Cardiac Arrest

The Approach to Out-of-Hospital Cardiac Arrest: The Role of Automated External Defibrillators

Thomas Hartka, MD, MS, William J. Brady, MD

Volume 55 - Issue 7 - July 2015

ABSTRACT: Cardiac arrest is generally associated with a poor prognosis, which is only exacerbated in an out-of-hospital setting. Therapeutic interventions may be abbreviated and less complex than in-hospital treatment, but are still vital to survival and include recognition of the event, activation of the emergency response team (ie, calling 911), cardiopulmonary resuscitation (particularly chest compressions), and use of automated external defibrillators (AEDs). The prognosis can be improved through an early response on site prior to the arrival of the emergency response team. This conclusion to this 2-part series will summarize the role of AEDs in cardiac care. 

 

There were an estimated 359,400 incidences of out-of-hospital cardiac arrest (OHCA) in the United States in 2012.1 There may be few or no warning signs before the onset of cardiac arrest. As a result, survival from OHCA is typically low and largely impacted by the location of the arrest event.2 Despite advances in cardiac resuscitation, there has been little improvement on the rate of survival from OHCA in the last 30 years.

In 1995, the American Heart Association (AHA) proposed the concept of chain of survival—a sequence of events that should be executed in the shortest possible time in order to maximize survival from OHCA. The first 3 links to the chain include early notification to emergency medical services (EMS), bystander cardiopulmonary resuscitation (CPR), and early defibrillation. 

The first half of this 2-part series discussed the role of the emergency response team and the importance of beginning CPR. This conclusion will discuss the use of automated external defibrillators (AEDs), including background information, survival rates with AED use, implementation steps, and associated costs and liability.  

Understanding Cardiac Activity

The victim of cardiac arrest has insufficient mechanical cardiac activity to sustain an adequate blood pressure. 

There are 4 main potential underlying cardiac rhythms during cardiac arrest: 

•Asystole is the absence of detectable electrical activity of the heart.

•Ventricular fibrillation (VF) is disordered electrical activity of the ventricles that produces rapid, unsynchronized contractions. 

•Ventricular tachycardia (VT) is rapid, synchronized heart contractions that originate from the ventricles. 

•Pulseless electrical activity (PEA) refers to organized electrical signals that do not result in sufficient mechanical activity to produce a detectable blood pressure. In PEA, the heart may produce electrical signals that are indistinguishable from normal cardiac activity, however, there is no palpable pulse. 

VT and VF are unique because the heart is producing electrical signals, but the electrical activity is disordered. The heart may have the potential to produce adequate blood flow if normal electrical activity is restored. A defibrillator delivers an electric shock, which changes the transmembrane potential of the myocytes. If a large enough percentage of the heart tissue is simultaneously depolarized, it will be temporarily refractory to electrical impulses.3 In essence, the heart is temporally stunned. The intrinsic pacemaker cells of the heart then spontaneously begin producing electrical impulses. The anticipated benefit is that the electrical activity will return to a normal organized impulse originating from the atrium. 

Delivering a defibrillation shock to heart rhythms other than VT and VF is not beneficial and may be detrimental. For instance, if a defibrillation shock is delivered near the end of a normal electrical impulse (during the T wave), there is the potential to induce VF or VT. This is known as the R-on-T phenomenon.4 

Defibrillation shocks delivered during asystole are not beneficial since there is no spontaneous electrical activity of the heart and these shocks may cause myocyte injury. Additionally, any unnecessary interruptions to CPR decrease a patient’s chance of survival.4

The Role of AEDs

AEDs are self-contained devices that are able to automatically analyze heart rhythms of victims of cardiac arrest and deliver electric shocks if appropriate. AEDs have been proven to substantially increase survival from cardiac arrest in many different environments.5-9

In 1979, Diack et al published a paper describing their development of the first publically available AED10; the defibrillation unit was connected to the patient by electrodes attached to the tongue and chest. The early AED determined if a shock was appropriate based solely on heart rate.11 Since the initial model, AEDs have become much more sophisticated in their heart rhythm analysis algorithms and both of the electrodes have been moved to the chest. Modern devices consist of a single processing and defibrillating unit with 2 electrodes that are placed in contact with the patient.

Public access defibrillation (PAD) refers to AEDs available for use on persons in cardiac arrest in nonpatient care areas.8 The AHA recommends that PADs be available in high-density areas—such as airports, casinos, shopping malls, and major-sporting venues.

