automated external defibrillator, open and ready for
pads to be attached
automated external defibrillator (AED) is a portable
device that automatically diagnoses the life threatening
fibrillation and ventricular
tachycardia in a patient,
and is able to treat them through defibrillation,
the application of electrical therapy which stops the arrhythmia,
allowing the heart to reestablish an effective rhythm.
simple audio and visual commands, AEDs are designed to be
simple to use for the layperson,
and the use of AEDs is taught in many first
responder, and basic
life support (BLS) level cardiopulmonary
resuscitation (CPR) classes.
that the device treats
automated external defibrillator
is used in cases of life threatening cardiac arrhythmias
which lead to cardiac
arrest. The rhythms that the device will treat are usually
each of these two types of shockable cardiac
arrhythmia, the heart is electrically active, but in
a dysfunctional pattern that does not allow it to pump and
circulate blood. In ventricular tachycardia, the heart beats
too fast to effectively pump blood. Ultimately, ventricular
tachycardia leads to ventricular fibrillation. In ventricular
fibrillation, the electrical activity of the heart becomes
chaotic, preventing the ventricle
from effectively pumping blood. The fibrillation in the
heart decreases over time, and will eventually reach asystole.
like all defibrillators, are not designed to shock asystole
('flat line' patterns) as this will not have a positive
clinical outcome. The asystolic patient only has a chance
of survival if, through a combination of CPR and cardiac
stimulant drugs, one of the shockable rhythms can be
established, which makes it imperative for CPR to be carried
out prior to the arrival of a defibrillator.
of delayed treatment
these cardiac conditions (ventricular tachycardia, ventricular
fibrillation, asystole) rapidly lead to irreversible brain
damage and death, once cardiac arrest takes place. After
approximately three to five minutes in cardiac arrest,
irreversible brain/tissue damage may begin to occur. For
every minute that a person in cardiac arrest goes without
being successfully treated (by defibrillation), the chance
of survival decreases by 7 percent per minute in the first
3 minutes, and decreases by 10 percent per minute as time
advances beyond ~3 minutes.
are designed to be used by laypersons who ideally should
have received AED training. However, sixth-grade students
have been reported to begin defibrillation within 90 seconds,
as opposed to a trained operator beginning within 67 seconds.
This is in contrast to more sophisticated manual and semi-automatic
defibrillators used by health
professionals, which can act as a pacemaker
if the heart rate is too slow (bradycardia)
and perform other functions which require a skilled operator
able to read electrocardiograms.
with a metal underwire
and piercings on the torso must be removed before using
the AED on someone to avoid interference.
American TV show Mythbusters
found evidence that use of a defibrillator on a woman wearing
an underwire bra can lead to arcing or fire but only in
unusual and unlikely circumstances.
study analyzed the effects of having AEDs immediately present
during Chicago's Heart Start program over a two-year period.
Of 22 individuals 18 were in a cardiac arrhythmia which
AEDs can treat (Vfib or Vtach). Of these 18, 11 survived.
Of these 11 patients, 6 were treated by good Samaritan bystanders
with absolutely no previous training in AED use.
AED at a railway station in Japan.
external defibrillators are generally either held by trained
personnel who will attend events or are public access units
which can be found in places including corporate and government
offices, shopping centres, airports, airplanes,
sports stadium, schools and universities, community centers,
fitness centers, health clubs, theme parks, workplaces and
any other location where people may congregate.
Medical Center in Borough
was the first hospital in the United States to implement
fully automated external defibrillators at the bedside.[citation
location of a public access AED should take into account
where large groups of people gather, regardless of age or
activity. Children as well as adults may fall victim to
sudden cardiac arrest (SCA).
many areas, emergency vehicles are likely to carry AEDs,
with some ambulances carrying an AED in addition to manual
defibrillators. Police or fire vehicles often carry an AED
responder use. Some areas have dedicated community first
responders, who are volunteers tasked with keeping an AED
and taking it to any victims in their area. AEDs are also
increasingly common on commercial airliners, cruise ships,
and other transportation facilities.
buildings are densely populated, but are more difficult
by emergency crews facing heavy traffic and security barriers.
It has been suggested that AEDs carried on elevators could
save critical minutes for cardiac arrest victims, and reduce
their deployment cost.
order to make them highly visible, public access AEDs are
often brightly colored, and are mounted in protective cases
near the entrance of a building. When these protective cases
are opened or the defibrillator is removed, some will sound
a buzzer to alert nearby staff to their removal, though
this does not necessarily summon emergency services; trained
AED operators should know to phone for an ambulance when
sending for or using an AED. In September 2008, the International
Liaison Committee on Resuscitation issued a 'universal
AED sign' to be adopted throughout the world to indicate
the presence of an AED, and this is shown on the right.
trend that is developing is the purchase of AEDs to be used
in the home, particularly by those with known existing heart
The number of devices in the community has grown as prices
have fallen to affordable levels. There has been some concern
among medical professionals that these home users do not
necessarily have appropriate training,
and many advocate the more widespread use of community responders,
who can be appropriately trained and managed.
an AED kit will contain a face
shield for providing a barrier between patient and first
aider during rescue breathing; a pair of nitrile
rubber gloves; a pair of trauma
shears for cutting through a patient's clothing to expose
the chest; a small towel for wiping away any moisture on
the chest, and a razor for shaving those with very hairy
manufacturers recommend checking the AED before every period
of duty or on a regular basis for fixed units. Some units
need to be switched on in order to perform a self check;
other models have a self check system built in with a visible
manufacturers mark their electrode pads with an expiration
date, and it is important to ensure that the pads are in
date. This is usually marked on the outside of the pads.
