An automated external defibrillator (AED) is a portable, battery-operated medical device that automatically diagnoses life-threatening cardiac arrhythmias, such as ventricular fibrillation or pulseless ventricular tachycardia, in victims of sudden cardiac arrest and delivers an electrical shock through adhesive pads placed on the chest to restore normal heart rhythm.[1] These devices are designed for use by laypersons as well as trained personnel, featuring voice prompts, visual instructions, and built-in safeguards to prevent inappropriate shocks.[2]The development of AEDs builds on early advancements in defibrillation technology, which originated in the late 19th century with animal experiments demonstrating the potential of electrical shocks to restore heart function.[3] In 1947, American surgeon Claude Beck performed the first successful human defibrillation using an internal device during open-heart surgery, followed by the invention of the first external defibrillator in 1956 by Paul Zoll.[3] A pivotal milestone came in 1957 when William Kouwenhoven and his team at Johns Hopkins University introduced the first portable external defibrillator, enabling closed-chest applications without surgery.[3] The automation critical to modern AEDs emerged in the 1970s through work by researchers like Arch Diack, W. Stanley Welborn, and Henry Rullman, who developed the Heart-Aid, the first commercial AED, in 1979.[4] By the 1990s, regulatory approvals and public access programs, supported by organizations like the American Heart Association, led to widespread deployment in public spaces, schools, and workplaces.[4]AEDs function by adhering self-adhesive electrode pads to the bare chest of an unresponsive, non-breathing victim, after which the device automatically assesses the heart rhythm via electrocardiogram signals.[2] If a shockable rhythm is detected, the AED charges its capacitor and instructs the user to press a button to deliver the shock, typically between 150 and 300 joules, while advising against touching the patient during analysis or delivery to ensure safety.[1] Post-shock, the device reanalyzes the rhythm and may prompt additional shocks or CPR, with some models capable of up to three sequential deliveries before further intervention.[4]Maintenance is minimal, involving periodic battery and pad replacement, and all AEDs sold in the United States are regulated by the Food and Drug Administration as Class III medical devices requiring premarket approval for safety and efficacy.[1]The deployment of AEDs has dramatically improved survival outcomes for out-of-hospital sudden cardiac arrest, which claims approximately 350,000 lives annually in the United States and affects people of all ages without warning.[2] Without immediate intervention, survival rates drop by 7% to 10% per minute, but prompt use of an AED within the first three to five minutes, combined with CPR, can boost survival to 50% to 74%.[2][5] Studies show that communities with public access AED programs experience nearly doubled survival rates compared to those without, underscoring their role in bridging the gap until professional emergency services arrive.[6] Ongoing efforts focus on increasing AED accessibility, training, and integration with emergency response systems to further enhance these life-saving impacts.[7]
Definition and Overview
What is an AED
An automated external defibrillator (AED) is a portable electronic device designed to diagnose life-threatening cardiac arrhythmias, such as ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT), and deliver an electric shock to the heart to restore a normal rhythm.[8][1] The device automatically analyzes the patient's electrocardiogram (ECG) to detect shockable rhythms and advises the user on whether a shock is needed, making it suitable for use by bystanders with minimal training.[9][10]AEDs play a critical role in the treatment of sudden cardiac arrest (SCA), a condition where the heart abruptly stops beating effectively, often due to VF or VT, leading to immediate loss of consciousness and pulse.[11] As part of the chain of survival—a sequence of interventions including early recognition, CPR, defibrillation, advanced care, and recovery—prompt AED use can significantly improve survival rates by restoring a perfusing rhythm before professional help arrives.[11][12]Unlike manual defibrillators, which require trained healthcare professionals to interpret ECG rhythms, select energy levels, and deliver shocks, AEDs are fully automated for non-expert use, incorporating built-in ECG analysis algorithms and voice prompts to guide rescuers through the process.[10][13] This design enhances accessibility in public settings, reducing response time and errors.[9]Physically, an AED is battery-powered, lightweight (typically 1.5 to 3 kg), and compact for easy portability, featuring self-adhesive electrode pads that are applied to the patient's chest to monitor ECG and deliver the shock.[14][15][13]
Types of AEDs
Automated external defibrillators (AEDs) are primarily classified by their level of automation, which determines the degree of user involvement in shock delivery. Fully automatic AEDs perform rhythm analysis and, if a shockable arrhythmia is detected, deliver the electrical shock without requiring the rescuer to press a button, minimizing hesitation in high-stress situations.[1] In contrast, semi-automatic AEDs analyze the heart rhythm and provide an audible or visual advisory recommending a shock, but the user must manually initiate delivery by pressing a designated button after pad placement.[1] This distinction enhances usability for lay rescuers in fully automatic models, while semi-automatic versions offer an additional safety check preferred in some professional settings.[16]AEDs are also categorized by intended use environment, leading to differences in design for professional versus public-access applications. Professional-use AEDs, typically deployed in hospitals or clinical settings, incorporate advanced features such as manual override capabilities, higher energy options, and integration with monitoring equipment for trained healthcare providers.[17] Public-access AEDs, designed for untrained bystanders in locations like airports and schools, emphasize simplicity with voice prompts, self-testing, and rugged casings to withstand environmental exposure, often including pediatric dose attenuation for child victims.[1] These models may integrate CPR feedback mechanisms, such as metronomes or compression sensors, to guide rescuers through basic life support protocols.[18]Certain public-access AEDs, such as the ZOLL AED Plus, can be suitable for home use due to their portability, long battery life (up to 5 years), and compact storage, allowing family members in high-risk households to respond to cardiac events.[19]As of 2025, IoT-connected AEDs represent an emerging variant focused on enhancing deployment efficiency through real-time connectivity. These devices incorporate GPS or Wi-Fi modules for location tracking, allowing centralized systems to monitor cabinet status, battery levels, and usage, thereby alerting authorities to maintenance needs or guiding rescuers via mobile apps in emergencies.[20]
