Because a defibrillator can control the energy of the shock, releasing an electric current through the heart in a very short period of time, so that all the back of the cardiac muscle cells are able to answer enough to produce "excitement" at the same time in an instant, the defibrillator will not electrocute people.
Defibrillation requires energy, and when defibrillating, the appropriate energy is selected to generate sufficient current through the myocardium. If the energy and current are too low, the shock will not terminate the arrhythmia. If the energy and current are too high, functional and morphological damage can result. In adults there is no clear relationship between body size and the energy required for defibrillation, and transthoracic impedance does not play an important role.
Expanded information:
Principle of operation
Cardiac defibrillation resuscitation acts on the heart with a single transient high-energy pulse, generally of 4 to 10 ms duration, with an electrical energy in the range of 40 to 400 J (joules). The device used to defibrillate the heart with an electric shock is called a defibrillator, and it accomplishes the shock resuscitation, or defibrillation.
When patients experience severe tachyarrhythmias, such as atrial flutter, atrial fibrillation, and supraventricular or ventricular tachycardia, they often result in varying degrees of hemodynamic impairment.
Particularly when patients with ventricular fibrillation, due to the ventricle without the overall contraction ability, the heart ejection and blood circulation termination, if not timely rescue, often resulting in the death of the patient due to the lack of oxygen in the brain for too long. If a defibrillator is used to control a certain amount of energy current through the heart, it can eliminate certain arrhythmias and can restore the heart rhythm to normal, thus enabling patients with the above heart diseases to be rescued and treated.
The original defibrillator is the use of industrial alternating current to defibrillate directly, this defibrillator will often be electrocuted and casualties, therefore, at present, in addition to cardiac surgical procedures, there is also the use of alternating current for in vivo defibrillation (ventricular fibrillation), generally use direct current defibrillation.