Automated External Defibrillation

Updated: May 05, 2022
  • Author: Joseph J Bocka, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Kouwenhouven showed that electrical shocks applied to dogs within 30 seconds of an induced ventricular fibrillation (VF) could produce a 98% rate of resuscitation; however, those shocked after 2 minutes of ventricular fibrillation had only a 27% resuscitation rate. [1] This gave rise to the goal of early defibrillation for ventricular fibrillation and pulseless ventricular tachycardia (VT). The use of automated external defibrillators (AEDs) can aid in reaching this objective.

Survival rates for individuals with ventricular fibrillation treated by AEDs have been reported between 0% and 31%. Comparatively, the survival rates for performing basic cardiopulmonary resuscitation (CPR) alone are reported between 0% and 6%. Theoretically, even more lives could be saved if targeted members of the general public could obtain early access to and have training in the use of AEDs and CPR. Unfortunately, only about 10-15% of cardiac arrests occur in a public place and even fewer are witnessed. [2]

For patient education information, see Automated External Defibrillators (AED) and Cardiopulmonary Resuscitation (CPR).




In 1775, Abildgaard described a series of experiments in which he made hens lifeless with electrical impulses applied through the body. He could not restore a pulse, however, unless shocks were delivered across the chest. In 1849, Ludwig and Hoffa first described what Abildgaard had induced. They originated and defined the term fibrillation of the ventricles. In 1900, Prevost and Batelli conducted research on ventricular fibrillation (VF) in dogs. They found that weak alternating current (AC) or direct current (DC) shocks produced ventricular fibrillation, while much stronger current was needed to defibrillate. [3]

Wiggers and Wegria expanded on the work of Prevost and Battelli, describing a vulnerable period of the cardiac cycle utilized to induce ventricular fibrillation. They also reported that the current delivered was the key to successfully performing what they termed "countershocking" of ventricular fibrillation. [3]


Development of practical defibrillators began in the 1920s with funding from Consolidated Edison of New York in response to an increasing number of electric shock accidents and deaths. In 1947, Beck et al performed the first successful human defibrillation using specially designed internal cardiac paddles. [4] He used two 110-volt, 1.5-amp AC current shocks to resuscitate a 14-year-old boy who had become pulseless during elective chest surgery. In 1956, Zoll et al performed the first successful human external defibrillation using a 15-amp AC current that produced 710 volts applied across the chest for 0.15 seconds. [5] In 1961, Alexander, Kleiger, and Lown first described the use of AC current for terminating ventricular tachycardia (VT). [6] Work by Lown et al in the early 1960s demonstrated the superiority and safety of DC over AC for defibrillation. [3]

Ambulance-transported Belfast physicians first performed successful prehospital defibrillation in 1966. [3] Defibrillation by emergency medical technicians (EMTs) without the presence of physicians was first performed in Portland, Oregon, in 1969 and was reported in 1972. [7]

Automatic defibrillators

In the early 1970s, Dr Arch Diack, Dr W. Stanley Welborn, and Robert Rullman developed several prototype AEDs that were tested in the Portland area. [8] They later formed the Cardiac Resuscitator Corporation to market their device.

Prehospital trials began in Brighton, England, in 1980 using the Heart Aid. The device weighed 28 pounds and used an oral/epigastric and a precordial electrode to record ECG tracings and deliver electrical shocks. It was also capable of transcutaneously pacing the heart. [9] In 1982, the US Food and Drug Administration (FDA) gave approval for EMT-defibrillation (EMT-D) clinical trials. Early US investigations of manual EMT-D were carried out in Washington, Iowa, Minnesota, and Tennessee.

In the early 1990s, successful training and use of AEDs by police officers and other first responders was reported. AED use by lay personnel was approved by the FDA in the 1990s, and Good Samaritan legislation soon followed.


Machine Mechanics

Early models of AEDs required inserting an oral/epigastric electrode and placing a second electrode on the chest. Current AEDs require the placement of pads at the right sternal border and at the cardiac apex, or the anterior and posterior upper torso in infants and small children. These electrodes serve to both monitor and defibrillate. AEDs also can inform the user when lead contact is poor, when the machine is preparing to defibrillate, when to check for a pulse, when a nonshockable rhythm is present, or when motion is detected.

