholds and the median shock strength required to defibrillate are significantly lower for some biphasic waveforms than for monophasic waveforms.12 Cardiac electrophysiological studies of external (transthoracic) truncated exponential and the underdamped sine biphasic waveforms in patients receiving an implantable cardioverter-defibrillator demonstrated that both of these biphasic waveforms were equally successful or more successful at defibrillating than external critically damped sine wave shocks of the same or higher energy.13 14 These preliminary findings should be confirmed by additional studies, because not all truncated biphasic external waveforms are equally efficacious for defibrillation.15
Some experts believe that biphasic waveforms are not superior to other waveforms in defibrillation. This view is based primarily on two facts. First, all or almost all waveforms in currently available external defibrillators can defibrillate if the shock strength is sufficiently high. Second, as yet, no studies in humans have demonstrated that survival after sudden cardiac arrest is greater with a biphasic truncated exponential waveform than with other waveforms.
There is no consensus on the optimum shock strength for the output of a biphasic truncated exponential external defibrillator. In one study, the defibrillation efficacy of a 130-J truncated exponential biphasic waveform was equivalent to that of a 200-J critically damped sine waveform.13 However, the statistical power was insufficient to determine whether the defibrillation efficacy of a 130-J biphasic truncated exponential waveform was less than that of a 360-J critically damped sine waveform. Although prehospital studies of defibrillation with the biphasic truncated exponential waveform are under way, the results of these studies are not available at present. In summary, until more information is available, clinical trials of PAD should include multiple waveforms and multiple devices.
Several manufacturers have responded to the American Heart Association’s challenge to develop a small, lightweight, simple defibrillator for use by the public (Table⇓). The number and type of available devices are rapidly evolving. In future, the price, weight, and complexity of these devices will most likely continue to decrease.
Several American and international investigators have demonstrated promising results from uncontrolled field studies of expanded use of defibrillation. For example, in a midsize American community, 58% of patients with ventricular fibrillation who were defibrillated early by police survived to discharge, compared with 26% of such patients defibrillated by paramedics.16 During the first 5 years of the Quantas Airlines cardiac arrest program, 9% of all passengers who experienced sudden cardiac arrest and were defibrillated by flight attendants (n=22) were long-term survivors (M.F. O’Rourke, unpublished data, April 17, 1997). Early defibrillation by first aid personnel at the Melbourne Cricket Ground in Australia was associated with a survival–to–hospital discharge rate of 67% among patients with ventricular fibrillation or pulseless ventricular tachycardia (n=24) (J. Wassertheil, unpublished data, April 17, 1997). Although these studies were uncontrolled, they have demonstrated the potential benefit of expanded use of defibrillation for sudden cardiac death.
These studies are corroborated by studies of the relationship between time to defibrillation and survival in traditional EMS systems. In a pooled analysis of cardiac arrests occurring in Tucson, Ariz, and Seattle, Wash, there was no threshold below which further decreases in time to defibrillation were not associated with greater survival (T. Valenzuela, unpublished data, April 17, 1997). Recent European studies have demonstrated similar findings (M. Holmberg, unpublished data, April 17, 1997). Therefore, implementation of expanded use of defibrillation with further shortening of the time to defibrillation should be associated with increased survival regardless of the time to defibrillation in the existing EMS system.
Related work has demonstrated that most survivors of sudden cardiac arrest have acceptable quality of life and that PAD is potentially associated with an incremental cost-effectiveness ratio that is comparable to that of other common medical therapies (G. Nichol, MD, unpublished data, April 17, 1997). Collectively, this work demonstrates that PAD should be evaluated as a therapy for sudden cardiac death.
Clinical Trial to Evaluate PAD
The need for a clinical trial to evaluate the effectiveness and costs of community-based PAD should be readily apparent. In addition to answering these important clinical questions, representatives from the Food and Drug Administration have stated that a well-conducted clinical trial is essential to define appropriate usage, labeling, and approval of device(s). The trial must answer questions of effectiveness as well as documenting the potential for misapplication of the device and for undesirable outcomes. There are concerns that use of AEDs will become more widespread in many communities and may contaminate any controlled experiment. Therefore, there is some urgency to initiate a large multicenter clinical trial of PAD. The American Heart Association Task Force on Automatic External Defibrillators has proposed a study design for such a trial.
The primary hypothesis of the trial is that trained, targeted responders with a standard EMS system will increase survival–to–hospital discharge rates among patients who experience out-of-hospital sudden cardiac arrest compared with survival in a standard EMS system alone. The term “targeted responders” includes paramedical personnel and public service workers such as policemen and firemen. It may also include individuals who work or live in buildings that have a high density of individuals who are likely to be at increased risk of sudden cardiac arrest (ie, >50 years old).
Secondary questions will include whether PAD is associated with increased survival at 3 months after discharge, increased neurologically intact survival, decreased time to defibrillation, or an attractive incremental cost-effectiveness ratio compared with the standard EMS system. It is likely that there will be insufficient power to detect differences in neurologically intact survival among device-related subgroups. However, the effectiveness of individual devices may be compared in terms of an intermediate outcome, such as restoration of spontaneous circulation. Only those devices that meet FDA approval criteria will be used in the trial.
