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Defibrillation is a technique used in emergency medicine to save lives when the heart is in an abnormal or damaging rhythm. The most common indications for emergency defibrillation is for ventricular fibrillation and ventricular tachycardia.
Often, ventricular fibrillation is preceded by ventricular tachycardia. While these are both fast rhythms in the lower chambers of the heart (the left and right ventricles), ventricular tachycardia is a more organized rhythm, while ventricular fibrillation is described as chaotic activity of the ventricles. While ventricular tachycardia can lead to ventricular fibrillation, it may break on its own, allowing the person's normal rhythm to resume. Ventricular fibrillation never breaks on its own, and will always lead to death if it is not terminated quickly. Ventricular tachycardia may be associated with an adequate blood pressure to perfuse the brain. Often, however, the heart is beating too fast for blood to enter the heart, causing a low blood pressure and decreased perfusion of the brain and other vital organs. In ventricular fibrillation, since the electrical activity in the ventricle is chaotic, there's no organized pumping of blood, and therefore there is no blood perfusion of the brain.
The purpose of defibrillation of ventricular arrhythmias is to apply a controlled electrical shock to the heart, which leads to depolarization of the entire electrical conduction system of the heart. When the heart repolarizes, the normal electrical conduction may assert itself, in which case the ventricular arrhythmia is terminated. However, if enough energy is not used for defibrillation, the heart may not be completely depolarized, in which case the ventricular tachycardia or fibrillation may not be terminated. Also, if the heart itself is not getting enough oxygen or if there is an instability of the electrolytes in the cardiac cells, the ventricular arrhythmia may recur.
If there is no electrical activity in the heart (electrical asystole, or standstill), then the heart is already depolarized, and defibrillation will have no effect.
Although the process of defibrillation can be repeated, the number of attempts is, in practice, limited, to a series of three or four attempts at increasing voltages, as the likelihood of restoring normal heart rhythm is much less in successive attempts.
Increasingly, automated external defibrillators (AEDs) are being made available at airports, shopping centres, etc.
Defibrillators can also be implanted ( implantable cardioverter-defibrillators or ICDs) in people at high risk of developing an arrhythmia. The ICD is rather like an artificial pacemaker, and indeed performs all the functions of a pacemaker, but it can also deliver a defibrillation shock if a dangerous arrhythmia is detected.
In 1899, Prevost and Batelli Physiologists working at the university of Geneva while ascertaining the voltage and current required to induce ventricular fibrillation in the dog, discovered that they could defibrillate a dog’s heart to sinus rhythm by applying an appropriate high current countershock directly to the surface of the myocardium by directly applying electrodes - "…we have shown that the fibrillatory tremulations produced in the dog, in which they are definitely established can under certain circumstances be arrested, the heart re-established its beats, if one submits the animal to passages of a high current of high voltage (of 4800 volts, for example)" [Prevost JL et al. 1899]. The impetus to further work into the relationships between cardiac syncope and dysrhythmias had begun in the late 19th century. It is interesting to look at the driving forces behind this. The two main reasons were the growing concerns over unexpected sudden deaths due to the increasing use of chloroform anaesthesia which had been introduced many years before in 1847 and the growing pervasiveness of electrification particularly in urban areas and the occurrence of accidental electrocution especially in those workers involved in building the electrical distribution network [Fye WB 1985]. With the increase in electrification and in the interest of safety, five committees were set up to address the problem of accidental deaths due to electrocution. To fund this they were provided, in 1932, with a grant from the electrical distributor Con Edison. One of these committees, chaired by John Howell was under a mandate to investigate the physiological phenomena surrounding electrocution. This result was that a team comprising Kouwenhoven, an electrical engineer, Hooker, a physiologist and Langworthy a neurologist who were all staff at Johns Hopkins. They were presented with the challenge of approving or disproving the claims of defibrillation by Batelli and Prevost made at the turn of the century [Kouwenhoven WB 1969]. At this time, Wiggers held the chair of physiology at the Western Reserve University at Cleveland. He was asked by Howell to get involved. There was already in Cleveland an interest in cardiac resuscitation that had been initiated by Guthrie. Guthrie, the previous incumbent had a brother who died of electrocution. Wiggers had been working in this area of research since his appointment as Professor of Physiology in 1918. Their contribution to the basic knowledge of defibrillation and management of cardiac arrest was exceptional. Kouwenhoven contributed three major landmarks. He confirmed the earlier work of Prevost and Batelli, that an electric shock could indeed reverse ventricular fibrillation. He developed some of the earliest defibrillation devices initially using 60 Hz AC and subsequently DC shocks to defibrillate. He was also involved in the introduction of early methods of external cardiac massage [Kouwenhoven WB 1969]. In 1946 two Russian workers, Gurvich and Yuniev reported the successful restoration of regular rhythm in the fibrillating mammalian heart with capacitor charges applied externally across the closed chest [Gurvich NL et al. 1946]. In 1947 Beck, Pritchard and Feil reported the first case of successful defibrillation of the human heart with full recovery [Kouwenhoven WB et al. 1954].
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