What is the operating principle of a defibrillator?

• A. A current of 200 mA can reset the heart.
• B. It monitors heart rate without stimulation.
• C. It cools the chest to reduce risk.
• D. It compresses the chest to restart circulation.

Answer: (A)

Defibrillators reset the heart by delivering a brief, strong electrical impulse that depolarizes a large portion of the heart muscle. This momentary disruption of the heart’s chaotic electrical activity (such as in ventricular fibrillation) allows the heart’s natural pacemaker to regain control and restore a normal rhythm. The essential idea is the electrical shock that “resets” the heart, rather than simply monitoring or performing other actions. While the exact current or energy delivered can vary with body impedance and device settings, the principle remains: an electrical impulse is used to depolarize enough tissue to reestablish organized rhythm. Cooling the chest or performing chest compressions are separate resuscitation methods, not the operating mechanism of how a defibrillator works.