The ideal primary outcome would be 30-day survival with intact neurological function. However, it may be impractical to use this as an outcome, because individual consent would be needed to examine patients and medical records. Because informed consent may be difficult to obtain after resuscitation from sudden cardiac arrest, information about functional outcomes will be missing for some patients. If this information is missing for a large number of patients or is preferentially missing from patients enrolled in either intervention arm, then the results of the study may be biased. As an alternative, a primary outcome of 30-day survival may be supplemented by information about hospital discharge status.
Assessment of the quality of life of survivors of sudden cardiac arrest will be included in the clinical trial to demonstrate that PAD decreases morbidity as well as mortality. Once again, this may be technically difficult, given the need for informed consent. Therefore, study centers that are able to obtain more detailed quality-of-life data from survivors should be encouraged to do so as part of an ancillary study.
There are a number of logistical issues surrounding a large-scale trial in which intact social units (communities, worksites, malls, high-rise apartment buildings, etc) are the unit of randomization and analysis. A matched-pair design is proposed to allow randomization of one unit each to intervention or control status. To make placement of devices efficient, sites will have to have substantial population density within range of an available AED. This implies that sites will consist of high-density housing units or other sites where large numbers of people would gather for a sustained period of time. Within those sites, a significant event rate must occur to detect a difference between the two interventions. Available population and event rate information forms the basis of the sample size necessary for any trial. Each of these issues has been addressed in the proposed clinical trial of PAD.
Alternative numbers of study sites (20 to 50) have been considered. However, underestimation of the sample size needed and overestimation of the number of likely events is a frequent problem in clinical trial design.17 Therefore, higher numbers of randomizable sites will be considered to ensure that the study has sufficient power to detect a meaningful difference.
The generalizability of this study will depend in part on understanding the factors that contribute to effective PAD. To the extent that it is possible to do so within the context of a clinical trial, diverse sites should be selected to evaluate PAD in a variety of settings. This strategy will facilitate development of a template to describe community or site needs for successful implementation of PAD in other settings.
Issues of consent are recognized to be problematic in the setting of an unconscious and dying patient. A formal procedure has now been sanctioned by the Food and Drug Administration and Department of Health and Human Services that allows institutional review boards to waive the requirement for informed consent on such investigations. In addition, assurance of an assumption of liability will be important in obtaining participation from study sites.
The cost of PAD should be compared with that of the existing EMS system so that decision makers can determine whether early defibrillation offers sufficient value for money. However, hospital costs may be difficult to obtain without informed consent from patients. At a minimum, the costs of implementing and maintaining the defibrillation program and the duration of hospitalization of survivors should be required. More detailed information may be obtained as part of an ancillary study.
Potentially significant covariates of the effectiveness of PAD include response time intervals (such as time to defibrillation), initial rhythm, whether or not bystander CPR was instituted, and demographic variables (age, sex, ethnicity). Collection of these data will aid in the interpretation of the results of the study.
Field research conducted to date was reviewed with the intention of determining the length of training time, content, and recertification interval required. For training of targeted responders, 2 to 4 hours appears to be adequate; less may be sufficient. The core content included by most investigators is CPR and AED training. Several investigators have divided the training into two sessions, with CPR taught separately from AED use, to minimize confusion. The formal retraining interval remains unclear from the research conducted to date, but a 12-month interval appears to be adequate.
Workshop attendees concluded that the training of targeted responders should focus on psychomotor skills (eg, pad placement) and safety issues (eg, stand clear). They advocated a curriculum that was designed around goals rather than the detailed content included in current CPR training. For naive users or laypersons, the workshop attendees recommended a fixed curriculum that focuses on safety and addressed the emotional issues involved in resuscitating strangers. Psychomotor skills, knowledge, decision-making, and self-confidence issues were acknowledged to be extremely important. Time for questions and discussion of misconceptions is essential.
Interface with EMS System
With the advent of local, state, and national initiatives to implement PAD, careful consideration should be given to the interface of this new method of care with the existing EMS system. The concept of PAD takes a direction different from that of past advances in public health and safety. It will most likely involve changes to local and state EMS and medical practice acts, as well as to the traditional way that quality assurance, oversight, and monitoring is conducted. The implication is that a totally new component of the EMS system will come into existence.
By being proactive, state EMS directors can facilitate the transition toward PAD while securing a leadership role. Becoming involved in the early stages of state law modification, data coordination, and training standardization will ensure the appropriate integration.
Assistance with training of lay responders and the establishment of a protocol for turning over patients from lay responders to EMS personnel are key roles for EMS providers. Feedback for all responders, particularly stress management services for lay responders, may also be provided by EMS personnel when needed. The location of AEDs in the community should be reported to the local EMS to create a truly integrated system. Such information will be useful for planning and coordination as well as resource allocation. For best results, dispatchers should be trained to provide advice on the use of an on-site AED by a layperson.
