implantable defibrillator

The automatic implantable defibrillator / cardioverter is commonly referred to as an AICD. It is a device that continuously monitors the heart rhythm.

If it detects an abnormally fast heart rhythm, it either electrically paces the heart very fast or delivers a small electrical shock to the heart to convert the heart rhythm back to normal. The rapid pacing is not felt by the patient but the electrical shock, if used, is felt as a strong jolt in the chest.

The device is normally used for the instantaneous treatment of immediately life threatening heart rhythms (i.e., ventricular tachycardia and ventricular fibrillation) that often can't wait for treatment until an ambulance arrives. Some people are now studying the use of these devices for the treatment of less dangerous heart rhythms as well, such as atrial fibrillation.

implantable defibrillator

The device is implanted in an operating room under deep sedation and is connected to the heart using special AIDC (Automatic internal defibrillator cardioverter) leads.

The procedure typically takes two to three hours and patients are discharged from the hospital on the following day. Older devices were implanted in the abdominal wall but the newer, smaller devices are implanted under the collarbone, similar to a standard pacemaker. Leads run from the device through a vein into the heart. These leads report the hearts electrical activity back to the device and deliver the electrical therapy, if needed. These devices can also act like a standard pacemaker and pace the heart if it ever beats too slowly.

Like a pacemaker, these devices must be continually monitored. A device placed on the skin overlying the device can find out about how the device has been programmed, determine the status of the battery, see if any pacing or shocks were given and the heart rhythm that was treated. The programming of the device can be modified as needed to best suit the patient's needs. Routine monitoring will detect a battery that is nearing the end of its lifespan long before it gives out. When this happens, the old device is removed and a new device is implanted. The leads are usually left in place.

If a patient feels a shock, they are generally advised to report it to their physician immediately. Feeling one shock does not necessarily mean that they have to be admitted to a hospital. The patient is generally brought into the office the next working day to interrogate the device. Patients experiencing multiple shocks are often admitted to the hospital, however.

These devices are not perfect. Sometimes they deliver therapy for non-life threatening fast heart rhythms. That is why it always important to interrogate the device after any shocks are felt by the patient. The programming or medications may then be altered based on what type of heart rhythm received the shock.


Arrhythmia: a malfunction in the hearts electrical system. Symptoms include palpitations (pounding, fluttering, thumping or racing feeling in the chest), shortness of breath, chest pain or heaviness, weakness, light-headedness, fainting and loss of consciousness

Atrium: the top chambers of the heart

Atrioventricular (AV) node: part of the hearts electrical pathway located at the hearts centre

Electrocardiogram or EKG: computerised recording of electrical activity of the heart

IV: intravenous needle and fluid drip

Sinoatrial (SA) node: the hearts natural pacemaker

Ventricles: the bottom chambers of the heart


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