Medical Indications
Cardiac Conditions Treated
Automated external defibrillators (AEDs) are primarily indicated for the treatment of two life-threatening cardiac arrhythmias: ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). In VF, the heart's electrical activity becomes chaotic and uncoordinated, resulting in quivering of the ventricles that prevents effective blood pumping and leads to immediate cardiac arrest.[10] Similarly, pulseless VT involves a rapid, abnormal ventricular rhythm that fails to generate a palpable pulse, compromising cardiac output and requiring urgent intervention to restore organized electrical activity.[4] These shockable rhythms are the core targets for AED use in out-of-hospital and in-hospital settings, as early defibrillation can interrupt the arrhythmia and potentially restore a perfusing rhythm.[21]AEDs incorporate advanced algorithms to analyze the cardiac rhythm and exclude non-shockable conditions, such as asystole and pulseless electrical activity (PEA), where defibrillation would be ineffective or harmful. Asystole represents a flatline absence of electrical activity, while PEA features organized electrical impulses without mechanical ventricular contraction, both of which do not respond to electrical shocks and instead necessitate CPR and pharmacological management.[22][23] The device's rhythm detection software prompts the user to withhold shocking in these cases, ensuring appropriate application only to VF or pulseless VT.[24]The physiological basis for AED defibrillation lies in delivering a high-energy electrical current that simultaneously depolarizes a critical mass of the myocardium, extinguishing multiple reentrant wavelets in VF or pulseless VT and creating a temporary electrical quiescence. This depolarization allows the sinoatrial node to regain dominance and reestablish a normal sinus rhythm, thereby restoring coordinated cardiac contraction.[10][25] Modern AEDs predominantly employ biphasic truncated exponential waveforms, which reverse the current direction mid-shock to enhance efficacy at lower energy levels—typically 150-200 joules—compared to older monophasic waveforms that require higher energies up to 360 joules.[26][27] Biphasic shocks achieve superior defibrillation success rates by more effectively depolarizing myocardial tissue with reduced risk of post-shock damage.[28]
Impact of Delayed Defibrillation
Sudden cardiac arrest (SCA), often presenting as ventricular fibrillation (VF) or ventricular tachycardia (VT), requires immediate intervention to restore normal heart rhythm and prevent irreversible damage. The chain of survival model, established by the American Heart Association (AHA), emphasizes early defibrillation as a critical link in improving outcomes for out-of-hospital cardiac arrest (OHCA). Without prompt defibrillation, survival rates decline rapidly; specifically, for witnessed VF arrests, each minute without CPR results in a 7-10% decrease in survival probability.[29] When bystander CPR is initiated, this decline is mitigated to approximately 3-4% per minute until defibrillation occurs, highlighting the time-sensitive nature of SCA management.[29]Delays in defibrillation not only reduce overall survival but also heighten the risk of neurological injury due to cerebral hypoxia. Brain cells begin to suffer irreversible damage after 4-6 minutes without adequate oxygenation from CPR or defibrillation, leading to potential long-term cognitive impairments or coma in survivors.[30] Studies on OHCA demonstrate this urgency: survival to hospital discharge can approach 50% to 70% when defibrillation occurs within 3 to 5 minutes of collapse, but plummets to less than 10% after 10 minutes.[31] These outcomes underscore the exponential deterioration in prognosis as time elapses, with early rhythm restoration being pivotal for both survival and functional recovery.[32]Bystander intervention plays a vital role in bridging these critical delays by initiating CPR and locating an automated external defibrillator (AED), thereby extending the window for effective treatment. AHA data indicate that bystander CPR alone can double or triple short-term survival rates in OHCA compared to no intervention, while combining it with AED use further enhances neurological outcomes by preserving brain function during the pre-arrival period.[33] Public access to AEDs, supported by bystander action, has been shown to achieve median survival rates of around 40% in treated OHCA cases, emphasizing the community-level impact of rapid response.[34]
User Prerequisites
Automated external defibrillators (AEDs) are intentionally designed for use by laypersons without prior medical training, enabling untrained bystanders to intervene effectively during sudden cardiac arrest through clear audio and visual prompts that guide the entire process.[35] This accessibility is a core feature of public access defibrillation programs, allowing immediate action in emergencies where professional help may be delayed.[36]The fundamental prerequisites for safe AED operation include the ability to assess a victim's responsiveness by tapping and shouting, call emergency services, and follow the device's step-by-step instructions, which may also involve initiating basic CPR if the AED advises continued compressions. No advanced skills are required beyond these basics, as the AED analyzes the heart rhythm automatically and only delivers a shock if necessary, minimizing the risk of user error.[35]While not mandatory, formal training is highly recommended to build confidence and proficiency, with organizations like the American Heart Association (AHA) and American Red Cross offering CPR/AED courses typically lasting 2-4 hours that include hands-on practice with manikins and AED trainers.[37][38] These programs emphasize recognition of cardiac arrest and integration of AED use with CPR, and annual refreshers are advised to maintain skills.[35]Special considerations apply for pediatric and pregnant patients to ensure appropriate energy delivery. For children under 8 years or weighing less than 25 kg, a dose attenuator or pediatric pads should be used to reduce shock energy, as standard adult pads may deliver excessive voltage. In pregnant individuals beyond 20 weeks gestation, AED use remains safe and unmodified, with rescuers performing manual left uterine displacement during CPR to optimize circulation, prioritizing maternal resuscitation to benefit both mother and fetus.[39]
