[转帖]除颤仪相关背景知识--英文

Automated external defibrillator

An automated external defibrillator, open and ready for pads to be attached

The International Liaison Committee on Resuscitation universal AED sign

An automated external defibrillator or AED is a portable electronic device that automatically diagnoses the potentially life threatening cardiac arrhythmias of ventricular fibrillation and ventricular tachycardia in a patient,^[1] and is able to treat them through defibrillation, the application of electrical therapy which stops the arrhythmia, allowing the heart to reestablish an effective rhythm.

AEDs are designed to be simple to use for the layman, and the use of AEDs is taught in many first aid, first responder and basic life support (BLS) level CPR classes.^[2]

Contents [hide] [hide] 1 Usage 2 Placement 3 Preparation for operation 4 Mechanism of operation 5 Simplicity of use 6 Liability 7 References 8 External links

 Usage

An automated external defibrillator is used in cases of life threatening cardiac arrhythmias which have led to cardiac arrest. The rhythms the device will treat are usually limited to:

• Ventricular fibrillation (shortened to VF or V-Fib)
• Pulseless Ventricular tachycardia (shortened to VT or V-Tach)^[1]

AEDs, like all defibrillators, are not designed to shock asystole ('flat line' patterns) as this will not have a positive clinical outcome. The asystolic patient only has a chance of survival if, through a combination of CPR and cardiac stimulant drugs, one of the shockable rhythms can be established, which makes it imperative for CPR to be carried out prior to the arrival of a defibrillator.

In each of the two types of shockable cardiac arrhythmia, the heart is active, yet in a life-threatening, dysfunctional pattern. In ventricular fibrillation, the electrical activity of the heart becomes chaotic, preventing the ventricle from effectively pumping blood. In ventricular tachycardia, the heart beats too fast to effectively pump blood. Ultimately, ventricular tachycardia leads to ventricular fibrillation. The fibrillation in the heart decreases over time, and will eventually reach asystole.

Uncorrected, these cardiac conditions rapidly lead to irreversible brain damage and death. After approximately three to five minutes, ^[3]irreversible brain/tissue damage may begin to occur. For every minute that a person in cardiac arrest goes without being successfully treated (by defibrillation), the chance of survival decreases by 10 percent.^[4]

AEDs are designed to be used by laypersons who ideally should have received AED training. This is in contrast to more sophisticated manual and semi-automatic defibrillators used by health professionals, which can act as a pacemaker if the heart rate is too slow (bradycardia) and perform other functions which require a skilled operator able to read electrocardiograms.

Bras with a metal underwire and piercings on the torso must be removed before using the AED on someone to avoid interference.^[5]

 Placement

An AED at a railway station in Japan. The AED box has information on how to use it in Japanese, English, Chinese and Korean. Station staff are trained to use it as well.

Automated external defibrillators are generally either held by trained personnel who will attend events or are public access units which can be found in places including corporate and government offices, shopping centres, airports, restaurants, casinos, hotels, sports stadiums, schools and universities, community centers, fitness centers, health clubs, workplaces and any other location where people may congregate.

The location of a public access AED should take in to account where large groups of people gather, regardless of age or activity. Children as well as adults may fall victim to sudden cardiac arrest (SCA)

In many areas, emergency vehicles are likely to carry AEDs, with some ambulances carrying an AED in addition to manual defibrillators. Police or fire vehicles often carry an AED for first responder use. Some areas have dedicated community first responders, who are volunteers tasked with keeping an AED and taking it to any victims in their area. AEDs are also increasingly common on commercial airlines, cruise ships, and other transportation facilities.

In order to make them highly visible, public access AEDs often are brightly colored, and are mounted in protective cases near the entrance of a building. When these protective cases are opened or the defibrillator is removed, some will sound a buzzer to alert nearby staff to their removal, though this does not necessarily summon emergency services; trained AED operators should know to phone for an ambulance when sending for or using an AED. In September 2008, the International Liaison Committee on Resuscitation issued a 'universal AED sign' to be adopted throughout the world to indicate the presence of an AED, and this is shown at the top of this page.^[6]

A trend that is developing is the purchase of AEDs to be used in the home, particularly by those with known existing heart conditions.^[7] The number of devices in the community has grown as prices have fallen to affordable levels. There has been some concern among medical professionals that these home users do not necessarily have appropriate training,^[8] and many advocate the more widespread use of community responders, who can be appropriately trained and managed.

