How Does a Defibrillator Work?

Defibrillation is the process by which a “life-saving” electric shock is administered to the heart when it experiences erratic and irregular beating, also known as ventricular fibrillation (VF). The electrodes that are placed on the patient’s chest are a means of delivering an electrical shock in measured amounts to restore the heart’s normal function.


When the heart experiences VF, the nerve impulses from the brain are still received by the heart. The firing of the impulses is chaotic, the heart is unable to produce its rhythm and cannot pump the blood properly. Due to oxygen deprivation, the brain cells begin to die after 4-6 minutes.

The fluttering and twitching of the heart will continue until it no longer receives the electrical signals from the brain and it stops functioning completely unless the heart is shocked by means of an electric current into working properly again and this is where the AED plays a critical role.

How AEDs Work

AEDs or automatic external defibrillators are computerized equipment that analyse the patient’s heart rhythms and automatically administers the electric shock required for defibrillation. By using an AED within the first 3-5 minutes of a person having a sudden cardiac arrest, you can increase the patient’s survival rate significantly. AEDs are meant to be used by anyone who has little or no experience.

When the electrodes are placed on the patient’s chest, the built-in computer within the AED checks the rhythm of the patient’s heart and analyses the condition of the heart via the electrodes. The AED also analyses if the patient is suffering from ventricular fibrillation or ventricular tachycardia (VT) and then decides if the heart requires defibrillation in an attempt to restore normal rhythm or not. The AED machine will not provide an electric shock unless required and will only do so if a VF or VT is detected.

If the AED determines that an electric shock is required, then a recorded voice prompts the operator to press the button on the AED equipment that delivers the shock. The electric shock is delivered to the patient’s heart through the chest wall via the adhesive sticky electrode pads. The shock administered to the heart interrupts the irregular rhythm, stops all the activity of the heart and allows it to restart functioning normally. The audio prompts give instructions to the AED operator and guides them through the entire process.

In the case of a sudden cardiac arrest or SCA, CPR alone can’t save a patient’s life. The rate of survival with just CPR alone is around 5%. However, when CPR is administered along with a cardiac defibrillator in the first few minutes of an SCA, the patient’s survival chances increase significantly to more than 75%. Thus, having an AED at hand can help to avert SCA related emergencies and gives patients the best chance of survival until professional medical help arrives.


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