Rhythm analysis

Early AEDs were designed to respond primarily to a heart rate greater than 150 electrical complexes per minute and an electrocardiographic wave (QRS) amplitude greater than 0.15 mm. Presently, the ECG rhythm is analyzed via a combination of several methods. In addition to rate and amplitude criteria, the QRS is analyzed as to its slope, morphology, power spectrum density, and time away from the isoelectric baseline for preset levels defined as abnormal. Checks are made in 2- to 4-second intervals. In general, if abnormal complexes are detected for more than double the frequency of any other QRS for three consecutive checks, the AED will be primed to deliver a shock.

Fine ventricular fibrillation (VF) presents the greatest detection challenge. A trade-off exists between setting the amplitude criterion low enough to detect fine fibrillation, yet high enough to avoid shocking asystole or artifact. The sensitivity of detecting VF by AEDs has been reported as 76-96%. Specificity (correctly identifying non-VF rhythms) is reported to be nearly 100%.

Biphasic versus monophasic

Monophasic defibrillation delivers a charge in only one direction. Biphasic defibrillation delivers a charge in one direction for half of the shock and in the electrically opposite direction for the second half.

Dog studies have shown less conduction block and fewer ST segment changes after biphasic shock delivery than after monophasic delivery. Human studies have shown monophasic delivery to be equivalent to biphasic shocks for electrophysiologic study-induced (EPS-induced) and prehospital VF and ventricular tachycardia (VT). [10] Also, studies have shown that a biphasic waveform of 115 J is equivalent to a monophasic wave of about 200 J. Because of the decreased energy needed, most internal cardioversion defibrillators now use biphasic waveforms. Most manufacturers are converting to biphasic AEDs, as the lower amount of energy used can result in both longer battery life and a shorter time to full charge.

While there may be a theoretical clinical advantage to using biphasic defibrillation, most patient studies and reports have shown equivalency and not superiority of one form when using equivalent dosages (biphasic dosages are lower). [11, 12, 13]


Studies with implantable defibrillators have shown a difference in outcome related to electrode polarity. The only prospective study with AEDs, which was performed by Weaver in 1993, showed no difference in survival related to polarity while using a monophasic unit. [14]


Classic AED Studies


Classic AED studies have investigated the efficacy of AEDs in urban, suburban, and rural locations.


In 1987, Cummins et al reported a controlled study comparing the effectiveness of AEDs versus manual defibrillators used by EMTs to treat 147 patients in ventricular fibrillation (VF) in suburban Seattle, Washington. No statistically significant differences in rates of admission (54% AED; 50% manual) or survival to discharge (30% AED; 23% manual) were noted. [15]

In 1988, Weaver et al reported the results of AED use by non-EMT first responders (3.3-min response time) compared with basic CPR by first responders (3.4-min response) followed by AED use by paramedics (5.1-min response). A prototype AED was used and modified halfway through the study. The combined results in 504 patients in VF showed no significant difference in admission rates (59% first responder AED; 53% paramedic AED) but a higher rate of survival to discharge in the first responder AED group (30% versus 19%). [16]


In 1986, Stults et al reported on a study in a rural setting that compared AEDs with manual defibrillators, as used by EMTs. The results of 88 patients in VF showed no significant difference in rates of admission (29% AED; 32% manual) or survival to discharge (17% AED; 13% manual). [17]


Bachman et al failed to confirm the results from Iowa and Seattle in rural northeast Minnesota. [18] They reported survival to discharge rates of 11% for paramedics, 5% for EMTs with manual defibrillators, and 2.5% for cardiac arrests handled by EMTs performing CPR. Separate analysis for VF was not performed. They found no unwitnessed arrest survivors as earlier studies had, and results caused them to question the use of AEDs in rural areas.

In contrast, Vukov studied EMT defibrillation in rural southeast Minnesota in 1988. [19] In a report of 63 patients, patients treated by EMTs with AEDs had significantly greater admission rates (30% versus 12%) and survival to discharge rates (17% versus 4%) than patients treated by EMTs without AEDs.

Detroit, Chicago, and New York 

In data that have been presented but not published, basic EMTs with AEDs treated 595 patients who were in cardiac arrest in Detroit. Only about 20% were found in VF. About 5% were admitted, and none survived to discharge. Possible factors contributing to the low initial VF and survival rates were an EMS response time of more than 10 minutes and an estimated 5-10 minute time from collapse until EMS was summoned.

Similar studies reported a 4% survival rate from VF in Chicago and a 5% survival rate in New York. Average response times were greater than 10-12 minutes.


Stults and Brown looked at the question of EMTs handling defibrillation without paramedic backup. [20] Of the 271 patients with VF who were shocked, 111 patients who initially converted to organized rhythms after defibrillation were analyzed. Of these, 19 (17%) refibrillated and 11 were reconverted by the defibrillation-trained EMTs. Among the 111 patients who initially converted, admission rates were lower (53% versus 76%) but not statistically significantly lower (P > 0.05) for those who refibrillated. Survival to discharge rates were similar (37% refibrillation versus 35% nonrefibrillation).