Typically, an AED kit will contain a face shield for providing a barrier between patient and first aider during rescue breathing; a pair of nitrile rubber gloves; a pair of trauma shears for cutting through a patient's clothing to expose the chest; a small towel for wiping away any moisture on the chest, and a razor for shaving those with very hairy chests.^[9]

 Preparation for operation

An AED at Chūbu Centrair International Airport in Aichi, Japan.

Most manufacturers recommend checking the AED before every period of duty or on a regular basis for fixed units. Some units need to be switched on in order to perform a self check; other models have a self check system built in with a visible indicator.^{[citation needed]}

All manufacturers mark their pads with an expiry date, and it is important to ensure that the pads are in date. This is usually marked on the outside of the pads. Some models are designed to make this date visible through a 'window', although others will require the opening of the case to find the date stamp.^{[citation needed]}

 Mechanism of operation

The use of easily visible status indicator and pad expiration date on one model of AED

An AED is external because the operator applies the electrode pads to the bare chest of the victim, as opposed to internal defibrillators, which have electrodes surgically implanted inside the body of a patient.

Automatic refers to the unit's ability to autonomously analyse the patient's condition, and to assist this, the vast majority of units have spoken prompts, and some may also have visual displays to instruct the user.

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 electrical current.

When charged, the device instructs the user to ensure no one is touching the victim 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 victim and either instruct that CPR 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^{[citation needed]} to monitor the actions taken by the personnel in order to ascertain if these had any impact on the survival outcome. All this recorded data can be either downloaded to a computer or printed out so that the providing organisation or responsible body is able to see the effectiveness of both CPR and defibrillation.

AEDs available to the public may be semi-automatic or fully automatic. Fully automatic units are likely to have few buttons, often activating as soon as the case is opened, and possibly just one button to shock, or in some cases this will be performed automatically. The user has no input in the operation of the unit apart from attaching the pads and following the prompts. Health care professionals and other trained responders may use a semi-automatic defibrillator, which is likely to have an ECG readout display, and the possibility to override the rhythm analysis software. This allows trained personnel to provide a higher level of care.

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.^[10]

 Simplicity of use

Usual placement of pads on chest

Unlike regular defibrillators, an automated external defibrillator requires minimal training to use. It automatically diagnoses the heart rhythm and determines if a shock is needed. Automatic models will administer the shock without the user's command. Semi-automatic models will tell the user that a shock is needed, but the user must tell the machine to do so, usually by pressing a button. In most circumstances, the user cannot override a "no shock" advisory by an AED. Some AEDs may be used on children - those under 55 lbs (25 kg) in weight or under age 8. If a particular model of AED is approved for pediatric use, all that is required is the use of more appropriate pads. Some organizations, such as the American Heart Association, recommend that if pediatric AED pads are not available, adult pads should be used to determine if the child is in a shockable rhythm. There is insufficient evidence to suggest that a child, in a shockable cardiac arrest, can be "hurt" by an adult defibrillation energy setting.^{[citation needed]}

All AEDs approved for use in the United States use an electronic voice to prompt users through each step. Because the user of an AED may be hearing impaired, many AEDs now include visual prompts as well. Most units are designed for use by non-medical operators. Their ease of use has given rise to the notion of public access defibrillation (PAD), which experts agree has the potential to be the single greatest advance in the treatment of out-of-hospital cardiac arrest since the invention of CPR.^[11]

 Liability

Automated external defibrillators are now easy enough to use that most states in the United States include the "good faith" use of an AED by any person under the Good Samaritan laws.^[12] "Good faith" protection under a Good Samaritan law means that a volunteer responder (not acting as a part of one's occupation) cannot be held civilly liable for the harm or death of a victim by providing improper or inadequate care, given that the harm or death was not intentional and the responder was acting within the limits of their training and in good faith. In the United States, Good Samaritan laws provide some protection for the use of AEDs by trained and untrained responders.^[13] AEDs create little liability if used correctly;^{[citation needed]} NREMT-B and many state EMT training and many CPR classes incorporate or offer AED education as a part of their program. In addition to Good Samaritan laws, Ontario, Canada also has the "Chase McEachern Act (Heart Defibrillator Civil Liability), 2007 (Bill 171 – Subsection N)", passed in June, 2007,^[14] which protects individuals from liability for damages that may occur from their use of an AED to save someone's life at the immediate scene of an emergency unless damages are caused by gross negligence.