Design and Operation
Core Components
The core components of an automated external defibrillator (AED) encompass both hardware and software elements designed for reliability, ease of use, and effective cardiac rhythmanalysis and shock delivery. The hardware includes disposable, self-adhesive electrodes equipped with conductive gel to ensure optimal skin contact and electrical conduction during use.[40] These pads are typically pre-gelled and single-use to prevent contamination and maintain efficacy, adhering firmly to the patient's chest for rapid application.[41] The power source is a non-rechargeable lithium battery, often lithium manganese dioxide, with a standby life of 3 to 5 years, enabling multiple shocks or extended monitoring without frequent replacement.[42] The device's outer casing is constructed from durable, rugged materials that provide water resistance, commonly achieving an IP55 rating for protection against dust and water jets, ensuring functionality in various environmental conditions.[43]On the software side, a microprocessor serves as the central processing unit, employing specialized algorithms to analyze electrocardiogram (ECG) signals from the electrodes. These algorithms, such as amplitude-based or probability-based detection methods, evaluate rhythm characteristics like QRS complex amplitude, frequency, and slope to distinguish shockable arrhythmias (e.g., ventricular fibrillation) from non-shockable ones.[4] The analysis occurs automatically upon electrode attachment, with the microprocessor processing data in seconds to advise on shock necessity.[44]User interface components often include a display screen, such as an LCD, that shows device status, such as battery level, pad integrity, and readiness indicators in models equipped with one, allowing quick visual confirmation without activation.[45] Complementing this is an audio system delivering clear voice prompts that guide the user through each step, available in multiple languages to accommodate diverse operators.[46]For energy delivery, a high-voltage capacitor stores the charge from the battery, rapidly discharging it to generate the defibrillationpulse. Modern AEDs utilize a biphasic truncated exponentialwaveform, where current flows in two phases of opposite polarity to enhance defibrillation efficacy at lower energies (typically 150-360 J) while minimizing myocardial damage.[47] This waveform is produced by truncating the exponential decay from the capacitor, often using configurations like 100-200 μF capacitance for optimal performance.[48]
Operational Mechanism
The operational mechanism of an automated external defibrillator (AED) begins with rhythm analysis, where the device employs algorithms to evaluate the patient's electrocardiogram (ECG) signal for shockable rhythms such as ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). These algorithms first filter out noise and artifacts from the ECG, including those caused by patient movement, loose electrodes, or environmental interference, using techniques like digital signal processing to isolate relevant cardiac waveforms.[49] The core of the analysis focuses on detecting QRS complexes—the prominent deflections in the ECG representing ventricular depolarization—and assessing their morphology, rate, and organization to distinguish shockable from non-shockable rhythms. Modern AED algorithms achieve high performance, with sensitivity exceeding 95% for detecting VF and VT, ensuring minimal missed opportunities for intervention, and specificity greater than 99% for identifying non-shockable rhythms like asystole or pulseless electrical activity, thereby avoiding unnecessary shocks.[50][51]Upon detecting a shockable rhythm, the AED initiates the charge and shock sequence by activating its internal capacitor to build electrical energy, typically delivering a biphasic truncated exponentialwaveform at 120-200 joules, which is effective across a range of patient thoracic impedances. This biphasic waveform reverses direction midway through delivery, enhancing defibrillation efficacy while reducing the required energy compared to monophasic shocks. The device incorporates impedance compensation, measuring transthoracic impedance via the electrodes and dynamically adjusting the shock duration or voltage to maintain consistent current delivery, accommodating variations due to patient size, chest wall thickness, or electrode contact.[10][52] If the rhythm is shockable, the AED provides voice or visual prompts to ensure the rescuer stands clear before the shock is delivered, either automatically (in fully automatic models) or upon pressing the button (in semi-automatic models), after confirmation.[53]Following shock delivery, the AED's post-shock protocol immediately prompts the rescuer to resume cardiopulmonary resuscitation (CPR), emphasizing chest compressions to restore circulation without pausing for rhythm checks. This aligns with evidence-based guidelines recommending uninterrupted CPR for approximately two minutes—equivalent to about five cycles of 30:2 compressions and ventilations—before the device automatically pauses to re-analyze the rhythm. The re-analysis repeats the initial detection process, potentially advising additional shocks if a shockable rhythm persists, while minimizing interruptions to CPR to optimize outcomes.[4][54]Safety interlocks are integral to the AED's mechanism, preventing inadvertent or inappropriate shock delivery to enhance user and patient safety. These include software safeguards that withhold shocks for non-shockable rhythms, relying on the high specificity of the analysis algorithm to avoid delivering energy when it could cause harm, such as in organized rhythms or asystole. Additionally, motion detection sensors monitor for excessive patient or rescuer movement, such as during ongoing CPR, and issue voice prompts to "stop motion" while suspending analysis until stability is achieved, thereby reducing false positives from artifacts.[8][55] Physical interlocks, like requiring electrode attachment and proper pad placement, further ensure shocks only occur under controlled conditions.[56]
Step-by-Step Usage Procedure
