The American Heart Association (AHA) identified several key principles, or processes, that improve survival of out of hospital cardiac arrest (OHCA).  These principles are described as "links" in the "OHCA chain of survival."  The first three links in the OHCA chain of survival are early recognition and activation of the emergency response system, providing early cardiopulmonary resuscitation (CPR), and rapid defibrillation. Survival and subsequent neurologic recovery following an OHCA are dependent on multiple factors. Per review of OCHA literature, predictors of survival include[1]:

• Witnessed arrest
• Availability of bystander CPR
• Having a shockable initial rhythm (ventricular tachycardia or ventricular fibrillation)

There is an association between a patient achieving return of spontaneous circulation (ROSC) in the field and improved neurologic outcome. The location of a patient’s cardiac arrest is an important factor in their survival. Over seventy percent of OHCAs occur in a private residence, and unfortunately, less than ten percent survive to hospital discharge. Approximately 20% of OHCAs occur in public places.[2]  Literature has supported improvements in cardiac arrest survival rates with the performance of bystander CPR. CPR can prevent the degradation of a shockable rhythm to a non-shockable rhythm. Improved quality of life and health outcomes have been demonstrated in those who received bystander CPR compared to those who did not.[3] A study in New Zealand suggests that cardiac arrests occurring in public are twice as likely to survive to discharge.[4] Arrests occurring in public are more likely to be witnessed and benefit from bystander CPR and early defibrillation.

The placement and use of automated external defibrillators (AED) in public locations with an emergency response plan in place have been shown to double a patient’s odds of survival from cardiac arrest.[2]

Cardiac arrests caused by shockable arrhythmias such as ventricular fibrillation and ventricular tachycardia can be treated with an electrical shock by an AED. Most cardiac arrests that occur in public areas are due to ventricular fibrillation.[5] Bystander CPR can extend the window for defibrillation; however, defibrillation is the definitive way to reverse the arrhythmia. Early use of CPR and AED in patients with ventricular fibrillation can have a survival rate between 40 and 75 percent. Unfortunately, AEDs are rarely immediately available and if so are used by bystanders only in up to 4% of cases.[2]

Public access to defibrillation (PAD) programs has been created across the United States. PAD programs are intended to improve OHCA survival by increasing the likelihood that a bystander can access an AED, apply an AED, and provide early defibrillation when needed. Many PAD programs have been implemented worldwide. There have been statistically significant improvements demonstrated in federal buildings, airports, casinos, fitness centers, churches, schools, and workplace environments. Survival rates vary between 28 and 56 percent. OHCA patients have significantly better outcomes when the first shock is provided by a bystander before EMS arrival.[6]

Placement of an AED in a public location is warranted if[7][8][9]:

• Greater than 250 adults older than the age of 50 access the location over 16 hours per day
• High-risk location of presence of high-risk individuals
• Gyms with more than 2500 members
• Cardiac arrest event at the location at least every few years

Some areas of concern for PAD programs are:

CostPAD programs can be cost-effective, with cost per-quality-adjusted -life-year ranging from 30000 to 100000, an acceptable range for many medical therapies.[10][11][12][13] However, PAD programs are less cost-effective when AEDs are placed in programs without adequate support or EMS integration.[14] The cost of AEDs is sometimes prohibitive for locations such as schools.

Locating AEDs in publicAirports publicly display AEDs throughout terminals. However, some locations keep the device out of view. Knowing that a location has an AED does not help you find the device. Some buildings will keep the AED in a locked box with security or will hang the device without identification. There is no national registry to track AEDs, despite the purchase of one million devices over the last 20 years.[15][16]

Reluctance to implementFear of litigation, training personnel, developing facility-specific response plans, and around the clock response capability are all barriers to implementing programs. Some barriers to implementing PAD programs in schools include funding, balancing time for training with scholastic requirements, course content, and lack of equipment.[2]

The reluctance of the public to act in an emergencyIf a PAD program is available, individuals must be willing to use the AED. Many people are concerned about legal liabilities, limited knowledge, low rates of training, and limited access. Many AEDs are stored in cases that state the device is for trained professional use only, which can be a major deterrent to an untrained bystander. Congress passed the Cardiac Arrest Survival Act of 2013 which recommends that all US federal government buildings develop AED programs; this also provides limited immunity from civil liability for the user if the state has not otherwise granted it; every state now has instituted protection under the Good Samaritan laws for bystanders who use AEDs.[7]

AED adverse eventsAdverse events include theft of the device, placement in inaccessible locations, improper maintenance, and mechanical challenges.[17]

The timely use of AEDs by bystanders has been consistently demonstrated to be effective in improving OHCA. This makes AED use one of the most beneficial interventions known for cardiac arrests secondary to a shockable rhythm. PADs can substantially reduce the time to defibrillation, particularly in the United States when EMS response time from to dispatch to scene for an adult arrest is on average 9.4 minutes.[2] Survival rates for witnessed OHCA with ventricular fibrillation decreases by 3 to 4% for every minute that passes between collapse and defibrillation.[18][19] The audible instructions provided by the AED can help provide life-sustaining support until EMS arrives, even for those with non-shockable rhythms.

Data from the ARREST study indicated that when the location of a public AED was promoted, the use of the AED increased threefold.[20] The PAD trial in 2004 delivered a structured and monitored emergency response system involving lay volunteers in both CPR or CPR and use of AED to community units such as shopping malls and apartment complexes. There were more survivors to hospital discharge in the units assigned to have volunteers trained in both CPR and the use of AEDs.[21] A study performed in Chicago installed AEDs at regular intervals in passenger terminals at airports. Promotion of the use of the devices was by videos, pamphlets, and media reporting. Over a two-year period, 21 patients had a non-traumatic cardiac arrest, 18 of which were in ventricular fibrillation. Eleven of these patients were successfully resuscitated. Six of the 11 rescuers had no prior training or experience in the use of AEDs.[22]

AEDs save lives – they need to be available, and people need to know how to use them. Improving outcomes starts by instilling a culture of action. Culture change can occur early, by having CPR and AED classes in schools. Third-grade students have been shown to use AEDs effectively. Sixth-grade students have demonstrated AED competence similar to EMS providers.[23][24] Using social media and crowdsourcing is a way to increase knowledge of AED locations, as shown with the My Heart Map Project.[25] AED locations would benefit from being added to a national registry. Changing perspectives on AED use might occur if it were made a public health initiative, much like seat belts, airbags, fire extinguishers, and sprinkler systems.

In summary, the three essential elements for a successful PAD program include[12]:

• Establishing a functional and practiced internal emergency response plan
• Offering adequate training for CPR and AED use
• Integrating with local EMS