 References

1. ^ ^{a b} 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 (1997). "Automatic External Defibrillators for Public Access Defibrillation". Circulation (American Heart Association) 95 (1677-1682): 1677. PMID 9118556. https://circ.ahajournals.org/cgi/content/full/95/6/1677. Retrieved on 2007-06-28. 
2. ^ "CPR Adult Courses". American Red Cross. https://www.redcross.org/services/hss/courses/adultcpraed.html. Retrieved on 2007-06-28. 
3. ^ "Cardiopulmonary Resuscitation (CPR) Statistics". American Red Cross. https://www.americanheart.org/presenter.jhtml?identifier=4483. Retrieved on 2008-10-27. 
4. ^ American Red Cross. CPR/AED for the Professional Rescuer (participant's manual). Yardley, PA: StayWell, 2006. (page 63).
5. ^ de Vries, Lloyd (2006-03-22). "Breathing Easier". CBS News. https://www.cbsnews.com/stories/2006/03/22/opinion/garver/main1429483.shtml. Retrieved on 2009-04-22. "We got a short lesson in using an AED, which is an Automated External Defibrillator. We had the thrill of yelling, "Clear!" Unfortunately this also brought on a little anxiety when Sean mentioned if the patient were a woman with a metal underwire in her bra or with metal piercings on her torso, we'd have to remove them." 
6. ^ "ILCOR presents a universal AED sign". European Resuscitation Council. https://www.erc.edu/index.php/newsItem/en/nid=204/. 
7. ^ "Heartstart Home Defibrillator". Philips Electronics. https://www.heartstarthome.com/content/why_defibrillators/why_defibs2_detail.asp. Retrieved on 2007-06-15. 
8. ^ Barnaby, Barnaby J (2005-05-03). "Do It Yourself: The Home Heart Defibrillator". https://www.nytimes.com/2005/05/03/business/03jolt.html?ei=5088&en=84d7afacd0fd7943&ex=1272772800&partner=rssnyt&emc=rss&pagewanted=all&position=. Retrieved on 2007-06-15. 
9. ^ CPR/AED for the Professional Rescuer, supra, page 65 ("[a] safety surgical razor should be included in the AED kit.") The other items not directly mentioned in this text but are used in AED preparation, such as the gloves (used throughout patron assessment) and the towel, as the chest should be dried prior to AED pad attachment (id, at page 64).
10. ^ "AED Plus Biphasic Waveform". ZOLL Medical Corporation. https://www.zoll.com/product_resource.aspx?id=728. Retrieved on 2008-10-27. 
11. ^ Introduction to the International Guidelines 2000 for CPR and ECC
12. ^ Laws on Cardiac Arrest and Defibrillators, 2008 update. National Conference of State Legislatures. Retrieved on 2008-03-23.
13. ^ State Laws on Heart Attacks, Cardiac Arrest & Defibrillators
14. ^ Health System Improvement Act, 2007 Retrieved on 26 June 2007

 External links

• American Heart Association: Learn & Live
• American Red Cross: Saving a Life is as Easy as A-E-D
• FDA Heart Health Online: Automated External Defibrillator (AED)
• Resuscitation Council (UK)

