What is an AED?

An AED, or automated external defibrillator, is a small, portable device which analyzes the heart's rhythm and prompts the user to deliver a defibrillation shock if it determines one is needed. The AED is an uncomplicated device having one or two control buttons and a pair of self-stick electrode pads which are placed on the victim's bare chest. Once turned on, the AED guides the user through each step of the defibrillation process by providing voice or visual prompts (or both).

The AED is designed to detect two shockable heart rhythms-Ventricular Fibrillation (VF), and rapid Ventricular Tachycardia (VT). An AED does not require critical care expertise or sophisticated medical training to operate; it is not even necessary for the user to be able to identify the specific arrhythmia. Analyzing the heart's electrical function is programmed into the computerized device. When the AED detects either of these two arrhythmias, the machine charges and prompts the user to push the button to administer the shock, sending a lifesaving pulse of electrical current to the heart. AED's will not allow a shock to be delivered unless the victim requires a shock. In fact, the AED records all cardiac arrhythmias in its data storage centre.

AED's have always been small devices, but now they are about the size of a hardback novel and are extremely portable, simple and easy to use. When compared to defibrillators intended for use by advanced health care providers—doctors, nurses and paramedics-AED's require minimal medical knowledge to operate, thereby enabling non-medical professionals to respond skilfully to SCA emergencies. With the technological advance in AED design and use, more first responders are capable of administering life-saving early defibrillation to victims of Sudden Cardiac Arrest.
At one time, only medical professionals with advanced training in heart rhythm interpretation could perform defibrillation. Now, anyone with CPR/AED training can give potentially lifesaving treatment using an AED. Specially designed for easy use by a first rescuer, the AED requires minimal training. (The first rescuer is anyone who arrives on the scene first—an emergency medical services worker, a firefighter or police officer, or a layperson with minimal training in the use of an AED.) In fact, in mock cardiac arrest drills, untrained sixth grade children used AED's without difficulty—proving that virtually anyone with even minimal training can save a life. It's that easy._xii

The Chain of Survival

Because early defibrillation could save over 50,000 lives per year in North America, the American Heart Association (AHA) and the Heart and Stroke Foundation of Canada (HSFC) advocate the widespread public use of AED's. In 1990, the AHA introduced a treatment model called The Chain of Survival which graphically describes the sequence of events required for a favourable outcome when SCA strikes.

The core of the Chain's sequential links are:

• early access to emergency services
• early CPR
• early defibrillation
• early advanced care

The American Heart Association and the Heart and Stroke Foundation of Canada both endorse this model to help us understand how to increase the survival of SCA victims. The Chain of Survival is only as strong as its weakest link. Early defibrillation has been termed the "critical link."^xiii

Early Access to the emergency medical services system means someone has witnessed the event, recognized the emergency, decided to help, confirms the victim is unresponsive, and then calls for help by dialling 9-1-1 or the local emergency number.

According to the National Emergency Number Association, nearly 93 percent of the population of the United States is covered by some form of 9-1-1 service, either basic or enhanced coverage. Ninety-five percent of that coverage is enhanced 9-1-1 which identifies the calling location automatically. Approximately 96 percent of the geographic US is covered by some type of 9-1-1.^xiv Canada has also adopted the 9-1-1 emergency telephone number, which has near universal implementation nationally. Other countries may use different emergency numbers, though typically they are three digit numbers. For example, in New Zealand, the emergency number is 1-1-1; Australia's is 0-0-0; the European Union's is 1-1-2; Great Britain's is 9-9-9. Some countries have a different emergency number for each of the different emergency services; these often differ only by the last number. Know the local telephone number to access emergency services.

Early CPR or cardiopulmonary resuscitation is administered, by an individual trained in this simple emergency procedure, to a person who has stopped breathing or whose heart has stopped beating. In the event of sudden cardiac arrest, CPR buys time by keeping the victim's blood oxygenated and flowing to the heart and brain. Early CPR can double a SCA victim's chance of survival if it's begun before defibrillation, but only defibrillation has the potential to actually save the victim's life.

Early Defibrillation has been called the critical link in the Chain of Survival because the elapsed time from collapse to defibrillation is the key indicator of survival from sudden cardiac arrest. Rapid defibrillation has been proven to be the critical medical intervention for sudden cardiac arrest, the single most important factor affecting survival from SCA in adults. Typically, someone trained in defibrillation treats the cardiac arrest victim using an AED. The goal is to stabilize the heart with early defibrillation before the paramedics arrive to begin early advanced care.