Time to defibrillation

Early Seattle studies found a significant difference in time to defibrillation: 1.1 minutes for AEDs versus 2 minutes for manual defibrillators. Bocka found that EMTs using fully automated defibrillators in the field were on average 30 seconds faster than counterparts using semiautomated devices. [21]


AED Precautions

Patients must be medically unstable or pulseless before AEDs are used. They should be pulseless before assessing the rhythm. This becomes increasingly important as more laypersons are given the opportunity to use AEDs. 

Most states have passed a liability waiver for bystanders who use an AED to assist an unconscious patient. The principal risk is that another person may be touching the patient when the shock is administered. Shocking of bystanders may also occur if the patient is lying in a pool of liquid.

To prevent inaccurate analysis, CPR should be halted while the unit is analyzing the rhythm. Most new units have a motion or CPR detector.

The AED should be used only with caution in a moving vehicle. [22] If being used on a patient in transport, frequent stops for pulse and AED monitoring checks should be made. Most units are designed to warn when motion or poor contact is detected.

As with manual defibrillation, the chest does not need to be shaved prior to electrode placement but, if wet, it should be dried off. Water spots or nicks in the skin result in areas of decreased resistance and could lead to local burns as well as uneven and ineffective defibrillation. Look for nitroglycerin patches and remove them to prevent possible explosive risk.

Proper maintenance is important. However, it is estimated that less than 10% of AED users maintain their AED or replace the batteries according to the manufacturer's recommendations.

Repeated "check electrode" warnings when electrodes seem properly placed may be from fractured electrodes. Replace them and retry.

Caution should be used when applying AEDs in the presence of electromagnetic interference (EMI). One study showed a 2% false-positive rate, with shocks advised for sinus rhythm and 3.5% sensing motion artifact in the presence of EMI. [23]

Each AED should be programmed to the most current American Heart Association Defibrillation Guidelines. This should be checked, especially when purchasing an older or used AED. Arrangements should be made for reprogramming whenever changes are announced.

Several AED units have been recalled for various problems. The FDA posts summaries of information about the most serious recalls of medical devices, such as AEDs, on its List of Device Recalls Web page.

Concern has been raised about the safety of providers and AED assessment during CPR. However, a study Edelson et al concludes that continuing chest compression while the AED is charging is an underused technique in clinical practice, as it is associated with decreased hands-off time preceding defibrillation, with minimal risk to patients or rescuers. [24]


AED Selection Factors

Population density : Stapczynski et al concluded that areas with a population density of fewer than 100 persons per square mile received little benefit from AEDs. [25] A study from Washington identified 172 sites of higher incidence (of 71,000 sites). Similar local assessments may aid in efficient public AED location.

It is becoming increasingly common for AEDs to be placed in locations with significant public traffic or density (see Public Access Defibrillation below), such as stadiums and other event venues and airports. American Airlines was the first airline to carry AEDs on aircraft during long overwater flights in 1997, and subsequent FAA regulations mandated aircraft to carry AEDs and for flight personnel to be trained in their use (amendment to part 121 of Aviation Medical Assistance Act of 1998).

Response time: On average, response time should be less than 4-6 minutes for the patient to benefit from the use of an AED.

Tiers: Tiered response systems should have compatible equipment. If an AED is to be used by a first responder, defibrillators or their electrode wiring system should be compatible with the transporting units that follow.

Monitor: If the unit also is used by paramedics for monitoring and not just by AED technicians for cardiac arrest, a monitor screen is needed. Printout capabilities are also desirable.

Event recording: A paper recording of the event may be sufficient for medical control; however, the need for a full set of data should influence equipment choice, since the data need to be downloaded. Because most of the data downloaded by AED units are not interchangeable, a setting in which data from various agencies needs to be collected and combined must use similar AEDs that can communicate; if they do not have this capability, data must be collected by hand.

Good Samaritan Immunity and Local Requirements : While most states provide excellent liability immunity for proper use and have minimal requirements for placement, one should check local laws before placement. State requirements can be found at the National Conference of State Legislatures page.


