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In this Article

• What are implantable cardiac defibrillators (ICDs)?
• How does a normal heart function?
• How do abnormal heart rhythms decrease blood delivery by the heart?
• What is the cause of tachycardias?
• What are the symptoms of tachycardias?
• What are life-threatening tachycardias?
• What are the causes of ventricular tachycardia and ventricular fibrillation?
• How can ventricular tachycardia and fibrillation be treated and prevented?
• Who should receive an ICD?
• How are ICDs designed?
• How are ICDs implanted?
• What happens after implantation of an ICD?
• What are the complications of ICD implantation?
• What happens during a tachycardia episode after the placement of an ICD?
• Living with an ICD.
• What outside electrical sources are safe?
• What outside electrical sources can interfere with the ICD?
• What does the future hold for ICDs?
• Implantable Cardiac Defibrillators At A Glance
• Implantable Cardiac Defibrillator Index
• Find a local Cardiologist in your town

What are the causes of ventricular tachycardia and ventricular fibrillation?

Ventricular tachycardia and ventricular fibrillation are most commonly caused by heart attacks (acute myocardial infarctions) or scarring of the heart muscle from previous heart attacks. Less common causes of ventricular tachycardia and ventricular fibrillation include severe weakening of the heart muscles (cardiomyopathy), medication toxicity (such as digoxin toxicity), medication side effects, and blood electrolyte disturbances (such as a low potassium level). Ironically, some medications used in treating heart rhythm abnormalities can cause ventricular tachycardias.

How can ventricular tachycardia and fibrillation be treated and prevented?

Medications have traditionally been used in preventing ventricular tachycardia and fibrillation. Examples of these medications include Pronestyl and Cordarone and beta-blockers such as Tenormin and Inderal. Medicines, however, are not always successful in preventing tachycardias or in terminating tachycardias once they occur.

Once a life threatening tachycardia occurs, the most effective treatment is to administer mild electric shock(s) to the heart to terminate the tachycardia and reset the heart rhythm to normal.

If a patient is in cardiac arrest due to ventricular fibrillation, the treatment is the delivery of a strong electrical shock to the fibrillating heart without delay. Irreversible brain and other organ damages can occur within minutes if the normal heart rhythm is not restored. Most patients can potentially be saved if shocks are delivered quickly to convert the fibrillation to normal rhythm before irreversible brain damages occur.

The electrical shocks (mild and strong) that terminate ventricular tachycardia and fibrillation can be delivered by an external defibrillator (a portable unit with pads that deliver electrical shocks to the heart), or by an implantable cardiac defibrillator (ICD). External defibrillators, however, may not be readily available, and rescuers may not be able to administer effective CPR for long periods before paramedics arrive. Therefore, in patients known to be at risk of developing life-threatening tachycardias, ICDs can be implanted in their chests as a preventive measure to terminate tachycardias and fibrillation and avert cardiac arrest.