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Heart Disease Health Center

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Abnormal Heart Rhythms and Implantable Cardioverter Defibrillators (ICD)

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Treatment for abnormal heart rhythms is possible with an ICD, or implantable cardioverter defibrillator. An ICD is an electronic device that constantly monitors your 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 lead(s) and a pulse generator. The lead(s) are made up of wires and sensors that monitor the heart rhythm and deliver energy used for pacing and/or defibrillation (see below for definitions). 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 how the heart is beating.

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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 restore a normal heart rhythm.
  • Dual-chamber ICD. Leads are attached in the right atrium and the right ventricle. Energy can be delivered to the right atrium and then to the right ventricle, helping your heart to be paced in a normal sequence.
  • Biventricular ICD. Leads are attached in the right atrium, the right ventricle and the coronary sinus, adjacent to the left ventricle. This technique helps the heart beat in a more efficient way and is specifically used for patients with heart failure.

Your doctor 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:

  • Antitachycardia 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 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.

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