Out-of-hospital cardiac arrest (OHCA) is a leading cause of death in the industrialized world. The global average incidence is 55 adult OHCAs of presumed cardiac cause per 100,000 person-years, of whom on average 7% will be discharged alive from the hospital.⁽¹⁾ Many OHCAs are precipitated by lethal heart arrhythmias (ventricular fibrillation or pulseless ventricular tachycardia) that can be reversed only by the shock with a defibrillator. The sooner the shock is delivered, the higher the probability the victim will survive the event. Without treatment, the chance of survival from OHCA decreases by 7% to 10% for every minute of delay.⁽²⁾ To improve survival after an OHCA, early defibrillation by laypersons using an automated external defibrillator (AED) play a key role in the “chain of survival”.⁽³⁾

Previous recommendations of the American Heart Association and International Liaison Committee on Resuscitation support the idea that defibrillators should be widely available and accessible.^(4,5) This raises the question whether all schools⁽⁶⁾ and workplaces should have AEDs.

AEDs are designed for use by non-medical personnel so that defibrillation can be delivered before emergency medical services (EMS) personnel arrive at the scene. There are two ways of making an AED available to cardiac arrest victims. First, AEDs can be placed at a specific location like the school or workplace (onsite AED). In this setting, the AED will only be used on patients who suffer their cardiac arrest at the site of the AED. Second, EMS services may dispatch first responders like fire fighters or policemen with an AED to the scene of the cardiac arrest (dispatched AED programs). In this setting, the AED can cover a much larger area and thus serves a broader public.

Clinical Data

Small studies conducted around the introduction of AEDs in specific study locations like casinos⁽⁷⁾ and airports⁽⁸⁾ have shown high survival rates for patients with a shockable initial rhythm, ranging from 53% to 61%.

The outcomes of dispatched AED studies were not all equally promising. Although observational studies showed dispatched AED use tripled survival rates in comparison to historical controls,^(9,10) a randomized controlled clinical trial with initial random allocation of AEDs to first responders showed no significant survival benefit. ⁽¹¹⁾ Until recently, clinical data from a ‘real world’ setting showing the survival benefit of onsite and dispatched AED use have been lacking.

A recent Dutch observational cohort study showed the effectiveness of the AED is mainly determined by the time interval between the collapse of the patient and the first shock given.⁽¹²⁾ Onsite AED use significantly reduced the time to first shock from 11 minutes to 4.1 minutes. Survival with minimal neurologic impairment was 49.6% for patients treated with an onsite AED against 14.3% for those without AED treatment. Dispatched AED use only showed a marginal survival benefit due to a limited reduction in time to shock (11 to 8.5 minutes), observed at the end of the survival window. However, both onsite AEDs and dispatched AED programs have proven to effectively increase survival rates in public locations (adjusted odds ratio 3.40; 95% CI, 2.12-5.44 and 1.88; 95%CI, 1.18-3.00, respectively).

Optimal Placement of AEDs

Public-access defibrillation programs require strategic placement of defibrillators where the risk of cardiac arrest is high. The AHA proposes AED placement in areas with at least 1 cardiac arrest every 5 years.⁽¹³⁾ A recent Danish study showed that if public-access defibrillation programs are to improve survival in the community, the AEDs must cover the greatest possible number of cardiac arrests occurring in public.⁽¹⁴⁾ A cardiac arrest was ≈5 to 8 times more likely to occur at train stations, ferry terminals, or high-density public areas than areas without such characteristics, like schools or large industrial businesses. These findings emphasize that parameters such as the number and characteristics of visitors (with the same lower limit of more than 250 people over the age of 50 present for more than 16 hours a day) also need to be taken into account for optimal placement of AEDs.⁽¹⁵⁾

To place an AED at every school is debatable, since the age group of students is associated with a relatively low risk of OHCA. In schools in Seattle and King County, WA,⁽¹⁶⁾ cardiac arrest occurred on average in ≈1 of 111 schools annually, with a greater incidence among colleges (1 OHCA per 8 colleges) than among high schools (1 per 125 high schools) or lower-level schools (1 OHCA per 200 preschools through middle schools). Only 12% of the OHCAs were among students; the majority of cases were among faculty and staff (34%), and among adults not employed by the school (46%).

Placing defibrillators in the workplace is just as controversial, because cardiac arrest rarely occurs in this setting. Depending on the definition of “workplace”, the reported proportion of OHCAs occurring in that setting was 1-6%.^{(12, 17-24)} Despite its relatively low incidence, several authors have reported that patients who experience OHCA in the workplace have a relatively high survival rate.^(15,16) The Resuscitation Outcome Consortium showed that survival after OHCA in a workplace increased even more (from 15% to 22%) if an AED had been used.⁽²²⁾ These impressive survival rates have been attributed to a high percentage of bystander witnessed collapse and CPR.⁽²¹⁾ Effective CPR slows down deterioration of ventricular fibrillation,⁽²³⁾ prolonging the window of opportunity for successful defibrillation.⁽²⁴⁾

Costs

If money were no object, every school and workplace should have one or more AEDs, depending on the size of the premises. The closer the AED is located to the potential victim, the shorter the time to shock, and the higher the chances of survival. Because an OHCA is relatively rare in the workplace and school, defibrillators might not be cost effective in these settings. Aside from the purchase of the AED(s), the device(s) need to be maintained, and potential lay rescuers need to be trained in basic life support techniques and AED use on a regular base. These issues need to be implemented in a coordinated and practiced emergency response plan.⁽²⁵⁾ This plan must start with development of a good system of communication, and requires development and coordination of a planned and practiced response, and risk reduction.

The findings of the recent Dutch study⁽¹²⁾ should encourage communities worldwide to explore which AED program is optimal for their situation, taking into account the incidence and risk factors of cardiac arrest at the location, financial means and the time it takes emergency teams to arrive at the scene.

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References

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Keywords: Arrhythmias, Cardiac, Defibrillators, Electric Countershock, Out-of-Hospital Cardiac Arrest, Probability, Tachycardia, Ventricular, Ventricular Fibrillation

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