When discharging, it will definitely do harm to the human body, burn the skin and damage the myocardium. However, when saving people, you can ignore it. It is best to use conductive adhesive or physiological saline gauze under the electrode plate to reduce damage.
For different arrhythmia, the required voltage is different. If it is a single-phase defibrillator, ventricular fibrillation usually uses 300 joules, and the highest available is 360 joules. The power used for ventricular tachycardia, atrial fibrillation, atrial flutter and atrial tachycardia is relatively small (50-200 Joules), but if you are not sure, you would rather use a higher one and strive for a success. Otherwise, if you are unsuccessful, you must increase your strength and discharge again, which will delay the treatment and aggravate the injury. For biphasic defibrillators, use 150-200 Joules. If you are not sure, use 200 joules.
Electrical complex law generally does not talk about current, frequency and other indicators. I think current is determined by voltage and human impedance.
The principle is to make all myocardial cells release action potentials (depolarization) at the same time, and then automatically recombine the heart rhythm and restore the normal heart rhythm. If the normal pacing function of the heart itself is lost and the normal rhythm cannot be restored, a straight line will appear in the ECG, or arrhythmia will still appear before the attack.