Defibrillation View of defibrillator position and placement, using hands free electrodes. Defibrillation is the definitive treatment for the life-threatening cardiac arrhythmias, ventricular fibrillation and pulseless ventricular tachycardia. Defibrillation consists of delivering a therapeutic dose of electrical energy to the affected heart with a device called a defibrillator. This depolarizes a critical mass of the heart muscle, terminates the arrhythmia, and allows normal sinus rhythm to be reestablished by the body's natural pacemaker, in the sinoatrial node of the heart.
Defibrillators can be external, transvenous, or implanted, depending on the type of device used or needed. Some external units, known as automated external defibrillators (AEDs), automate the diagnosis of treatable rhythms, meaning that lay responders or bystanders are able to use them successfully with little, or in some cases no training at all.
Contents  1 History 1.1 Closed-chest method 1.2 Move to direct current 1.3 Portable units become available 1.4 Change to a biphasic waveform 1.5 Implantable devices 2 Types 2.1 Manual external defibrillator 2.2 Manual internal defibrillator 2.3 Automated external defibrillator (AED) 2.4 Semi-automated external defibrillators 2.5 Implantable Cardioverter-defibrillator (ICD) 2.6 Wearable Cardiac Defibrillator 3 Modelling Defibrillation 4 Interface with the patient 4.1 Placement 5 Popular culture references 6 See also 7 References 8 External links //
 History Defibrillation was first demonstrated in 1899 by Prevost and Batelli, two physiologists from University of Geneva, Switzerland. They discovered that small electric shocks could induce ventricular fibrillation in dogs, and that larger charges would reverse the condition.
The first use on a human was in 1947 by Claude Beck,[1] professor of surgery at Case Western Reserve University. Beck's theory was that ventricular fibrillation often occurred in hearts which were fundamentally healthy, in his terms "Heart too good to die", and that there must be a way of saving them. Beck first used the technique successfully on a 14 year old boy who was being operated on for a congenital chest defect. The boy's chest was surgically opened, and manual cardiac massage was undertaken for 45 minutes until the arrival of the defibrillator. Beck used internal paddles on either side of the heart, along with procainamide, a heart drug, and achieved return of normal sinus rhythm.
These early defibrillators used the alternating current from a power socket, transformed from the 110-240 volts available in the line, up to between 300 and 1000 volts, to the exposed heart by way of 'paddle' type electrodes. The technique was often ineffective in reverting VF while morphological studies showed damage to the cells of the heart muscle post mortem. The nature of the AC machine with a large transformer also made these units very hard to transport, and they tended to be large units on wheels.

 Closed-chest method Until the early 1950s, defibrillation of the heart was possible only when the chest cavity was open during surgery. The technique used an alternating current from a 300 or greater volt source delivered to the sides of the exposed heart by 'paddle' electrodes where each electrode was a flat or slightly concave metal plate of about 40 mm diameter. The closed-chest defibrillator device which applied an alternating current of greater than 1000 volts, conducted by means of externally applied electrodes through the chest cage to the heart, was pioneered by Dr V. Eskin with assistance by A. Klimov in Frunze, USSR in mid 1950s.[2]

 Move to direct current A circuit diagram showing the simplest (non-electronically controlled) defibrillator design, depending on the inductor (damping), producing a Lown, Edmark or Gurvich Waveform In 1959 Bernard Lown commenced research into an alternative technique which involved charging of a bank of capacitors to approximately 1000 volts with an energy content of 100-200 joules then delivering the charge through an inductance such as to produce a heavily damped sinusoidal wave of finite duration (~5 milliseconds) to the heart by way of 'paddle' electrodes. The work of Lown was taken to clinical application by engineer Barouh Berkovits with his "cardioverter".
The Lown waveform, as it was known, was the standard for defibrillation until the late 1980s when numerous studies showed that a biphasic truncated waveform (BTE) was equally efficacious while requiring the delivery of lower levels of energy to produce defibrillation. A side effect was a significant reduction in weight of the machine. The BTE waveform, combined with automatic measurement of transthoracic impedance is the basis for modern defibrillators.

 Portable units become available A major breakthrough was the introduction of portable defibrillators used out of the hospital. This was pioneered in the early 1960s by Prof. Frank Pantridge in Belfast. Today portable defibrillators are among the many very important tools carried by ambulances. They are the only proven way to resuscitate a person who has had a cardiac arrest unwitnessed by EMS who is still in persistent ventricular fibrillation or ventricular tachycardia at the arrival of pre-hospital providers.
Gradual improvements in the design of defibrillators, and partly based on the work developing implanted versions (see below) have lead to the availability of Automated External Defibrillators, which can analyse the heart rhythm by themselves, diagnosing the shockable rhythms, and then charging to treat. This means that no clinical skill is required in their use, allowing lay people to respond to emergencies effectively.

