Defibrillation - defibrillator
Defibrillation is the definitive treatment for the life-threatening cardiac arrhythmias, ventricular fibrillation and 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. Some external units, known as automated external defibrillators or AED , 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.
Cardiac arrhythmia
Cardiac arrhythmia also known as dysrhythmia is a term for any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.
Some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest and sudden death. Others cause aggravating symptoms such as an abnormal awareness of heart beat or palpitations, and may be merely annoying. Others may not be associated with any symptoms at all, but pre-dispose toward potentially life threatening stroke or embolus.
Some arrhythmias are very minor and can be regarded as normal variants. In fact, most people will sometimes feel their heart skip a beat, or give an occasional extra strong beat - neither of which is usually a cause for alarm.
The term sinus arrhythmia refers to a normal phenomenon of mild acceleration and slowing of the heart rate that occurs with breathing in and out. It is usually quite pronounced in children, and steadily lessens with age. This can also present during meditation breathing exercises that involve deep inhalings and breath holdings patterns.
Ventricular fibrillation
Ventricular fibrillation or V-fib or VF is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them tremble rather than contract properly. Ventricular fibrillation is a medical emergency. If the arrhythmia continues for more than a few seconds, blood circulation will cease, and death may occur in a matter of minutes.
Ventricular tachycardia
Ventricular tachycardia or V-tach or VT is a tachycardia, or fast heart rhythm that originates in one of the ventricles of the heart. This is a potentially life-threatening arrhythmia because it may lead to ventricular fibrillation and sudden death. Less commonly, however, some forms of this arrhythmia appear benign, especially in young individuals.
History of Defibrillation and defibrillator
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, 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 procaine amide, 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.
Move to direct current
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 in ambulances. This was pioneered in the early 1960s by Prof. Frank Pantridge in Belfast. Today portable defibrillators are one of the most 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 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 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%.
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 including Stephen Heilman, Alois Langer, Morton Mower, Michel Mirowski, and Mir Imran, with the help of industrial collaborator Intec Systems of Pittsburgh. 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.
Source - http://www.wikipedia.org
Portable units become available
A major breakthrough was the introduction of portable defibrillators in ambulances. This was pioneered in the early 1960s by Prof. Frank Pantridge in Belfast. Today portable defibrillators are one of the most 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 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 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%.
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 including Stephen Heilman, Alois Langer, Morton Mower, Michel Mirowski, and Mir Imran, with the help of industrial collaborator Intec Systems of Pittsburgh. 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.
Source - http://www.wikipedia.org
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