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Do AEDs work all the time?

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Unfortunately, AEDs will not always be able to save a victim of Sudden Cardiac Arrest (SCA). However, the availability and use of an AED will increase the odds of survival in these medical emergencies.

What is SCA and how can AEDs help?

SCA is when the heart stops pumping blood though the body. The organs in our body need oxygen from blood to do their jobs, and when they are deprived of oxygen they start to fail and die. This is why it is important to try and get the heart pumping blood properly again as soon as possible.

AEDs start their work by analyzing the electrical rhythm of the patient’s heart. There are several different types of SCA, and the AED will figure out what kind of SCA the patient is experiencing and determine if the condition is “shockable” or “non-shockable.” If it is a “shockable” condition, the AED has the ability to give the patient a shock (also called defibrillation) that can help reset the heart’s electrical rhythm back to normal, which may allow the heart to start beating effectively again.  If the patient’s condition is considered to be “non-shockable” the AED will not recommend a shock. The fact that some patients cannot be helped with a shock is an inherent limitation to the AEDs effectiveness. However, keeping the AED attached to the patient is important because it can continue to provide instructions, monitor the heart, and provide a shock if the heart rhythm changes into one of the shockable rhythms.

Surviving SCA

Sudden cardiac arrest is the most severe of all medical emergencies and sadly the rates of survival are low. Only 10.6% of people who experience SCA outside of a hospital survive to the point where they can be discharged from the hospital, but not all of these patients are considered to be “neurologically intact.” The loss of oxygen to the brain that occurs during cardiac arrest can cause permanent damage. Only 8.3% of people who suffer SCA outside a hospital are discharged without significant neurologic damage. While the survival statistics for an out-of-hospital SCA event may seem abysmally low, the survival rate of SCA that occurs in the hospital when the patient is surrounded by trained medical professionals who can provide immediate high quality care is only 25.5%.

So why is it that some people survive SCA while others do not? Why is it that an AED cannot revive every victim of cardiac arrest? Part of the answer has to do with the “non-shockable” rhythms described above. Because defibrillation is not able to bring a heart back from these conditions, and as a result the fatality rate is significantly higher than people who present with a “shockable” rhythm. Time is another major factor that influences SCA survival, and we will discuss that in more detail below. The unfortunate fact is that some people are alone when they experience cardiac arrest, and by the time they are found there has been too much damage to their heart, brain, and other organs for it to be possible to survive. Finally, the cause behind the SCA must be considered. If, for instance, the cardiac arrest was secondary to a large heart attack, the heart muscle may be too damaged to respond to the defibrillation or other treatments.

Despite all the disheartening statistics, there are several factors that can contribute to helping someone survive SCA.


Did you know that CPR was developed all the way back in 1960? The way we perform CPR has changed a bit through the years as new research allowed us to refine the technique to obtain the best outcomes. The American Heart Association (AHA) recommends that CPR be started as soon as a person collapses and continues until an AED is available and ready to use, EMS arrives to take over, or until the victim starts moving on their own. Ideally a rescuer is trained in effective CPR methods, either through a Basic Life Support (BLS) or Advanced Cardiac Life Support (ACLS) class. However, even an untrained bystander is encouraged to start pushing hard and fast on the center of a victim’s chest immediately after they call 911. These chest compressions help perform the heart’s normal function of moving blood through the body. Keeping the blood flowing will help get some oxygen to the body’s essential organs. Not only will this help increase the victim’s odds of survival, but it will help to prevent brain damage in survivors.


The use of an AED can greatly improve the rate of survival in cases of SCA, especially when it is used quickly. On average it can 8 to 12 minutes for first responders to arrive after a call is placed to 911. However, the chance of survival decreases 10% each minute that a patient in a shockable rhythm goes without defibrillation.

A study published in 2010 observed emergency medical services (EMS) sites across the Unites States and Canada and found that having an AED nearby nearly doubled the rate of survival. A similar study published in 2011 and conducted in Europe estimated that an onsite AED shortened the time to the first shock by approximately 7 minutes. This study also found that the use of an onsite AED doubled the rate of survival of patients who experienced cardiac arrest outside of a hospital.  While there is no guarantee that an AED will help a patient survive this type medical emergency, it is evident that quick access to a nearby AED is a very important factor in helping people survive cardiac arrest.

Public Access Defibrillation (PAD) Programs

Given that AEDs are so important to helping a victim survive SCA, it’s a good idea to know where you can find an AED in the case of an emergency. After all, an AED can’t do its job if it’s not even available to the rescuer! Not every state has laws that mandate the placement or AEDs. In fact, only a few states require the placement of AEDs in locations such as schools, health clubs, or swimming pools. The AHA recommends placing AEDs in public and private areas “where large numbers of people gather or where people who are at high risk for heart attacks live.” These locations include schools, sport complexes and gyms or health clubs, apartment complexes and gated communities, doctor’s offices, business offices, shopping malls, or places of worship, just to name a few.

The Department of Health and Human Services (HHS) and General Services Administration (GSA) has guidelines for PAD programs in Federal facilities. Their statements regarding the recommendation of the placement of AEDs could be useful for any organization or business looking to implement an AED program. The key points include:

  • An optimal response time is 3 minutes or less. Multiple AEDs placed in different locations may be required for large buildings or campuses with multiple buildings.
  • The AED should not be obstructed, and should be placed low enough so that people of shorter stature can reach the AED.
  • Consider a location that will minimize the risk of tampering or theft of the AED.
  • The AED’s location should be well marked and known to all people who are trained to use the AED.
  • Automatic Notification of EMS. Ideally the AED should be located in a cabinet that automatically notifies EMS when it is opened. If this is not possible, consider placing the AED near a telephone and emphasize the importance of proper notification in the PAD program’s protocol.

AED Maintenance

An AED can’t play its critical lifesaving role if it isn’t in proper working condition. An important part of every PAD program is making sure the AED is maintained. The AHA recommended that PAD programs designate a person to perform weekly or monthly visual inspections of the AED, and that this person develops a written checklist to ensure that the AED and its supplies are ready for use in an emergency. These inspections should be performed in addition to more detailed maintenance inspections that are recommended by the device’s manufacturer. It is also important for your manufacturer to inform you when there are software updates for your specific device and for those upgrades to be made to your machine.


Berdowski J, Blom MT, Bardai A, et al. Impact of onsite or dispatched automated external defibrillator use on survival after out-of-hospital cardiac arrest. Circulation. 2011; 124:2225-2232.

Weisfeldt ML, Sitlani CM, Ornato JP, et al. Survival after application of automatic external defibrillators before arrival of the emergency medical system. J Am Coll Cardiol. 2010; 55(16):1713-1720.

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