Strong support exists for continuing the requirement of physician medical control for AEDs. Two-way communication between AED users and those who provide medical oversight is necessary to identify problems and solutions. Evaluation of PAD can be facilitated by consistent use of the National Uniform Prehospital Data Set (UPHDS, NHTSA, 1994). However, for complete evaluation of this approach, the proposed clinical trial on PAD is essential for verifying improved outcome from cardiac arrest.
Conference workshop participants made a specific recommendation that providing AED training for the formal EMS first responders who are not already trained in that skill is a first priority. The group recommended that initial PAD should focus on “targeted first responders” rather than the general public or “naive” responder.
Current AHA guidelines for pediatric resuscitation apply adult basic life support techniques and AED use to victims of prehospital cardiac arrest ≥8 years old. Although the prevalence of ventricular fibrillation appears to be lower in the pediatric population than in the adult population, high-risk subpopulations (eg, patients with congenital heart disease) can be identified. These subgroups of high-risk children and adolescents might be appropriate for inclusion in PAD programs. As in adults, promptly recognized and treated ventricular fibrillation in the pediatric population has better short- and long-term outcomes than resuscitation from asystole or pulseless electrical activity. Therefore, the use of AEDs for early identification and treatment of ventricular fibrillation is relevant to the care of pediatric cardiac arrest victims.
However, the ability of AEDs to accurately detect, analyze, and treat pediatric ventricular fibrillation and shockable ECG rhythms has not been investigated adequately in young patients. Moreover, safe and effective defibrillation doses have not been defined for AED use in children, and the potential risk of delivering excessive defibrillation suggests that safety issues be evaluated before widespread AED use is recommended for young children and infants. Therefore, children ≥8 years old should be included in a clinical trial of PAD.
Physician-scientists and representatives of the Food and Drug Administration have collaborated closely to address concerns about the feasibility of conducting clinical trials of therapies for sudden cardiac arrest with a waiver of informed consent or with deferred consent. Guidelines for conducting clinical trials dealing with therapies for medical emergencies have recently been modified (Federal Register, October 2, 1996). These new rules balance the need to provide special protection for these vulnerable subjects with the need for investigation of promising new interventions. The implication for any clinical trial of PAD is that studies involving targeted lay responders are now possible.
Physician-scientists, engineering experts, device manufacturers, and representatives of the Food and Drug Administration have also collaborated to develop guidelines for the assessment of AEDs for PAD.18 These guidelines include criteria for evaluation of the arrhythmia analysis algorithms used in AEDs, for evaluation of alternative waveforms for defibrillation, and for enhancement of safety.
Close collaboration between physician-scientists and representatives of the Food and Drug Administration will continue to ensure that the effectiveness of PAD is evaluated in a sufficiently rigorous and timely manner.
Public Policy Considerations
In April 1997, a coalition of interested parties successfully completed a 2-year effort to introduce and pass a bill allowing level 2 PAD in the state of Florida. The major elements of this bill state that physicians can prescribe an AED for use by a layperson. Laypersons can use this device to treat another person if the user is trained appropriately in CPR and in defibrillation using an AED and calls 911 as soon as possible. Laypersons are encouraged but not required to register the device with the local EMS agencies. The prescribing physician and the lay user will not be held liable if each has acted as an ordinary reasonable and prudent person. A key lesson from this successful initiative is that the coalition consisted of a broad range of representatives from EMS systems, legal representatives, the American College of Emergency Physicians, the American College of Cardiology, and the American Heart Association. Other interested parties should consider applying this model in their own jurisdiction.
At the national level, the proposed Cardiac Arrest Survival Act seeks to increase implementation of PAD. This legislation proposes to develop and disseminate a model training program for those who care for victims of sudden cardiac arrest. It also proposes inclusion of education about defibrillation in health and safety curricula. States are encouraged to incorporate defibrillation into Good Samaritan legislation to address liability concerns. Finally, a national database would be established to compare survival after sudden cardiac arrest across the United States. A federal commission would review these data and make recommendations for additional improvements to EMS systems.
In summary, clear communication about the nature of early defibrillation programs and ongoing legislation will improve our ability to implement and evaluate such programs so as to improve survival after sudden cardiac arrest.
Five recommendations were made by conference participants. First, the existing first-responder curriculum for AEDs should be reviewed. A curriculum for targeted responders should be developed by either modification of the existing curriculum for first responders or development of a new curriculum. Research training issues that should be addressed include the length of training and the retention interval. Second, inclusion of children >8 years of age as candidates for AED use by targeted responders should be considered. Third, a clinical trial is urgently needed to evaluate the effectiveness, safety, and cost-effectiveness of PAD. Such a clinical trial of PAD should include several different types of AEDs. Fourth, American Heart Association affiliates should collaborate with other interested parties to modify legislation so that early defibrillation is permissible throughout the United States. Finally, the American Heart Association, American College of Cardiology, National Heart, Lung, and Blood Institute, state EMS directors, representatives of the Food and Drug Administration, and other interested parties should have an ongoing discussion about the implementation and safety of early defibrillation.
Selected Abbreviations and Acronyms
|AED||=||automatic external defibrillator|
|EMS||=||emergency medical services|
|PAD||=||public access defibrillation|
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- Copyright © 1998 by American Heart Association
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