The defibrillation and cardioversion belong to a countershock (EIT). This two types of EIT at all their similarity, have essential distinctions as the defibrillation represents the procedure of stopping of fibrillation of ventricles by means of drawing electric discharge and it concerns the major a resuscitation action, in cardioversion is a way of treatment of tachyarrhythmias which essence consists in the termination of circulation of excitement in a myocardium by drawing electric discharge in a certain phase of a cardial cycle. While the electric defibrillation - always the emergency manipulation, cardioversion is planned when restoration of a rhythm at a stable hemodynamics is made, at the prepared patient, at inefficiency of other ways of treatment, and emergency when cardioversion is carried out at paroxysms of tachyarrhythmias with an unstable hemodynamics and resistant to other ways of therapy.
Carrying out cardioversion demands synchronization when drawing an impulse happens at the time of registration of a tooth of R. Drawing the category in other phase of a cardial cycle can result in inefficiency of the procedure or to development of complications up to fibrillation of ventricles.
If to speak about history, then electric methods of treatment of arrhythmias and heart blocks, originate already from the second half of the 18th century and the first documented case of use of electric impulses for assistance at sudden death belongs to July 16, 1774 when the resident of the London region of Soho tried to help the three-year-old girl who fell from the first floor, using categories of electricity of the Leiden cans. The case was successful and in the subsequent scientists began to study a defibrillation. In 1947 the American surgeon Claude Beck carried out a successful defibrillation during an operative measure on heart. Creation of scientific bases for understanding of a countershock and also the first serious experiments in this area were made by Paul Zoll. In 1960 Bernard Laun developed the first defibrillator of a direct current. This defibrillator became the first in the line of modern devices of this kind. Also the cardioversion method was offered them.
There are many hypotheses which try to explain the mechanism of action of a defibrillation, but any of them does not explain it fully. The basic is the postulate that a main objective of a defibrillatory impulse is restoration of synchronization of reductions of cardiomyocytes in way their cutting and simultaneous depolarization. There is so-called "recharge" which in the conditions of safety of a pacemaker (pacemaker) leads to restoration of a warm rhythm.
When carrying out a countershock use of the category of such form and size is important at the same time to gain the defibrillating effect (the category of too small size on the contrary has aritmogenny effect) and at the same time to put as smaller damage is possible for a myocardium. In this regard distinguish single-phase and bi-phase impulses. The single-phase impulse is a monopolar impulse when current has only one direction. It is realized in the majority of old models of defibrillators. Obtaining due effect when carrying out a defibrillation by a monophase impulse requires considerable discharge energy that increases injury of a myocardium. Since 2005, in view of accumulation of researches, the release of monophase defibrillators is stopped. The two-phase impulse is a bipolar impulse when current passes through a myocardium, and then changes the direction and passes once again. At the same time for the termination of circulation of excitement there are sufficient smaller values of energy that reduces the damaging action of current by a myocardium. Now unambiguously it is considered that the bi-phase defibrillation rather low categories (less than 200 J) is safe and more effective for stopping of fibrillation of ventricles, than the accruing single-phase categories.
In a hospital the countershock is used generally in three forms:
Carrying out the emergency defibrillation (at a cardiac standstill owing to fibrillation of ventricles and within the resuscitation actions);
Carrying out the emergency cardioversion (at emergence at the patient of zhizneugrozhayushchy tachyarrhythmias);
Carrying out planned cardioversion when EIT is used after attempts of medicamentous restoration of a rhythm at the prepared patient.
Safety rules when carrying out a countershock include the next moments:
It is impossible to hold both electrodes in one hand;
The charge can be gathered only when both electrodes are placed on the patient's breast;
It is necessary to avoid direct or indirect contact with the victim when carrying out the category;
The breast of the patient has to be dry;
It is necessary to remove oxygen (cylinders, a respiratory bag with an oxygen stream) from a defibrillation zone.