Some models are designed to make this date visible through
a 'window', although others will require the opening of
the case to find the date stamp.[citation
is also important to ensure that the AED unit's batteries
have not expired. The AED manufacturer will specify how
often the batteries should be replaced. Each AED has a different
recommended maintenance schedule lined out in the user manual.
Common checkpoints on every checklist, however, also include
a monthly check of the battery power by checking the green
indicator light when powered on, condition and cleanliness
of all cables and the unit, and check for the adequate supplies
use of easily visible status indicator and pad expiration
date on one model of AED
AED is external because the operator applies the
electrode pads to the bare chest
of the victim, as opposed to internal
defibrillators, which have electrodes
surgically implanted inside the body of a patient.
refers to the unit's ability to autonomously analyse the
patient's condition, and to assist this, the vast majority
of units have spoken prompts, and some may also have visual
displays to instruct the user.
turned on or opened, the AED will instruct the user to connect
the electrodes (pads) to the patient. Once the pads are
attached, everyone should avoid touching the patient so
as to avoid false readings by the unit. The pads allow the
AED to examine the electrical output from the heart and
determine if the patient is in a shockable rhythm (either
ventricular fibrillation or ventricular tachycardia). If
the device determines that a shock is warranted, it will
use the battery to charge its internal capacitor in preparation
to deliver the shock. This system is not only safer (charging
only when required), but also allows for a faster delivery
of the electrical current.
charged, the device instructs the user to ensure no one
is touching the patient and then to press a button to deliver
the shock; human intervention is usually required to deliver
the shock to the patient in order to avoid the possibility
of accidental injury to another person (which can result
from a responder or bystander touching the patient at the
time of the shock). Depending on the manufacturer and particular
model, after the shock is delivered most devices will analyze
the patient and either instruct CPR to be given, or administer
AED units have an 'event memory' which store the ECG of
the patient along with details of the time the unit was
activated and the number and strength of any shocks delivered.
Some units also have voice recording abilities[citation
needed] to monitor the actions taken
by the personnel in order to ascertain if these had any
impact on the survival outcome. All this recorded data can
be either downloaded to a computer or printed out so that
the providing organisation or responsible body is able to
see the effectiveness of both CPR and defibrillation. Some
AED units even provide feedback on the quality of the compressions
provided by the rescuer.
first commercially available AEDs were all of a monophasic
type, which gave a high-energy shock, up to 360 to 400 joules
depending on the model. This caused increased cardiac injury
and in some cases second and third-degree burns around the
shock pad sites. Newer AEDs (manufactured after late 2003)
have tended to utilise biphasic algorithms which give two
sequential lower-energy shocks of 120 - 200 joules, with
each shock moving in an opposite polarity between the pads.
This lower-energy waveform has proven more effective in
clinical tests, as well as offering a reduced rate of complications
and reduced recovery time.
placement of pads on chest
an automated external defibrillator requires minimal training
to use. It automatically diagnoses the heart rhythm and
determines if a shock is needed. Automatic models will administer
the shock without the user's command. Semi-automatic models
will tell the user that a shock is needed, but the user
must tell the machine to do so, usually by pressing a button.
In most circumstances, the user cannot override a "no shock"
advisory by an AED. Some AEDs may be used on children -
those under 55 lbs (25 kg) in weight or under
age 8. If a particular model of AED is approved for pediatric
use, all that is required is the use of more appropriate
AEDs approved for use in the United
States use an electronic voice to prompt users through
each step. Because the user of an AED may be hearing
impaired, many AEDs now include visual prompts as well.
Most units are designed for use by non-medical operators.
Their ease of use has given rise to the notion of public
access defibrillation (PAD), which experts agree has the
potential to be the single greatest advance in the treatment
of out-of-hospital cardiac arrest since the invention of
number of people who survive sudden cardiac arrest is increasing
gradually, thanks to the use of AEDs. For this reason, the
Sudden Cardiac Arrest Foundation developed the National
SCA Survivor Network, which provides a platform for
mutual support and for engaging in the mission to help save
external defibrillators are now easy enough to use that
most states in the United States include the "good faith"
use of an AED by any person under Good
"Good faith" protection under a Good Samaritan law means
that a volunteer responder (not acting as a part of one's
occupation) cannot be held civilly liable for the harm or
death of a victim by providing improper or inadequate care,
given that the harm or death was not intentional and the
responder was acting within the limits of their training
and in good faith. In the United States, Good Samaritan
laws provide some protection for the use of AEDs by trained
and untrained responders.
AEDs create little liability if used correctly;
NREMT-B and many state Emergency
Medical Technician (EMT) training and many CPR classes
incorporate or offer AED education as a part of their program.
In addition to Good Samaritan laws, Ontario, Canada also
has the "Chase
McEachern Act (Heart Defibrillator Civil Liability),
2007 (Bill 171 – Subsection N)", passed in June, 2007,
which protects individuals from liability for damages that
may occur from their use of an AED to save someone's life
at the immediate scene of an emergency unless damages are
caused by gross negligence.
external defibrillators are under recent scrutiny by the
and Drug Administration (FDA) which is now considering
reclassifying AEDs as class III premarket
approval devices. The major reason for this appears
to be technical malfunctions, which likely contributed to
more than 750 deaths in the 5 year period between 2004 and
2009, in most cases by component failures or design errors.
During the same period, up to 70 types of AEDs have been
recalled, including recalls from every AED manufacturer
in the world.