What are the Different Types of Defibrillator?

Sarah R. LaVergne

A defibrillator is used to shock a beating heart into momentarily stopping when the heart's rhythm is dangerously erratic, whether it's too fast or too slow. The momentary stoppage allows the heart to regroup and try to start beating at a normal pace. There are many types of defibrillators — including monophasic, biphasic and internal — all of which function by sending an electrical current to the heart.

A defibrillator.
A defibrillator.

The first two types are known as external defibrillators, and these are used on the exterior of the patient’s chest. Pads are placed on the chest and a button is pushed to send an electrical current to the heart. The type of external defibrillator determines the type of current sent to the heart.

Defibrillators are used to restart a heart or to restore a regular heartbeat via an electric shock to the heart.
Defibrillators are used to restart a heart or to restore a regular heartbeat via an electric shock to the heart.

A monophasic defibrillator sends out a single electrical pulse. This shot of electricity goes from one pad to the other with the heart in between. The electrical energy meets in the middle and shocks the heart. A monophasic defibrillator needs high electricity levels to function correctly. The charge is typically started at 200 joules and increased to 300 joules; if necessary, the highest level is 360 joules.

The second type of external device is biphasic, and it sends out two electrical currents. A current first travels from one pad to the other. The electricity then reverses direction and returns a current to the first pad. This enables the biphasic device to use less electricity than the monophasic variety. The biphasic defibrillator also is able to adjust to the patient's body type.

The third type of defibrillator is the internal or implantable variety, which is surgically placed in the chest of a patient. The electrode wires are inserted through the veins into the right chamber of the heart. An internal defibrillator monitors the heartbeat for any irregularities. If the heart skips a beat, the defibrillator sends a current of energy directly to the heart through the electrodes. Internal defibrillators run on battery power instead of electricity.

Defibrillators were created to help doctors and other medical professionals save lives. A fourth type of defibrillator, the automated external defibrillator (AED), can help ordinary people do the same in emergency situations. AEDs are portable and can be found in many public areas and some private homes. Once a person has placed the pads on a potential patient, an AED can check the person's heart rate, determine whether a shock is required, and then coach the user through the proper steps to administer the shock. While it is preferable that a person be trained in the use of an AED, the machines are sufficiently automated that training isn't absolutely necessary.

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