The use of an automated external defibrillator (AED) begins with ensuring the safety of the rescuer and the victim. First, assess the scene for any hazards that could endanger responders or bystanders. Next, check the victim for responsiveness by tapping their shoulder and shouting; if unresponsive, simultaneously shout for help and activate the emergency response system by calling 911 or the local emergency number to request professional medical assistance. If another person is available, instruct them to retrieve the AED while you begin cardiopulmonary resuscitation (CPR) if the victim is not breathing normally.[54]Once the AED arrives, power it on by pressing the power button or opening the lid, as some models activate automatically; the device will provide voice prompts to guide the user through the process. Expose the victim's chest by removing or cutting away clothing to ensure bare, dry skin for optimal pad adhesion—wipe the chest dry if wet, but do not delay treatment. Apply the self-adhesive electrode pads in the anterior-lateral position: place one pad on the upper right chest below the right collarbone and the other on the lower left side of the chest, below the armpit and to the left of the nipple. Avoid placing pads directly over jewelry, medication patches, or implanted devices such as pacemakers, as this can interfere with shock delivery; instead, position pads at least one inch away from such devices and remove any metal objects like necklaces.[54][2][57]With pads securely attached, follow the AED's prompts to initiate rhythm analysis; ensure no one touches the victim during this hands-off period, as the device detects shockable rhythms such as ventricular fibrillation or pulseless ventricular tachycardia. If the AED advises a shock, confirm that everyone is clear of the victim by loudly stating "Clear!" and visually verifying, then, for semi-automatic models, press the shock button; fully automatic models will deliver the shock automatically once the area is clear. Immediately after the shock, or if no shock is advised, resume CPR starting with chest compressions.[54][2]Integrate AED use with CPR by performing high-quality compressions at a rate of 100–120 per minute and depth of about 2 inches, allowing full chest recoil, in cycles of 30 compressions to 2 breaths for about 2 minutes. After each 2-minute CPR cycle, stand clear and allow the AED to reanalyze the rhythm, repeating the shock and CPR sequence as prompted. Continue this alternation until emergency medical services (EMS) arrives, the victim shows signs of life such as normal breathing or movement, or the AED battery depletes. Common errors, such as placing pads over jewelry or pacemakers, can reduce effectiveness and should be avoided by following the device's diagrams and prompts precisely.[54][57]
Deployment and Accessibility
Placement Strategies
Effective placement of automated external defibrillators (AEDs) in public spaces prioritizes locations with high foot traffic and elevated risk of out-of-hospital cardiac arrest (OHCA), such as airports, schools, and sports venues, to ensure rapid access within critical minutes. In airports, AEDs are commonly installed in terminals and high-traffic zones to cover passenger areas efficiently. Schools often position AEDs near athletic facilities, cafeterias, and main hallways to protect students and staff during daily activities and events. Sports venues, including stadiums and arenas, deploy AEDs centrally near spectator seating and playing fields to address potential incidents during games or practices.[58][59][60]In private settings, AED placement focuses on workplaces and homes, particularly for high-risk individuals, to bridge gaps in emergency response times. Workplaces, such as office buildings and manufacturing sites, benefit from AEDs located in central, accessible areas like break rooms or near elevators, as encouraged by the American Heart Association to enhance employee safety. For homes, the Mayo Clinic recommends AEDs for those at high risk of sudden cardiac arrest, such as individuals with prior heart conditions, placing the device in an easily reachable spot like a bedroom or living area for immediate family use.[36][61]To optimize accessibility, AEDs require clear mapping, signage, and strategic density planning. Apps like PulsePoint enable crowdsourced registration and real-time tracking of AED locations, alerting nearby users during emergencies and integrating with 911 systems for efficient deployment. Signage guidelines emphasize visible, standardized placement, such as wall-mounted cabinets at 7 feet above the ground with universal AED symbols, directional arrows, and illuminated indicators to guide bystanders quickly. The American Heart Association advises placing AEDs to ensure a rescuer can reach one within a 3- to 5-minute round-trip walk from anywhere in the area to maximize coverage and utilization potential.[62][63][35]
Regulatory Requirements
In the United States, automated external defibrillators (AEDs) are classified by the Food and Drug Administration (FDA) as Class III medical devices, which are high-risk devices intended to sustain or support life.[64] This classification mandates premarket approval (PMA) to ensure safety and effectiveness before market entry, a requirement that became effective in 2015 following a regulatory transition from prior grandfathered Class II status.[65]Globally, AEDs must adhere to international standards such as IEC 60601-2-4, which specifies basic safety and essential performance requirements for cardiac defibrillators, including automated models, to mitigate risks like electrical hazards and ensure reliable operation.[66] The World Health Organization (WHO) supports the integration of AEDs into emergency care frameworks as part of broader guidelines on essential emergency equipment.[67]Regulatory mandates for AED availability vary by jurisdiction but increasingly require placement in high-risk public venues. In the U.S., as of 2025, approximately 24 states mandate AEDs in public schools (with numbers increasing via recent legislation), and 14 states require them in health clubs and gyms to enhance accessibility during cardiac events. Recent U.S. federal efforts, including CDC grants, support AED placement in schools.[68][69][70] In the European Union, public access programs promote widespread AED deployment, with several member states enacting laws requiring AEDs in public buildings and sports facilities since 2018 to facilitate bystander intervention; EU initiatives aim for standardized public access by 2025.[71][72]AED owners and manufacturers are subject to registration and adverse event reporting obligations to monitor device performance and safety. In the U.S., the FDA requires reporting of deaths, serious injuries, or malfunctions via the Medical Device Reporting (MDR) system under 21 CFR Part 803, with initial reports due within 30 calendar days of awareness to enable timely corrective actions.[73] Voluntary reporting through MedWatch is also encouraged for users to document issues with AEDs or accessories.[1]
Maintenance Protocols