 Change to a biphasic waveform Until the late 1980s, external defibrillators delivered a Lown type waveform (see Bernard Lown) which was a heavily damped sinusoidal impulse having a mainly uniphasic characteristic. Biphasic defibrillation, however, alternates the direction of the pulses, completing one cycle in approximately 10 milliseconds. Biphasic defibrillation was originally developed and used for implantable cardioverter-defibrillators. When applied to external defibrillators, biphasic defibrillation significantly decreases the energy level necessary for successful defibrillation. This, in turn, decreases risk of burns and myocardial damage.
Ventricular fibrillation (VF) could be returned to normal sinus rhythm in 60% of cardiac arrest patients treated with a single shock from a monophasic defibrillator. Most biphasic defibrillators have a first shock success rate of greater than 90%.[3]

 Implantable devices A further development in defibrillation came with the invention of the implantable device, known as an implantable cardioverter-defibrillator (or ICD). This was pioneered at Sinai Hospital in Baltimore by a team that included Stephen Heilman, Alois Langer, Jack Lattuca, Morton Mower, Michel Mirowski, and Mir Imran, with the help of industrial collaborator Intec Systems of Pittsburgh[4]. Mirowski teamed up with Mower and Staewen, and together they commenced their research in 1969 but it was 11 years before they treated their first patient. Similar developmental work was carried out by Schuder and colleagues at the University of Missouri.
The work was commenced, despite doubts amongst leading experts in the field of arrhythmias and sudden death. There was doubt that their ideas would ever become a clinical reality. In 1972 Bernard Lown, the inventor of the external defibrillator, stated in the journal Circulation - "The very rare patient who has frequent bouts of ventricular fibrillation is best treated in a coronary care unit and is better served by an effective antiarrhythmic program or surgical correction of inadequate coronary blood flow or ventricular malfunction. In fact, the implanted defibrillator system represents an imperfect solution in search of a plausible and practical application."
The problems to be overcome were the design of a system which would allow detection of ventricular fibrillation or ventricular tachycardia. Despite the lack of financial backing and grants, they persisted and the first device was implanted in February 1980 at Johns Hopkins Hospital by Dr. Levi Watkins, Jr. Modern ICDs do not require a thoracotomy and possess pacing, cardioversion, and defibrillation capabilities.
The invention of implantable units is invaluable to some regular sufferers of heart problems, although they are generally only given to those people who have already had a cardiac episode.

 Types
 Manual external defibrillator External defibrillator / monitor The units are used in conjunction with (or more often have inbuilt) electrocardiogram readers, which the healthcare provider uses to diagnose a cardiac condition (most often fibrillation or tachycardia although there are some other rhythms which can be treated by different shocks). The healthcare provider will then decide what charge (in joules) to use, based on proven guidelines and experience, and will deliver the shock through paddles or pads on the patient's chest. As they require detailed medical knowledge, these units are generally only found in hospitals and on some ambulances. For instance, every NHS ambulance in the United Kingdom is equipped with a manual defibrillator for use by the attending paramedics and technicians. In the United States, many advanced EMTs and all paramedics are trained to recognize lethal arrhythmias and deliver appropriate electrical therapy with a manual defibrillator when appropriate.

 Manual internal defibrillator These are the direct descendants of the work of Beck and Lown. They are virtually identical to the external version, except that the charge is delivered through internal paddles in direct contact with the heart. These are almost exclusively found in operating theatres, where the chest is likely to be open, or can be opened quickly by a surgeon.

