Implantable cardioverter-defibrillator

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Conduction system of the heart

Heart, front view

Heart, section through the middle

Normal heart rhythm

ICD; Defibrillation

An implantable cardioverter-defibrillator (ICD) is a device designed to quickly detect a life-threatening, rapid heartbeat coming from the bottom chamber of the heart. It tries to convert an abnormal rhythm back to normal by delivering an electrical shock to the heart. This action is called defibrillation.

An ICD can prevent sudden cardiac death.

An ICD is made of several parts:

• A pulse generator sends the powerful shock to the heart. It runs on batteries. The generator is implanted under the skin, usually on the upper left side of the chest.
• An electronic switchboard (circuit) tells the device when to "fire" the shock.
• Electrodes (wires) go through the veins of the heart and connect the heart to the rest of the device. The wires sense the heart beat and carry the shock to the heart muscle.

All ICDs have a built-in pacemaker. Pacing may be necessary to support the heart in some instances, for example, after a shock, or during a very slow heart beat. The pacemaker also allows the device to correct some rapid heartbeats by pacing even faster for a short period of time. Also, all of today's bi-ventricular pacemakers can work as an ICD.

The ICD continuously monitors the heartbeats to make sure they are normal. It only delivers a shock to the heart when it senses a life-threatening rhythm.

During the implantation of a pacemaker-type ICD, electrodes are inserted through the veins into the heart. The pulse generator is surgically buried under the skin of the chest, generally below the left collarbone.

Who needs an ICD?

An ICD can help prevent sudden death in those who have ventricular fibrillation (VF) or ventricular tachycardia (VT). Both of these conditions can make the heart stop pumping blood, which can cause you to suddenly pass out (lose consciousness) or even die. VF and VT are emergency situations that require quick medical treatment. Cardioversion (external defibrillation) can be used to shock the heart rhythm back to normal.