Automated external defibrillators (AEDs) incorporate built-in self-testing mechanisms to monitor key components and ensure operational readiness. These devices automatically conduct diagnostics on a daily, weekly, and monthly basis, evaluating battery voltage and charge, electrode pad integrity and connection, and internal circuitry functionality. Such self-tests alert users via visible indicators, audible alarms, or voice prompts if issues are detected, allowing for prompt intervention without manual initiation.[61][74]In addition to automated self-tests, manual scheduled checks are essential for comprehensive maintenance. Program coordinators or designated personnel should perform visual inspections at least monthly—or weekly in high-usage environments—using a standardized checklist to verify the AED's status indicator shows readiness, confirm no physical damage or corrosion, ensure pads and batteries are within expiration dates, and check for any alarms or error messages. These inspections supplement manufacturer guidelines and help maintain compliance with regulatory standards. Quarterly reviews may include more detailed assessments, such as testing the unit's power-on function and documenting findings in a maintenance log.[74][1]Battery and electrode pad replacement follows manufacturer-specified intervals to prevent degradation. Batteries typically last 2 to 5 years in standby mode, with many models alerting users near expiration; replacement is required upon depletion or after use if shocks are delivered. Electrode pads, which have a shelf life of 2 to 4 years, must be swapped out at expiration or immediately post-use, as they are single-use items. Keeping spare pads and batteries on hand ensures minimal downtime during replacements.[61][9]Proper environmental protection is critical to AED longevity and performance. Devices should be stored in conditions avoiding extremes, with recommended storage temperatures ranging from -30°C to 70°C (-22°F to 158°F) and operating temperatures from 0°C to 50°C (32°F to 122°F); exposure to temperatures outside these ranges can compromise battery life or electronics. Relative humidity should be maintained between 10% and 95% non-condensing to prevent moisture-related corrosion or pad adhesive failure. AEDs must be kept in clean, dry, accessible cabinets away from direct sunlight, dust, or vibrations.[9][75]Following an incident, post-use protocols involve immediate restocking and evaluation to restore the AED to full readiness. Used pads must be replaced, and if the battery was expended, it requires swapping; the device should then undergo a full self-test and, if necessary, professional servicing by the manufacturer to inspect for damage or download event data. All uses must be logged with details like date, time, and outcomes, and reported to local emergency medical services (EMS) for follow-up analysis, which may inform program improvements. With adherence to these maintenance routines, AED failure rates remain low, typically under 2%, significantly enhancing reliability during emergencies.[74][76]
Effectiveness and Impact
Clinical Benefits and Evidence
The Public Access Defibrillation (PAD) trial, a multicenter randomized controlled study conducted in 2004, demonstrated significant clinical benefits of bystander AED use in out-of-hospital cardiac arrest (OHCA). In this trial involving lay responders trained to use AEDs alongside CPR in high-risk public settings, survival to hospital discharge was 23% in the AED group compared to 14% in the CPR-only group, highlighting the device's role in enabling rapid defibrillation by non-medical personnel.[77] This improvement underscores AEDs' capacity to double survival rates in shockable rhythms when applied promptly by bystanders.[78]Meta-analyses of observational and interventional studies further affirm the broader impact of public AED access on OHCA outcomes. A 2017 systematic review of public access defibrillation programs reported a median survival rate of 40% for OHCA patients treated with bystander AEDs, representing a substantial increase over traditional EMS-only responses.[34] More recent data from the 2025 American Heart Association guidelines, synthesizing global registries and trials up to 2024, indicate that widespread public AED deployment is associated with approximately a three-fold increase in survival to hospital discharge for witnessed OHCA with shockable rhythms, driven by higher rates of early defibrillation.[79]Advancements in AED technology, particularly the adoption of biphasic waveforms, have enhanced defibrillation efficacy compared to earlier monophasic designs. A 2016 Cochrane systematic review of randomized trials found that biphasic shocks achieved higher first-shock success rates for terminating VF in both in-hospital and out-of-hospital settings, with a risk ratio of approximately 1.19 for success (derived from failure RR 0.84, 95% CI 0.70-1.01).[80] This superiority stems from the waveform's optimized energy delivery, reducing post-shock myocardial dysfunction while maintaining high termination rates.[81]Despite these benefits, AEDs have inherent limitations in certain OHCA scenarios. Shockable rhythms such as VF or pulseless ventricular tachycardia account for only about 20-25% of initial OHCA presentations, with the majority involving non-shockable rhythms like asystole or pulseless electrical activity, where AEDs provide no therapeutic shock and survival relies primarily on CPR and advanced care.[82] In non-VF cases, AED application may inadvertently delay other interventions, though devices are designed not to shock non-shockable rhythms, minimizing harm.[83]
Survival Statistics
Out-of-hospital cardiac arrests (OHCA) represent a major global health challenge, with automated external defibrillators (AEDs) playing a critical role in improving survival when deployed promptly. For witnessed ventricular fibrillation (VF) arrests, survival rates can reach approximately 70% if defibrillation occurs within 3 minutes of collapse, as emphasized in longstanding American Heart Association (AHA) guidelines updated through 2025.[4] This high efficacy underscores the time-sensitive nature of AED intervention, where each minute of delay reduces survival by 7-10%.[4]In the United States, approximately 350,000 OHCA events occur annually, with nearly 90% resulting in fatality without immediate intervention.[84] Bystander AED use in public settings has been shown to double or triple survival rates compared to cases without defibrillation, achieving around 35% survival to hospital discharge when applied early.[6] For instance, in communities with public access defibrillation programs, survival after VF arrest rises significantly, from a baseline of around 9% without AED to 24-38% with bystander application.[6]Survival disparities persist across demographics and geographies. In rural areas, OHCA survival rates range from 8-10%, compared to 15-25% in urban settings, largely due to longer response times and limited AED accessibility.[85][82] Pediatric survival following OHCA is approximately 19% overall with AED use, though rates remain lower at 6-9% without prompt intervention.[86]Recent trends indicate progress driven by awareness campaigns. Reports from 2024-2025 highlight increased bystander confidence in CPR (from 33% to 39%), attributed to initiatives like the AHA's Nation of Lifesavers and World Restart a Heart campaigns, which have boosted public training participation.[87]