Public Access Defibrillation

Public access defibrillation (PAD) has been shown to be an important part of successful chain of survival programs. [26, 27] Placement of AEDs has been most cost effective in select locations, including casinos, airports, stadiums, health clubs, universities, and senior centers. [28]   [29, 30, 31]

In the 1990s, AED use by lay personnel was approved by the FDA, and Good Samaritan legislation soon followed. AED training was included in the American Red Cross basic CPR course beginning in March of 1999. In November 2002, the Phillips HeartStart AED was approved for home use with a prescription. New York State became the first state to mandate AEDs in schools in May 2003. The FAA mandated in April 2004 that all large passenger-carrying US airlines carry and have personnel trained in the use of AEDs.

In September 2004, the FDA began to allow home AED sales without a prescription. However, routine AED use in high-risk homes is controversial. On the other hand, its use in high-risk populated areas has resulted in numerous lives saved in casinos, schools, stadiums, and airports. In 2014, the California Supreme Court, in the case of Verdugo vs The Target Corporation (S207313), ruled unanimously that California law does not require retailers to have defibrillators available for medical emergencies. [32]

A systematic review of AED accessibility and the survival rate in out-of-hospital cardiac arrest, which included 16 studies with 55,537 participants, found that one-month survival rate was 39.3% in schools, sports venues, and airports compared with 23.5% in other sites. one-month survival rate was 39.3% in schools, sports venues and airports compared with 23.5% in other sites. Longer time between cardiac arrest and AED arrival, and greater distance between the location of the AEDs and the location of the cardiac arrest, were negatively correlated with one-month survival rates, but the correlations were not statistically significant. [33]

The use of autonomous flight AED-equipped drones has been proposed as a means of quickly delivering AEDs to bystanders over a large region. In such systems, drones would be housed in drone docking stations for dispatch. [34, 35, 36]  In a test of concept, drones were flown a median flight distance of 3.2 km to simulated out-of-hospital cardiac arrests, and response times were compared with those of actual out-of-hospital cardiac arrests that had occurred in the same location. The median time from dispatch to arrival of the drone was 5:21 minutes, versus a median time of 22:00 minutes for arrival of emergency medical services. [37]

A pilot study in Sweden, in which three AED-equipped drones were used to cover a 125 square kilometer–region with approximately 80,000 inhabitants, demonstrated that AEDs can be carried by drones to real-life cases of out-of-hospital cardiac arrest with a successful AED delivery rate of 92%. [38]  Another pilot study of drone-delivered AEDs is currently in progress in Ontario, Canada. A study by Sedig et al of the community in the study area found that the concept was acceptable, but successful uptake in smaller communities would require attention to a community’s understanding of cardiac arrest, CPR, and AED use. [39]



AED Manufacturers and Devices

AED manufacturers include the following:

FDA-approved AEDs are listed in the table below. [40]

Table. Automated External Defibrillators Approved by the US Food and Drug Administration (Open Table in a new window)


Device Name

Approval Date

Cardiac Science Corporation

Powerheart G3 AED


Powerheart G3 Plus AED


Powerheart G5 AED


Powerheart G3 PRO AED


Defibtech, LLC

Lifeline/ReviveR DDU-100


Lifeline/ReviveR AUTO DDU-120


Lifeline/ReviveR VIEW DDU-2300


Lifeline/ReviveR VIEW AUTO DDU-2200


Lifeline/ReviveR ECG DDU-2450


Lifeline/ReviveR ECG+ DDU-2475


HeartSine Technologies, LLC

SAM 350P (Samaritan Public Access Automated External Defibrillator)


SAM 360P


SAM 450P


Philips Medical Systems

HeartStart Home


HeartStart OnSite


HeartStart FR3


Physio-Control, Inc.

LIFEPAK CR Plus Defibrillator




LIFEPAK CR2 Defibrillator


LIFEPAK 15 Monitor/Defibrillator


LIFEPAK 20E Defibrillator/ Monitor


LIFEPAK 1000 Defibrillator


ZOLL Medical Corporation  

AED Plus and Fully Automatic AED Plus         


X Series Defibrillator


R Series Defibrillator


AED Pro Defibrillator


AED 3 BLS Defibrillator


Propaq MD Defibrillator


AED 3 Defibrillator



The FDA and AEDs

The FDA's Requirement for Premarket Approval for Automated External Defibrillator System, which became effective in 2015, requires manufacturers of AEDs and necessary accessories to submit premarket approval (PMA) applications that focus specifically on the critical requirements necessary to ensure AEDs are safe and reliable. The filing of PMA applications for AED accessories necessary for the AED to detect and interpret an electrocardiogram and deliver an electrical shock (eg, pad electrodes, batteries, adapters, and hardware keys for pediatric use) was extended from February 3, 2020 to February 3, 2022. [41]