Survival Benefit of AEDs

A study of 6789 hospitalized patients at multiple medical centers compared survival among patients with a shockable rhythm (VF or pulseless VT) immediately after arrest. When defibrillation was delayed >2 minutes, survival decreased from 39.3% to 22.2%. In survivors, discharge with no major neurologic disability was decreased from 60.1% to 51.7% with delayed defibrillation. For each minute of delay to defibrillation, there was decrease in survival to hospital discharge.12

Similar increases in survival are seen with decreased time to defibrillation outside of the hospital. A study of 1667 patients with witnessed collapse who were found to have VF by EMS personnel found that survival decreased as time to defibrillation increased. This model showed a 7% to 10% decrease in survival for every minute of delay to defibrillation if CPR was not performed. If CPR was immediately initiated, survival decreased at a slower rate of 3% to 4% per minute.5

Data showing improvements in survival with early defibrillation led to initiatives to make AEDs widely accessible. In 1995, the AHA recommended PAD programs as a method to improve survival from OHCA.13 In a 2000 study, AEDs were placed on the premises of several Las Vegas casinos and security guards were trained in AED usage. The data showed an impressive 59% survival to hospital discharge in patients found to be in VF arrest. In this study, defibrillation was provided on average 4.4 minutes after collapse. When defibrillation was performed within 3 minutes, survival was 74%. By comparison, survival decreased to 49% when defibrillation occurred >3 minutes after collapse.14 

Similarly, in 2002, a 2-year prospective trial followed AED placement in Chicago airports.6 This study differed from previous interventions in that AEDs were placed in public locations and were intended for use by the public. During the study period, AEDs were used on 26 people thought to be experiencing OHCA. Of these 26 people, 20 were found to be in cardiac arrest. Of the 20 cardiac arrests, 18 were found to be in VF and 2 in PEA. All 18 patients in VF were correctly identified by the AEDs and defibrillation shocks were administered. The end result: 11 patients regained consciousness and survived to hospital discharge (survival from cardiac arrest was 55%).6 Note: Although there was no data for comparison from the pre-invention period, survival from cardiac arrest to hospital discharge was 2% in a previously conducted study in the Chicago Metropolitan area.15

Increased survival with immediateAED response has also been shown in community-based interventions. A large, multicenter study included 19,000 volunteers (no emergency medical care personnel) who receive training solely in CPR or CPR and AED usage and 993 community locations (including shopping malls, recreation centers, hotels, and apartment complexes).9 Each of the volunteers was randomized to 1 of the 2 training groups. Among victims of witnessed OHCA, survival to hospital discharge was 14% in the CPR-only group. In the group of patient treated by responders trained in CPR and AED usage, survival was increased to 23%. 

In an analysis of a 2010 nationwide AED initiative, Kitamura et al5 compared outcomes for all witnessed OHCA victims. For patients found to be in VF, survival at 1 month increased from 14.4% to 31.6% when shocks were administered from an AED. 

Implementation of AED Programs

In 2012, Whitney-Cashio et al8 published a review of their experience implementing a PAD program at the University of Virginia (UVA). They recommended a stepwise approach to establishing a PAD program, including the following key points: 

•Obtain institutional leadership approval and support. This is important as endorsement from leadership is necessary for funding and for acceptance by members of the institution. 

•Enlist appropriate personnel to oversee and implement program. The minimum recommended personnel include a medical director, program coordinator, local site AED coordinators, and CPR/AED training facilitators. The medical director should be a trained physician or medical authority who can oversee the entire program.

•Identify current resources. In a large organization, it is not uncommon for individual departments to have purchased AEDs independently. These smaller PAD programs are likely to have varied AED types, non-strategic placement, and lack of central coordination and medical oversight.8 

•AED deployment. UVA chose to implement their institution-wide, coordinated program in a phased approach.8 AEDs were initially deployed with the university police force due to their rapid response to all emergencies. This is similar to the initial PAD programs that targeted security guards.13

•Integrating with local public safety agencies. Security and police may have response times that are longer than optimal, especially in areas that are difficult to access. However, since the breadth of their area of response usually cover the entire institution, they provided the best opportunity for complete AED coverage in a limited implementation.

•Centralize AED program. The next phase of the UVA implementation was to develop a centralized program to coordinate existing AEDs programs. This includes creating uniform medical oversight and possible standardization of AED unit types.

