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Implantable cardioverter defibrillator (ICD)

An implantable cardioverter defibrillator, or ICD, is a matchbox sized device similar to a pacemaker, and is fitted under the collar bone to manage abnormal heart rhythms or arrhythmias.

The ICD constantly monitors heart rate and rhythm. When it detects a very fast, abnormal heart rhythm, it delivers energy to the heart muscle. This causes the heart to beat in a normal rhythm again.

The ICD has two parts: the electrode leads and a pulse generator. The leads monitor the heart rhythm and deliver energy used for pacing and defibrillation. The generator houses the battery and a tiny computer. Energy is stored in the battery until it is needed. The computer receives information from the leads to determine what rhythm is occurring.

There are different types of ICDs, including:

  • Single chamber ICD. A lead is attached in the right ventricle. If needed, energy is delivered to the ventricle to help it contract normally.
  • Dual chamber ICD. Leads are attached in the right atrium and the right ventricle. Energy is delivered first to the right atrium and then to the right ventricle, helping your heart to beat in a normal sequence.
  • Biventricular ICD. Leads are attached in the right atrium, the right ventricle and the left ventricle. This technique helps the heart beat in a more balanced way and is specifically used for patients with heart failure.

Your cardiologist will determine which type of ICD is best for you.

How does an ICD work?

The ICD monitors the heart rhythm, identifies abnormal heart rhythms, and determines the appropriate therapy to return your heartbeat to a normal rhythm. Your doctor programs the ICD to include one or all of the following functions:

  • Anti-tachycardia pacing (ATP). When the heart beats too fast, a series of small electrical impulses are delivered to the heart muscle to restore a normal heart rate and rhythm.
  • Cardioversion. A low energy shock is delivered at the same time as your heartbeat to restore a normal heart rhythm.
  • Defibrillation. When the heart is beating dangerously fast, a high-energy shock is delivered to the heart muscle to restore a normal rhythm.
  • Bradycardia pacing. When the heart beats too slow, small electrical impulses stimulate the heart muscle to maintain a suitable heart rate.

Who is a candidate for an ICD?

ICDs are used for:

  • People who have had an episode of cardiac arrest or ventricular fibrillation.
  • People who have had a heart attack and are at high risk of cardiac arrest.
  • People who have hypertrophic cardiomyopathy and are at high risk of cardiac arrest.
  • People who have had at least one episode of ventricular tachycardia, an abnormal heart rhythm.

How should I prepare for the procedure?

  • Ask your doctor what medications you are allowed to take. Your doctor may ask you to stop taking certain medications before the procedure. You will receive specific instructions.
  • If you have diabetes, ask your doctor how you should adjust your diabetes medications.
  • Do not eat or drink anything after midnight the evening before the procedure. If you must take medications, drink only with a sip of water.
  • When you arrive at the hospital, wear comfortable clothes. You will change into a hospital gown for the procedure. Leave all jewellery and valuables at home.
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