How Does an Implantable Cardioverter Defibrillator Work?

An implantable cardioverter defibrillator (ICD) has wires with electrodes on the ends that connect to one or more of your heart's chambers. These wires carry the electrical signals from your heart to a computer in the ICD. The computer monitors your heart rhythm.

If the ICD detects an irregular rhythm, it sends low-energy electrical pulses to prompt your heart to beat at a normal rate. If the low-energy pulses restore your heart’s normal rhythm, you may avoid the high-energy pulses or shocks of the defibrillator (which can be painful).

Single-chamber ICDs have a wire that connects to either the right atrium or right ventricle. The wire senses electrical activity and corrects faulty electrical signaling within that chamber.

Dual-chamber ICDs have wires that connect to both an atrium and a ventricle. These ICDs provide low-energy pulses to either or both chambers. Some dual-chamber ICDs have three wires. They connect to an atrium and both ventricles.

The wires on an ICD connect to a small metal box implanted in your chest or abdomen. The box contains a battery, pulse generator, and computer. When the computer detects irregular heartbeats, it triggers the ICD's pulse generator to send electrical pulses. Wires carry these pulses to the heart.

The ICD also can record the heart's electrical activity and heart rhythms. The recordings can help your doctor fine-tune the programming of your ICD so it works better to correct irregular heartbeats.

The type of ICD you get is based on your heart's pumping abilities, structural defects, and the type of irregular heartbeats you've had. Whichever type of ICD you get, it will be programmed to respond to the type of irregular heartbeat you're most likely to have.