User manual



3. Principles and applications of defibrillators



Theoreticalintroduction

 Defibrillation is used to eliminate fibrillations (cardiac arrhythmias, 340-600

pulses/min) of the cardiac muscles by means of artificially created electrical discharge (pulse)

of a great energy. Application of defibrillation is most common in ventricular fibrillation,

ventricular flutter or in sustained polymorphous ventricular tachycardia (longer than 30 s).

Defibrillation causes depolarization of all the cells in the heart, which allows for restoring

regular heart rhythm. Defibrillation’s effectiveness is very much influenced by the size of the

passing current (single units to tens of Amperes). The size of the current depends on the

impedance size of the patient’s tissue (tens to hundreds of Ohms) and on the transition

resistance of the electrodes, as well as on the shape of the defibrillation pulse. Greater

impedance of the patient reduces the value of the passing current, which is compensated by

the prolongation of the defibrillation pulse’s duration (single units to tens of milliseconds).

The surface below the defibrillation pulse’s curve thus remains preserved, being the energy of

this pulse.

In external defibrillators, the amount of energy of the defibrillation pulse is adjustable

within the scope of 50-400 Joules [J]; in implantable defibrillators (ICD - Implantable

Cardioverter-Defibrillator), the size of the defibrillation pulse varies between 1-50 J (30 J),

depending on the defibrillator’s type and manufacturer. Defibrillators currently manufactured

use several types of defibrillation pulses.

Fig. 3.1: Demonstration of monophasic depolarizing pulses (from the left: trapezoidal,

damped, damped with delay).

Depending on the number of pulse stages, we divide the defibrillation pulse to

monophasic pulse (Fig. 3.1), when direct current is passed onto the patient in one direction