An automated external defibrillator (AED) is a portable electronic device that automatically diagnoses the life-threatening cardiacarrhythmias of ventricular fibrillation and ventricular tachycardia in a patient, and is able to treat them through defibrillation. Defibrillation is the application of electrical therapy which stops the arrhythmia, allowing the heart to reestablish an effective rhythm.
An AED is “automatic (automated)” because of the unit’s ability to autonomously analyse the patient’s condition. To assist this, the vast majority of units have spoken prompts, and some may also have visual displays to instruct the user.
“External” refers to the fact that 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).
The heart has an internal electrical system that controls the rate and rhythm of the heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The process repeats with each new heartbeat.
Problems with the electrical system can cause abnormal heart rhythms called arrhythmias. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Some arrhythmias can cause the heart to stop pumping blood to the body. These arrhythmias cause SCA (Sudden cardiac arrest).
Sudden cardiac arrest is one of the leading causes of death in the U.S. It can happen to anyone, anytime, anywhere and at any age. An AED is the only effective treatment for restoring a regular heart rhythm during sudden cardiac arrest and is an easy to operate tool for someone with no medical background.
The 2010 consensus on science for CPR and Emergency Cardiovascular Care (ECC) agrees that Sudden Cardiac Arrest can be treated most effectively by a combination of CPR and Defibrillation.
Mechanism of operating aed (automated external defibrillator)
When 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 electric current.
When 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 another shock.
Many 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 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.
The 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.
“AED Plus Biphasic Waveform”. ZOLL Medical Corporation. Retrieved 2008-10-27
Kerber, Richard E; Becker, Lance B; Bourland, Joseph D; Cummins, Richard O; Hallstrom, Alfred P; Michos, Mary B; Nichol, Graham; Ornato, Joseph P; Thies, William H; White, Roger D; Zuckerman, Bram D (March 18, 1997). “Automatic External Defibrillators for Public Access Defibrillation”. Circulation. American Heart Association. 95 (1677–1682): 1677–82. doi:10.1161/01.cir.95.6.1677. PMID 9118556. Archived from the original on 8 June 2007. Retrieved 2007-06-28.
“ZOLL® AED Plus® Package w/Voice Recording – AED Superstore – 20, 20100001101011010, 20100001101011010 with Extras, 20100001102011010, 2010000110201101”. AED Superstore. Retrieved 2016-05-12.
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