 Automated external defibrillator (AED) Main article: Automated external defibrillator An AED at a railway station in Japan. The AED box has information on how to use it in Japanese, English, Chinese and Korean, and station staff are trained to use it. These simple-to-use units are based on computer technology which is designed to analyze the heart rhythm itself, and then advise the user whether a shock is required. They are designed to be used by lay persons, who require little training to operate them correctly. They are usually limited in their interventions to delivering high joule shocks for VF (ventricular fibrillation) and VT (ventricular tachycardia) rhythms, making them generally limiting for use by health professionals, who could diagnose and treat a wider range of problems with a manual or semi-automatic unit.
The automatic units also take time (generally 10–20 seconds) to diagnose the rhythm, where a professional could diagnose and treat the condition far quicker with a manual unit.[5] These time intervals for analysis, which require stopping chest compressions, have been shown in a number of studies to have a significant negative effect on shock success.[6] This effect led to the recent change in the AHA defibrillation guideline (calling for two minutes of CPR after each shock without analyzing the cardiac rhythm) and some bodies recommend that AEDs should not be used when manual defibrillators and trained operators are available.[5]
Automated external defibrillators are generally either held by trained personnel who will attend incidents, or are public access units which can be found in places including corporate and government offices, shopping centres, airports, restaurants, casinos, hotels, sports stadiums, schools and universities, community centers, fitness centers and health clubs.
An automated external defibrillator, open and ready for pads to be attached The locating of a public access AED should take in to account where large groups of people gather, and the risk category associated with these people, to ascertain whether the risk of a sudden cardiac arrest incident is high. For example, a center for teenage children is a particularly low risk category (as children very rarely enter heart rhythms such as VF(Ventricular Fibrillation or VT(Ventricular Tachycardia), being generally young and fit, and the most common cause of pediatric cardiac arrest is trauma - where the heart is more likely to enter asystole or PEA, where an AED is of no use), whereas a large office building with a high ratio of males over 50 is a very high risk environment.
In many areas, emergency services vehicles are likely to carry AEDs, with some ambulances carrying an AED in addition to a manual unit. In addition, some police or fire service vehicles carry an AED for first responder use. Some areas have dedicated community first responders, who are volunteers tasked with keeping an AED and taking it to any victims in their area. It is also increasingly common to find AEDs on transport such as commercial airlines and cruise ships.
In order to make them highly visible, public access AEDs often are brightly coloured, and are mounted in protective cases near the entrance of a building. When these protective cases are opened, and the defibrillator removed, some will sound a buzzer to alert nearby staff to their removal but do not necessarily summon emergency services. All trained AED operators should also know to phone for an ambulance when sending for or using an AED, as the patient will be unconscious, which always requires ambulance attendance.

 Semi-automated external defibrillators These units are a compromise between a full manual unit and an automated unit. They are mostly used by pre-hospital care professionals such as paramedics and emergency medical technicians. These units have the automated capabilities of the AED but also feature an ECG display, and a manual override, where the clinician can make their own decision, either before or instead of the computer. Some of these units are also able to act as a pacemaker if the heart rate is too slow (bradycardia) and perform other functions which require a skilled operator.

 Implantable Cardioverter-defibrillator (ICD) Main article: Implantable cardioverter-defibrillator Also known as automatic internal cardiac defibrillator (AICD). These devices are implants, similar to pacemakers (and many can also perform the pacemaking function). They constantly monitor the patient's heart rhythm, and automatically administer shocks for various life threatening arrhythmias, according to the device's programming. Many modern devices can distinguish between ventricular fibrillation, ventricular tachycardia, and more benign arrhythmias like supraventricular tachycardia and atrial fibrillation. Some devices may attempt overdrive pacing prior to synchronised cardioversion. When the life threatening arrhythmia is ventricular fibrillation, the device is programmed to proceed immediately to an unsynchronized shock.
There are cases where the patient's ICD may fire constantly or inappropriately. This is considered a medical emergency, as it depletes the device's battery life, causes significant discomfort and anxiety to the patient, and in some cases may actually trigger life threatening arrhythmias. Some emergency medical services personnel are now equipped with a ring magnet to place over the device, which effectively disables the shock function of the device while still allowing the pacemaker to function (if the device is so equipped). If the device is shocking frequently, but appropriately, EMS personnel may administer sedation.

 Wearable Cardiac Defibrillator A development of the AICD is a portable external defibrillator that is worn like a vest.[7] The unit monitors the patient 24 hours a day and will automatically deliver a biphasic shock if needed. This device is mainly indicated in patients awaiting an implantable defibrillator. Currently only one company manufactures these and they are of limited availability.