One notable example of AED effectiveness in a public venue occurred during the January 2, 2023, NFL game between the Buffalo Bills and Cincinnati Bengals, where Bills safety Damar Hamlin suffered sudden cardiac arrest after a tackle-induced commotio cordis. On-field medical staff promptly initiated CPR and applied an AED, delivering a shock that restored his sinus rhythm within minutes, enabling his stabilization, hospital discharge after nine days, and eventual return to professional play.[88] This case, witnessed by millions, underscored the life-saving potential of immediate AED access in high-profile sports events and spurred national advocacy for expanded AED deployment.[89]In home settings, AED accessibility has proven transformative, as illustrated by a 2023 case in Ohio where a 10-year-old boy, Isaiah Bangoura, suffered sudden cardiac arrest while at home; his family's quick use of a home AED alongside CPR restored his heart rhythm, leading to full recovery and highlighting the value of residential AEDs for pediatric emergencies.[90] Such incidents emphasize how home AEDs bridge critical response gaps, particularly for children at higher risk from undiagnosed conditions like long QT syndrome.[91]Despite these successes, challenges persist, including user errors that can compromise outcomes. In a 2022 incident aboard an American Airlines flight, a 14-year-old passenger went into cardiac arrest, but the onboard AED failed to deliver a shock due to an uncharged battery—a maintenance oversight by the crew—resulting in the teen's death despite CPR efforts.[92] Similarly, a documented case of pad misplacement during resuscitation placed electrodes below the diaphragm, creating an ineffective electrical vector that delayed effective defibrillation and caused unnecessary discomfort, illustrating how improper application can hinder AED utility.[93]Post-event analyses from these and similar incidents reveal key lessons, including the need for immediate AED accessibility to minimize response times—ideally under three minutes—and comprehensive training to prevent errors like misreading prompts or incorrect pad adhesion.[94] Regular drills and closed-loop communication among responders have been shown to enhance proficiency, ensuring AEDs fulfill their potential in diverse real-world contexts.[95]Globally, OHCA affects ~70,000 annually in Europe with ~10% survival, improved to 20-30% in areas with robust PAD programs. Emerging technologies like smartphone apps for AED mapping have increased bystander use by up to 62% in trials, while drone delivery pilots (as of 2025) reduce response times by 5-10 minutes in rural areas.[96]
Legal and Ethical Aspects
Liability Protections
Good Samaritan laws in the United States provide legal immunity from civil liability to individuals who use or attempt to use an automated external defibrillator (AED) in good faith during a perceived medical emergency, provided the action does not involve gross negligence or willful misconduct.[97] These protections encourage bystanders and lay rescuers to intervene without fear of lawsuits, extending to both users and those who acquire, own, or maintain AEDs as long as they comply with applicable guidelines.[98] All 50 states and the District of Columbia have enacted such legislation, often modeled on broader Good Samaritan principles that shield rescuers from claims of ordinary negligence.[99]The U.S. Cardiac Arrest Survival Act of 2000, enacted as part of Public Law 106-505, further strengthens these safeguards by amending the Public Health Service Act to offer federal liability protections for the acquisition, placement, and good-faith use of AEDs in public settings.[100] This legislation promotes widespread AED deployment by ensuring that state and local governments, as well as other entities, are immune from civil suits related to emergency use, except in cases of gross negligence, thereby addressing barriers to public access defibrillation programs.[101]To incentivize AED ownership, several states offer tax credits for purchases, such as New York's credit of up to $500 per unit, which applies to individuals and businesses acquiring devices for emergency use.[102] Owners and providers also receive liability immunity for maintenance activities when following manufacturer-recommended protocols and documentation standards, minimizing risks associated with device upkeep.[74]Ethically, the duty to intervene with an AED arises from the principle of beneficence in emergency care, where the potential benefits of restoring cardiac rhythm outweigh the minimal risks of intervention, especially given legal protections that mitigate harm from non-action in life-threatening situations like sudden cardiac arrest.[103]
International Variations
In Canada, provincial Good Samaritan legislation mirrors U.S. protections by offering immunity from civil liability for those providing emergency assistance, including AED deployment, as long as actions are performed in good faith without gross negligence; examples include Ontario's Good Samaritan Act and similar statutes in British Columbia and Quebec.[104] These laws apply to both laypersons and off-duty professionals across provinces, promoting widespread AED accessibility. At the provincial level, pilot programs for AED registries emerged in 2025, such as the AED Foundation's virtual mapping initiative integrating with 911 services in Ontario and Prince Edward Island's voluntary online registry, aimed at locating devices during cardiac arrests.[105][106]Australia's Civil Liability Acts, enacted at the state and territory levels, grant Good Samaritans immunity from personal civil liability when rendering emergency aid, including AED use, provided the assistance is gratuitous and not grossly negligent; this applies nationwide under frameworks like New South Wales' Civil Liability Act 2002.[107] In recent years, states have begun mandating AED installation in high-risk public venues, such as South Australia's requirement for defibrillators in buildings like schools, sports facilities, and prisons, with the legislation passing in 2022 as the first such mandate.