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Implantable Defibrillator (ICD)

Also called: Implantable Cardioverter Defibrillator, Implantable Cardioverter, Automatic Defibrillator Implantation, Automatic Implantable Cardioverter Defibrillator, Single Chamber ICD, ICD, AICD, Dual Chamber ICD

- Summary
- About implantable defibrillators
- Conditions treated
- Function of the device
- About ICD implantation
- Potential risks
- Longevity and replacement
- Questions for your doctor

Reviewed By:
Abdou Elhendy, MD, PhD, FACC, FAHA
Robert I. Hamby, M.D., FACC, FACP
Suneet Mittal, M.D., FACC

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Conditions treated with ICDs

A series of landmark studies confirmed that ICDs significantly reduce the risk of sudden cardiac death due to abnormal heart rhythms (arrhythmias). In fact, some of the studies were ended earlier than scheduled due to the superior benefit shown by the ICD in comparison to drugs used alone.

Based on the results of these studies, an ICD may be recommended for patients who have experienced any of the following:

Previous heart attacks, with weakened functioning of the left ventricle. The performance of the left ventricle is expressed numerically as the left ventricular ejection fraction. It represents the proportion of blood in the heart that is pumped out with each beat. A normal range is between 55 percent and 75 percent. An ejection fraction below 40 percent has been shown to increase the risk of sudden cardiac death. ICDs may be recommended in patients with an ejection fraction of 30 percent of less. In heart attack survivors with reduced ejection fractions, it has been found that an ICD plus antiarrhythmic drugs significantly lowers the risk of sudden cardiac death, as compared to antiarrhythmics used alone.
History of ventricular tachycardia (VT) or ventricular fibrillation (VF) that does not respond to antiarrhythmic medications, or patients who cannot take antiarrhythmic medication for whatever reason.
Coronary artery disease. Patients with coronary artery disease may have an underlying arrhythmia. Up to 65 percent of cases of sudden cardiac death are caused by ventricular fibrillation that occurs in the presence of coronary artery disease. Studies have shown that, in patients with coronary artery disease who received an ICD, cholesterol-reducing drugs may have an anti-arrhythmic effect that can reduce the recurrence of ventricular tachycardia or ventricular fibrillation.
Cardiac arrest.
Heart failure, with or without coronary artery disease. Results from the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) suggest that ICD use can lower the risk of sudden cardiac death in patients with heart failure by more than 20 percent. These and other findings from the landmark study are causing a change in recommendations for the use of ICDs in patients with heart failure. Another study found that ICD use may result in fewer hospitalizations for heart failure patients. In the future, more heart failure patients are likely to benefit from ICD implantation.
Atrial fibrillation, when symptoms do not respond to treatment with medications. This relatively new use for ICDs is still being studied and would only be considered for the small percentage of atrial fibrillation patients who experience persistent symptoms.

Not every patient needs an ICD. ICDs are generally not necessary when an abnormal rhythm (arrhythmia):

Is an isolated occurrence with no underlying disease

Is caused by an electrolyte imbalance or drug overdose

Occurred within the first 48 hours after a heart attack

For patients having only an abnormally slow heartbeat (bradycardia), the preferred treatment is a pacemaker.