 Modelling Defibrillation The efficacy of a cardiac defibrillator is highly dependent on the position of its electrodes. Most internal defibrillators are implanted in octogenarians, but a few children need the devices. Implanting defibrillators in kids is particularly difficult because children are small, will grow over time, and possess cardiac anatomy that differs from that of adults. Recently, researchers were able to create a software modeling system capable of mapping an individual’s thorax and determining the optimal position for an external or internal cardiac defibrillator.[citation needed]
With the help of pre-existing surgical planning applications, the software uses myocardial voltage gradients to predict the likelihood of successful defibrillation. According to the critical mass hypothesis, defibrillation is effective only if it produces a threshold voltage gradient in a large fraction of the myocardial mass. Usually, a gradient of three to five volts per centimeter is needed in 95 % of the heart. Voltage gradients of over 60 V/cm can damage tissue. The modeling software seeks to obtain safe voltage gradients above the defibrillation threshold.
Early simulations using the software suggest that small changes in electrode positioning can have large effects on defibrillation, and despite engineering hurdles that remain, the modeling system promises to help guide the placement of implanted defibrillators in children and adults.
Recent mathematical models of defibrillation are based on the bidomain model of cardiac tissue. [8] Calculations using a realistic heart shape and fiber geometry are required to determine how cardiac tissue responds to a strong electrical shock.

 Interface with the patient The most well-known type of electrode (widely depicted in films and television) is the traditional metal paddle with an insulated (usually plastic) handle. This type must be held in place on the patient's skin while a shock or a series of shocks is delivered. Before the paddle is used, a gel must be applied to the patient's skin, in order to ensure a good connection and to minimize electrical resistance, also called chest impedance (despite the DC discharge). These are generally only found on the manual external units.
Newer types of resuscitation electrodes are designed as an adhesive pad. These are peeled off their backing and applied to the patient's chest when deemed necessary, much the same as any other sticker. These electrodes are then connected to a defibrillator. If defibrillation is required, the machine is charged, and the shock is delivered, without any need to apply any gel or to retrieve and place any paddles. These adhesive pads are found on most automated and semi-automated units, and are gradually replacing paddles entirely in non-hospital settings.
Both solid- and wet-gel adhesive electrodes are available. Solid-gel electrodes are more convenient, because there is no need to clean the patient's skin after removing the electrodes. However, the use of solid-gel electrodes presents a higher risk of burns during defibrillation, since wet-gel electrodes more evenly conduct electricity into the body.
Some adhesive electrodes are designed to be used not only for defibrillation, but also for transcutaneous pacing and synchronized electrical cardioversion.
While the paddles on a monitor/defibrillator may be quicker than using the patches, adhesive patches are superior due to their ability to provide appropriate EKG tracing without the artifact visible from human interference with the paddles. Adhesive electrodes are also inherently safer than the paddles for the operator of the defibrillator to use, as they minimize the risk of the operator coming into physical (and thus electrical) contact with the patient as the shock is delivered, by allowing the operator to stand several feet away. Adhesive patches also require no force to remain in place and deliver the shock appropriately, wheras paddles require approximately 25lbs of force to be applied while the shock is delivered.[Citation Needed]

 Placement Anterio-apical placement of external defibrillator electrodes (When defibrillation is unsuccessful, anterio-posterior placement is also sometimes attempted) Resuscitation electrodes are placed according to one of two schemes. The anterior-posterior scheme (conf. image) is the preferred scheme for long-term electrode placement. One electrode is placed over the left precordium (the lower part of the chest, in front of the heart). The other electrode is placed on the back, behind the heart in the region between the scapula. This placement is preferred because it is best for non-invasive pacing.
The anterior-apex scheme can be used when the anterior-posterior scheme is inconvenient or unnecessary. In this scheme, the anterior electrode is placed on the right, below the clavicle. The apex electrode is applied to the left side of the patient, just below and to the left of the pectoral muscle. This scheme works well for defibrillation and cardioversion, as well as for monitoring an ECG.

