Implantable cardioverter-defibrillator
Key points
- An implantable cardioverter-defibrillator (ICD) is a device designed to quickly detect an abnormal heart rhythm (arrhythmia) and suppress it immediately.
- The ICD can convert the arrhythmia back to normal rhythm by delivering an electrical shock to the heart.
- This way the ICD can effectively prevent sudden death.
- Modern ICDs also include pacing capabilities so that the device can act as a pacemaker.
Alternative names
ICD
Information
An implantable cardioverter-defibrillator (ICD) is a device designed to quickly detect an abnormal heart rhythm (arrhythmia) and suppress it immediately. The ICD can convert the arrhythmia back to normal rhythm by delivering an electrical shock to the heart. This way the ICD can effectively prevent sudden death.
An ICD is a minicomputer, about the size of a small cell phone, that consists of:
- a pulse generator with batteries and a capacitor that can send a powerful shock to the heart
- an electronic logic circuit to tell the ICD when to discharge.
- lead electrodes placed in the heart (or, rarely, small electrodes placed under the skin), to sense the cardiac rhythm and deliver the shock to the heart muscle.
Modern ICDs also include pacing capabilities so that the device can act as a pacemaker. Pacing may be necessary to support the heart in some instances (for example, after a shock) or as a method to terminate certain arrhythmias.
The ICD permanently tests the heartbeats for regularity, but remains inactive until it senses a rhythm deemed life-threatening. Then, the ICD delivers a powerful electric shock to the heart. Each shock uses energy from the generator, transformed before the shock by a capacitor. The ICD batteries are designed to last 5 to 8 years.
During the implantation of an ICD, electrodes are inserted through the veins into the heart, and the pulse generator is surgically buried under the skin of the chest, generally below the left collarbone.
Who needs an ICD?
In some people, the heart either suddenly starts beating in a disorganized manner (ventricular fibrillation or VF), or it starts beating very rapidly (ventricular tachycardia or VT). Both VF and VT can make the heart stop pumping blood, leading the person to a sudden loss of consciousness or death. Arrhythmias like VT and VF require emergency treatment and are best treated in hospital coronary care units. In these units, VT and VF can be converted back to the normal rhythm by an electric shock given across the chest (external defibrillation).
Many episodes of VT or VF, however, occur outside hospitals and people without ICDs often die because defibrillation is not immediately available.
Candidates for ICDs are people at risk of sudden death, including:
- those who have survived a cardiac arrest due to VF not triggered by a recent heart attack
- those with life-threatening episodes of VT
- survivors of a heart attack
Written and revised by
Gerald Hurowitz, M.D.
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