Site Selection and Integration 

AED site selection is a complex issue and no formal guidelines exist for recommended placement. Building and area selection should be made on the basis of number of at-risk individuals, amount of foot traffic, local interest in the program, and difficulty of access by public safety responders.9 

Placement within a building or designated area requires many site-specific considerations. AEDs should be placed in areas that are highly visible and accessible at all times (within 3 minutes foot response area). When possible, it is recommended to place AEDs near existing emergency equipment. It is also important to work with individuals who regularly use an area to determine placement consistent with normal functioning of a building as well as to identify areas of special aesthetic and historical importance. 

Once selected, the location of AEDs needs to be communicated to local public safety agencies and regular maintenance should be performed.8 A site coordinator should do a daily confirmation that the AED is present, the functionality of the AEDs should be reviewed weekly, and the battery and pads should be checked monthly. The site coordinator should also be responsible for determining if there are sufficient employees trained in AED usage and if training is up to date.

Cost, Complications, and Liability 

The cost of instituting PAD program depends on a variety of factors. Costs include the AED unit, replacement batteries and pads, AED housing, installation, and user training. The cost of a self-contained unit varies based on manufacturer and display type. In 2013, prices typically ranged from $1000 to $3000. The cost of PAD AED program is usually calculated as the yearly cost per life saved, or alternatively as cost per quality-adjusted life-year (QALY). These cost analyses are dependent on the concentration of people in the program area and the probability of an OHCA in the population. 

In 2002, Caffery et al determined the cost of implementing PAD programs in 3 airports to be an average of $35,000 per year over a 10-year period. This correlated to a cost $7000 per year per life saved.6 Due to density of travelers and high rate of cardiac events in the airports, these costs are significantly lower than would be expected in most areas. In a separate study examining the results of a large-scale community PAD implementation, the mean cost per QALY was calculated at $68,400 for locations supplied with CPR training and AEDs. By comparison, the mean cost per QALY was $42,400 in locations with CPR-only training. However, the rate of survival to hospital discharge from cardiac arrest in the CPR-only group was less than half the survival rate in locations with an AED.16 

AED has been shown to be safe and effective, even when used by someone not trained on the equipment. In the aforementioned study of AED placement at Chicago airports, 6 out of 11 survivors were defibrillated by a member of the public who had never operated an AED previously and were not formally trained in their use.6 There were no inappropriate shocks delivered during the study. For modern AEDs, the sensitivity for detecting shockable rhythms and the specificity for delivering shocks only when indicated is nearly perfect. In an OHCA study, 44 shocks were delivered by non-EMS AED.7 Of these 44 shocks, none were delivered inappropriately based on subsequent review of the AEDs cardiac rhythm recordings. In their most recent guidelines, the AHA goes so far as to recommend that AED use should not be restricted to trained personnel.17

Medicolegal accountability is an important issue when instituting a PAD program. In all 50 states, the Good Samaritan law protects persons acting in good faith as long as the rescuer does not engage in gross negligence or misconduct and the rescuer does not receive compensation. All states now extend the Good Samaritan law to include AED usage. Furthermore, the Cardiac Arrest Survival Act of 2000 provides some limitations to liability to persons using an AED and those involved in purchasing AEDs. Most states also provide some degree of protection for AED purchasers and those associated with the PAD program. There may be potential for liability due to acts of omission and not having a program in place to provide AEDs, which is not address under current legislation.18 Legal council should be obtained regarding specific state protections and responsibilities.

We now know that cardiac arrest should be assumed in any situation in which a person is seen to collapse or found unconscious. Identification of cardiac arrest is complicated as other conditions (eg, intoxication, hypoglycemia, syncope, and postical state) are also potential causes for unresponsiveness.19 However, with timely execution, the first 3 links in the chain of survival significantly improve the patient’s final outcome. 

Thomas Hartka, MD, MS, is an assistant professor and assistant research director in the department of emergency medicine at the University of Virgina. He also serves as the assistant medical director at the Center for Applied Biomechanics and performs research in prehospital resuscitation training. 

William J. Brady, MD, is a professor of emergency medicine and medical director of emergency preparedness and response at the University of Virginia and operational medical director of Albemarie County Fire Rescue. He is active clinically in emergency medical care at the University of Virginia and the surrounding region. 

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