What is a Defibrillator and How Does it Work?


The heart is one of the most powerful muscles in the body, and its ceaseless pumping is essential to sustaining life. If the hearts stops beating, blood stops flowing, the brain is deprived of its oxygen supply, and death can result in as little as 5 minutes. For someone who suffers a cardiac arrest, which is when the heart stops beating or has a life-threatening abnormal rhythm, emergency medical treatment is critical. While CPR (cardiopulmonary resuscitation) can help maintain the flow of oxygen to the brain, getting the heart restarted and beating normally again often requires defibrillation with an electric shock.

What is a Defibrillator?

Defibrillation, true to its name, actually stops fibrillation, which is the trembling that heart muscles adopt during cardiac arrest. A defibrillator does its work by using high voltage (about 200-1000 volts) to pass an electric current through the heart, so that it is jolted back into beating normally. The heart will get about 300 joules of electrical energy, which is about the same as what a 100 watt incandescent light bulb uses in 3 seconds.

How to Use a Defibrillator

The typical defibrillator that comes to mind is probably what you’ve seen on television medical shows, which is an electric supply unit and two metal electrodes that are known as paddles. These paddles are pressed firmly to the patient’s chest with insulating plastics handles so that the person administering the shock doesn’t get one as well. The most critical part of getting the current to flow to the heart is to place the paddles correctly. Put one paddle above and to the left of the heart and the other slightly below the heart and to the right. Another method involves placing one paddle on the front of the body and the other on the back. The electrodes must be close together to avoid skin burns, and they have to make good contact with the skin. To achieve this, a conducting gel is usually applied to the patient’s chest first.

In units designed for use by non-medical professionals in public places, there are sticky, self-adhesive electrode pads that are used instead of the paddles. Once the pads are applied, the operator should stand clear of the patient’s body to avoid an electric shock.

Defibrillators are often seen in public locations, and have become as common as fire extinguishers. This is because a defibrillator can be a life-saving device in a situation where time is of the essence. Those minutes ticking away while waiting for emergency medical personnel to arrive can be the minutes that make a difference between life and death.  If someone suffers cardiac arrest in public, even an untrained person can follow the simple instructions to provide defibrillation, dramatically increases someone’s chances for survival, cutting the risk of dying almost in half.

Types of Defibrillators

The types of defibrillators you are likely to see in public places are called automated external defibrillators (AEDs) and are designed to be used with little or no training. They have self-adhesive electrode pads and a built-in computer that provides automatic analytical data on the patient’s heart rhythm to know if the shock will make a difference and what level of shock you need. Defibrillation is of no use if the heart has completely stopped beating. More professional units used in hospitals and by emergency medical personnel have the paddles and gel and are called manual external defibrillators. With these, the medical personnel must determine if shock will work and what level to apply. Semi-automated defibrillators can be either automatic or manual. For patients who have irregular heart rhythms, an internal defibrillator can be planted into the chest like a pacemaker, or worn on the surface of the skin under the clothing to constantly monitor the heart rhythm and administer shock as needed.

For more information and to purchase either a used or new defibrillator, visit our defibrillator page on the Absolute Medical website.