What Is an Automatic Internal Cardiac Defibrillator?

An ICD (automatic internal cardiac defibrillator or internal cardioverter defibrillator) is a mechanical device that monitors the heart rate and rhythm. If it detects an abnormal heart rhythm, it shocks the heart to cause it to beat normally again. Leads attached to the device are placed in the atria and/or ventricle of the patient, and the device is planted just above the breast muscle.

Purpose

• The purpose of an ICD is to keep heart patients healthy and to prolong life. The devices often are implanted in patients who have had an episode of cardiac arrest, people who have had a heart attack and are in danger of sudden death, or people who have abnormal, dangerous heart rhythms.

Types

• There are three types of ICDs: a single chamber ICD, a dual chamber ICD and a biventricular ICD. The type of ICD is chosen with the needs of the patient in mind. Those with more severe heart disease or failure require a biventricular ICD, while other heart problems require the other types.

Mechanics

• The two main parts of an internal cardiac defibrillator are the leads and a pulse generator. The leads monitor the heart rhythm and deliver energy used for pacing and defibrillation. The generator holds a computer and the battery. Energy is stored in the battery until it is needed; the computer gets information from the leads in order to monitor the rhythm.

Implantation Procedure

• To implant the ICD, a small incision is made under the collarbone and the lead is placed into a vein, where it is guided inside the heart chamber. A generator then is placed under the skin in the upper chest and attached to the leads. In patients with special heart problems, an ICD might need to be implanted outside the heart. In this procedure, the chest is opened and the ICD is sewn to the heart.

Function

• An ICD monitors heart information, and it also is capable of performing four main functions including anti-tachycardia pacing (slows the heart), cardioversion (restores normal heart rhythm), defibrillation (slows heart with a shock) or bradycardia pacing (speeds up the heart).