 Popular culture references Lists of miscellaneous information should be avoided. Please relocate any relevant information into appropriate sections or articles. (October 2007) In the television series Emergency!, firefighters often used defibrillators, with their 'catchphrase' being the standard warning (still used to this day) of yelling "Clear!" right before applying the shock, to warn everyone around to stay away from the patient for risk of electrical shock.
In the same series, the defibrillator induces a sudden, violent jerk or convulsion by the patient; in reality, although the muscles may contract, such dramatic patient presentation is rare. Most television shows will have the medical provider defibrillate the "flat-line" ECG rhythm (also known as asystole); this is not done in real life. Only the cardiac arrest rhythms ventricular fibrillation and pulseless ventricular tachycardia are normally defibrillated. (There are also several heart rhythms that can be "shocked" when the patient is not in cardiac arrest, such as supraventricular tachycardia or ventricular tachycardia that produces a pulse; this procedure is known as cardioversion, not defibrillation.)
In an episode of M*A*S*H ("Heroes"), B.J. Hunnicutt is credited with being the first to use a defibrillator in a human patient, after reading a journal article about its use in dogs. This was in the second-to-last season (1982), which would have put the usage around 1952, five years after it was actually used in humans.
In Australia up until the 1990s, it was quite rare for an ambulance to carry a defibrillator. This changed in 1990 when Australian media mogul Kerry Packer had a heart attack and the ambulance that responded to the call did carry a defibrillator. After this, Kerry Packer donated a large sum to the Ambulance Service of New South Wales in order that all ambulances in New South Wales should be fitted with a personal defibrillator, which is why defibrillators in Australia are colloquially called "Packer Whackers". [9]
In the 1989 film The Abyss, Lindsey Brigman (Mary Elizabeth Mastrantonio) drowns and her ex-husband Bud (Ed Harris) restarts her heart with a defibrillator.
In the 1996 movie Eraser, Johnny Casteleone (Robert Pastorelli), is repeatedly shocked with a defibrillator unnecessarily, in a hospital emergency room.
In the NBC television series E.R., the defibrillator is used regularly. As the show puts a high value on medical realism, classic mistakes such as defibrillating asystole ("flat-line") rarely occur.
In the movie Mission Impossible 3, defibrillators were said to deactivate explosive charges implanted into the protagonist's head. On one occasion, a portable defibrillator could not recharge in time to save Ethan's partner. On another occasion, Ethan himself was implanted. In a potentially fatal maneuver, he received a defibrillator-like shock from open-circuit, high-voltage wires, and regains consciousness after a dramatic revival/flashback sequence.

 See also Cardiopulmonary resuscitation (CPR) Advanced cardiac life support (ACLS) Cardioversion Implantable cardioverter-defibrillator Automated external defibrillator Myocardial infarction (heart attack) Ambulance
 References ^ "Claude Beck, defibrillation and CPR". Case Western Reserve University. https://www.case.edu/artsci/dittrick/site2/museum/artifacts/group-c/c-8defrib.htm. Retrieved on 2007-06-15.  ^ Sov Zdravookhr Kirg.. "Some results with the use of the DPA-3 defibrillator (developed by V. Ia. Eskin and A. M. Klimov) in the treatment of terminal states" (in Russian). https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=5880446&dopt=Abstract. Retrieved on 2007-08-26.  ^ Heart Smarter: EMS Implications of the 2005 AHA Guidelines for ECC & CPR pp 15-16 ^ https://www3.interscience.wiley.com/journal/118913850/abstract?CRETRY=1&SRETRY=0 ^ a b Immediate Life Support: Second Edition. Resuscitation Council UK. 2006. ISBN 1-903812-12-7.  ^ Eftestol T, Sunde K, Steen PA. Effects of interrupting precordial compressions on the calculated probability of defibrillation success during out-of-hospital cardiac arrest. Circulation 2002;105:2270-3 ^ "What is the LifeVest?". Zoll Lifecor. https://www.zoll.lifecor.com/about_lifevest/about.asp. Retrieved on 2009-02-09.  ^ Trayanova N (2006). "Defibrillation of the heart: insights into mechanisms from modelling studies". Experimental Physiology 91: 323-337.  ^ "Defibrillation". Farlex, Inc.. https://medical-dictionary.thefreedictionary.com/Packer+Whacker. Retrieved on 2009-04-21.  Picard, André (2007-04-27). "School defibrillators could be lifesavers". The Globe and Mail. https://www.theglobeandmail.com/servlet/story/RTGAM.20070427.wxldefib27/BNStory/specialScienceandHealth/home. Retrieved on 2008-06-20. 
 External links Sudden Cardiac Arrest Foundation Center for Integration of Medicine and Innovative Technology American Red Cross: Saving a Life is as Easy as A-E-D FDA Heart Health Online: Automated External Defibrillator (AED) Resuscitation Council (UK) History of defibrillation How an internal defibrillator is implanted from Children's Hospital Heart Center, Seattle.

日本的火车站里都有这种应急除颤装置？？太厉害了。看来在一些发达国家，除颤仪和消防栓一样一样的普及。以人为本啊。