[108]In Europe and the United Kingdom, the European Union's efforts toward harmonization via directives on medical device regulations have facilitated AED deployment, but Good Samaritan protections remain inconsistent across member states, with some countries like France enacting specific AED immunity laws in 2020 while others, such as certain Eastern European nations, offer limited or no explicit safeguards for lay rescuers.[109] In the UK, no dedicated Good Samaritan statute exists for AED use, but common law, the Social Action, Responsibility and Heroism Act 2015, and guidelines from the Resuscitation Council provide de facto protection against liability for reasonable emergency actions, though off-duty professionals may face narrower scopes in some scenarios compared to volunteers.[110][111] This patchwork approach contrasts with more uniform protections in North America, leading to varied bystander willingness to intervene.In developing countries, liability protections for AED users are often limited or absent, with few nations enacting comprehensive Good Samaritan laws, which discourages public access and use amid resource constraints.[112] Instead, international efforts emphasize donation programs to bridge gaps; organizations like Project C.U.R.E. and the World Health Organization distribute AEDs to low-resource areas, such as the 2024 donation of 40 devices to Iran's emergency services, focusing on training and placement in community health centers without formal legal incentives.[113][114]
Historical Development
Early Inventions
The origins of defibrillation technology trace back to the mid-20th century, when efforts to restore cardiac rhythm focused on direct interventions during surgery. In 1947, cardiothoracic surgeon Claude S. Beck achieved the first successful defibrillation of a human heart using alternating current (AC) applied directly to the exposed organ during an open-chest procedure on a 14-year-old patient whose heart had entered ventricular fibrillation amid congenital defect repair.[115] This landmark event, performed at Case Western Reserve University in Cleveland, Ohio, built on Beck's prior animal experiments and marked the initial clinical application of electrical countershock to reverse fibrillation, though limited to intraoperative settings.[116]Advancements in the 1950s and 1960s shifted toward external, non-invasive methods and portability, driven by research into ventricular fibrillation (VF) mechanisms. Paul M. Zoll pioneered closed-chest defibrillation in 1956, using AC shocks delivered through large electrodes on the chest, which expanded treatment beyond the operating room but carried risks of skin burns and myocardial damage due to the prolonged AC waveform.[117] Concurrently, extensive animal studies, particularly on dogs, elucidated VF induction and reversal; for instance, William B. Kouwenhoven's team at Johns Hopkins University demonstrated in the late 1950s that direct current (DC) shocks could effectively defibrillate closed-chest models with fewer complications than AC, reporting successful restoration in over 90% of induced VF cases using capacitor-discharge pulses of 400-1,000 joules.[118] These experiments, published in journals like the Journal of Applied Physiology, established DC as a safer standard and paved the way for human applications.[119]A pivotal step toward field use occurred in 1966, when Northern Irish cardiologist Frank Pantridge developed and deployed the first portable defibrillator in Belfast ambulances, weighing approximately 70 kg and powered by car batteries for DC delivery.[120] This device enabled pre-hospital treatment of out-of-hospital cardiac arrests, dramatically reducing response times; its inaugural use on January 1, 1966, highlighted the feasibility of ambulance-based defibrillation, influencing global emergency protocols.[121] Prior to automated external defibrillators (AEDs), all devices remained manual, necessitating real-time electrocardiogram (ECG) interpretation and operation by trained physicians or paramedics, which restricted access in non-clinical environments.[117]
Key Milestones and Advancements
The development of automated external defibrillators (AEDs) in the 1970s marked a pivotal shift toward devices capable of basic rhythm analysis without requiring advanced medical training. Early efforts in the decade included microprocessor-based rhythm analysis by researchers such as Archie Sherbaniuk and Henry Montgomery, simplifying use for non-experts and leading to Physio-Control's release of the first commercial AED in 1980.[4] Building on this, Richard E. Kerber and colleagues advanced AED research in the early 1980s, demonstrating the feasibility of automated systems in detecting ventricular fibrillation and delivering shocks in prehospital settings. A 1988 study by Weaver et al. showed comparable outcomes to manual defibrillators, with survival rates to hospital discharge of 17% for AED use versus 13% for manual methods in out-of-hospital cardiac arrest cases.[122]By the 1990s, AEDs transitioned from prototypes to commercially viable tools for public access, culminating in U.S. Food and Drug Administration (FDA) approval for layperson use in 1996, which expanded deployment beyond healthcare professionals. Physio-Control released the LIFEPAK 300 AED in 1991, but the 1996 approval specifically enabled widespread public programs by confirming safety and ease of use for untrained rescuers. This regulatory milestone facilitated initial installations in airports, stadiums, and other high-risk venues, reducing barriers to early defibrillation.[123]The 2000s saw significant technological refinements, particularly the adoption of biphasic waveforms, which improved shock efficacy at lower energy levels compared to monophasic designs, achieving up to 90% success rates in terminating ventricular fibrillation. This advancement, integrated into AEDs by manufacturers like Philips and Zoll, reduced device size and battery requirements while enhancing portability. Concurrently, the American Heart Association (AHA) issued 2004 guidelines endorsing public access defibrillation (PAD) programs, following the landmark Public Access Defibrillation Trial that showed a 74% increase in survival when trained lay responders used AEDs within community sites. These guidelines spurred national PAD initiatives, integrating AED training into CPR courses and promoting site-specific programs in schools and workplaces.[4]In the 2010s and 2020s, AEDs incorporated smartphone integration to enhance accessibility, with apps like PulsePoint (launched in 2010) alerting nearby users to cardiac arrests and guiding them to the closest registered devices via GPS, potentially halving response times in urban areas. Global registries proliferated to map AED locations, such as the Cardiac Arrest Registry to Enhance Survival (CARES) in the U.S., which by 2020 covered nearly 2,000 communities and tracked over 150,000 out-of-hospital cardiac arrests annually, and international efforts like the European Registry of Cardiac Arrest (EuReCa), enabling real-time dispatcher integration for bystander activation. In 2025, the AHA hosted a symposium on AED access expansion, recommending strategies like mandatory public placements in high-traffic areas and leveraging mobile technology for nationwide registries to address gaps in low-access regions, aiming to boost out-of-hospital survival rates beyond current 10% benchmarks.[124]