Defibrillation, as an essential component of emergency cardiac care, stabilizes an irregular heartbeat or restores normal heart rhythm after a cardiac arrest. After defibrillation, SCA patients sometimes experience a temporary irritation or a mild sunburn-like sensation in the chest area where the shocks were applied. This sensation usually disappears within 24 hours.^xv

Early Advanced Care is the treatment which follows early defibrillation and is administered by trained providers who have arrived to administer lifesaving interventions. Advanced lifesaving interventions include advanced airway therapies and breathing management and administering intravenous drugs. These procedures stabilize patients before they arrive for in-hospital advanced cardiac care.

In-hospital care may include medications to regulate arrhythmias or, if medication cannot regulate the heart rhythm, a small implantable cardioverter defibrillator or ICD may be recommended. This device is implanted in the patient's body to monitor electrical activity in the patient's heart. Able to sense abnormal heart rhythms, and within seconds of detecting fibrillation, the ICD delivers a biphasic shock to the heart to restore its normal rhythm. Many survivors of SCA receive the implantable defibrillator.

To summarize, the ideal response plan follows the Chain of Survival: recognize the SCA incident early, call 9-1-1, start CPR, apply an AED if you have one on site, or wait for Emergency Services to arrive, have paramedics administer Advanced Cardiac Life Support (ACLS) and finally, rehabilitate. With these links in place we have the best chance of survival from SCA. Much has improved in the areas of early recognition, early access, and early CPR-all as a result of the many combined CPR and AED training courses offered throughout the world. Today, AED's are becoming the universal standard of care.

A Brief History of the Evolution of Emergency Medical Services

For many years the medical community has recognized the need to take certain medical procedures and specific treatments out of hospital settings and into the community. A brief history of the evolution in Emergency Medical Services reveals the logical development of some of those tools, including the automated external defibrillator. By understanding something of this history, we can appreciate the development of public access defibrillation programs.

Since ancient times, physicians in western cultures have committed their services by taking the Hippocratic Oath which affirmed their ethical conduct and obligations to their patients. From earliest times in medical history up to the late 1960s, most medical practitioners felt obligated to provide their patients and communities with personalized, after-hours home medical care and visitation services or "house calls." Today, medical doctors rarely visit patients outside hospitals, walk-in clinics, or their private practice offices.

Key factors which shifted this centuries-old practice were many and included: massive fiscal budget deficits; changes to universal health care management and philosophy; costly liability and insurance coverage for physicians (especially as it pertains to medical acts performed in a home setting); increased growth in patient–physician ratios; increased workloads; restraints and/or restrictions in allowable government billing practices; and attrition of physicians leaving the health care sector.

These changes radically impacted the general wellness of society and generated major gaps in healthcare service delivery. With these changes came an imminent need to augment the scope of tasks performed by physicians with an alternatively-trained professional able to co-assist in providing quality patient care and treatment—a trained medical provider skilled in delivering lifesaving procedures.

As medicine and health care advanced, and with the critical care experiences learned from the war in Vietnam, we witnessed the evolution of a new level of community health care provided by Emergency Medical Technicians and Paramedics. Quickly, the physicians' goal became to provide firefighters and paramedics with advanced life support training—thus filling the void created by the lack of physician house calls. Medical technology rushed to meet this goal, resulting in the development of medical wonder tools such as portable heart monitor defibrillators, endotracheal tubes, and medications which could be administered by EMS personnel. At this time, we began to see CPR being taught to laypersons.

The Emergence of the Automated External Defibrillator and Its Implications

As pre-hospital advanced life support evolved, statistical data was collected, and it became more evident that early recognition and early defibrillation of Sudden Cardiac Arrest played a significant role in saving lives. Turning this knowledge into a goal, the research and development of the Automated External Defibrillator (AED) began in the 1980's.

For almost twenty years, emergency rescue personnel have used machines to provide early defibrillation outside of the hospital in communities throughout the US and Canada. Because paramedic training is expensive and time consuming, basic cardiac life support training with the use of AED's was targeted at EMT's and firefighters. It wasn't until the early 1990's, however, that the medical community considered expanding the first-responder group to the public and began the development of the public access AED programs.

Unlike the early models of defibrillators intended for use by advanced healthcare providers such as doctors, nurses, and paramedics, contemporary AED's do not require rescuers to have extensive medical knowledge to understand and operate them. Today, the expertise needed to analyze the heart's electrical function is programmed right into the device, enabling non-medical professionals to respond to cardiac emergencies. This permits a much larger group of first responders to administer life saving defibrillations to patients of SCA.

On a daily basis, the AED continues to evolve, getting smaller, easier to use and ever more popular. It has become so user-friendly and simple to administer that the medical, legal and political communities are now beginning to put their full support behind its use in potentially high risk and highly populated areas. Before long, AED's will be placed in all public areas, becoming as common as fire extinguishers. Dr. W.D. Weaver of Detroit's Henry Ford Heart Institute said, "I think there's enough evidence that these devices should be in every public place, and ultimately…in every home."^xvi

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