Future Innovations
Emerging Technologies
Recent advancements in artificial intelligence (AI) are significantly enhancing the capabilities of automated external defibrillators (AEDs) by improving rhythm detection speed and accuracy. Machine learning algorithms integrated into AEDs enable real-time analysis of electrocardiogram (ECG) signals, achieving sensitivity rates exceeding 95% for shockable rhythms such as ventricular fibrillation.[125] These AI enhancements also incorporate noise reduction techniques to filter out artifacts from motion or environmental interference, allowing for more reliable performance in chaotic emergency settings.[126] For instance, convolutional neural network models have demonstrated up to 98% sensitivity in classifying arrhythmias, potentially reducing decision times and improving survival outcomes.[127]Connectivity features powered by Internet of Things (IoT) technology are transforming AED deployment by enabling real-time tracking and automated emergency notifications. Modern AED models, such as the Avive Connect, which received FDA approval, use cellular and GPS integration to pinpoint device locations and automatically alert emergency services like 911 upon activation.[128] This allows dispatchers to guide bystanders to the nearest unit and remotely monitor usage, with pilots showing reduced response times in urban and public spaces.[129] As of 2025, these connected systems facilitate seamless integration with public safety networks, enhancing coordination during out-of-hospital cardiac arrests.[128] In November 2025, an American Heart Association study demonstrated the feasibility and safety of manual nighttime AED drone delivery using lights and infrared technology, achieving performance comparable to daytime operations.[130]Integration with wearable technologies is bridging the gap between preventive and responsive defibrillation. Wearable cardioverter defibrillators (WCDs), like the FDA-cleared Jewel Patch in 2025, provide continuous monitoring and deliver AED-like shocks for at-risk patients, offering a non-invasive alternative to implants.[131] These devices complement traditional AEDs by alerting nearby public units via apps during events, while drone delivery pilots in rural areas—such as those in James City County, Virginia, and Denmark—aim to dispatch AEDs within minutes to remote locations.[132][133]Advanced features are further evolving AED usability and accessibility. Real-time CPR feedback, as in ZOLL's AED 3, uses accelerometers to provide audio and visual guidance on compression depth and rate, improving rescuer performance without prior training.[134] Multilingual AI-driven voice prompts, available in models like the Cardiac Science Powerheart G5, support dual-language instructions (e.g., English and Spanish) to accommodate diverse users, with options for up to 14 languages in some units.[135] Additionally, solar-powered storage cabinets, such as the AED Protect, ensure AED readiness in off-grid or outdoor environments by maintaining optimal temperatures without reliance on mains electricity.[136]
Challenges and Global Access Issues
One significant barrier to the widespread adoption of automated external defibrillators (AEDs) is their cost, with standard models typically priced between $1,400 and $2,500, depending on features and accessories. This expense, combined with ongoing maintenance costs for batteries and pads, often deters deployment in low-income regions and resource-limited settings, where healthcare budgets prioritize basic infrastructure over advanced emergency devices. In developing countries, limited public funding exacerbates this issue, resulting in sparse AED availability and contributing to lower survival rates from out-of-hospital cardiac arrest (OHCA).[137]Awareness gaps further hinder effective AED utilization, as bystander intervention rates remain low despite their potential to double survival odds in shockable rhythms. Studies indicate that bystander AED use occurs in only 2% to 5% of OHCA cases, primarily due to fear of misuse, lack of training, and unawareness of nearby device locations. These factors are compounded by inadequate public education campaigns, leading to hesitation even when AEDs are accessible, and underscoring the need for targeted training to build confidence among lay responders.[138]Equity issues manifest in stark disparities across demographics and geographies, with urban areas boasting higher AED density—such as 63.8% of registered devices in one analysis—compared to rural regions, where coverage can be as low as 36.2%, resulting in longer retrieval times and poorer outcomes. Pediatric access poses additional challenges, as financial and insurance barriers limit home AED placement for at-risk children, despite evidence that early defibrillation improves survival in this group. Environmental factors, including extreme climates, also affect reliability; high temperatures above 122°F can degrade battery life and cause electrode pads to lose adhesion due to gel evaporation, while sub-freezing conditions impair electronic functions, necessitating climate-controlled storage that is often unavailable in remote or low-resource areas.[139][140][141]Addressing these challenges requires robust policy interventions, including subsidies to offset acquisition costs and international standards to harmonize deployment and maintenance protocols. Recent analyses of global legislation reveal that only 48% of jurisdictions mandate AEDmaintenance in public and private spaces, highlighting the urgency for expanded frameworks like those proposed in international resuscitation guidelines to promote equitable access.[142] In November 2025, bipartisan legislation, the Public Access to Defibrillation in Transportation Facilities Act of 2025, was introduced in the United States to expand AED access in transportation hubs, aiming to address equity gaps for millions of travelers.[143] Calls for subsidized programs, particularly in low- and middle-income countries, aim to bridge these gaps by integrating AEDs into broader emergency care strategies.