Implantable Cardiac Defibrillators (ICDs)

Implantable cardioverter defibrillators (ICDs) treat heart arrhythmias occurring in the heart’s lower chambers, or ventricles, which can be life-threatening. All modern ICDs have a built-in pacemaker and are a bit smaller in size than a deck of cards.

Clinician and patient in University of Michigan Arrhythmia Clinic

ICDs provide immediate therapy for a life-threatening arrhythmia where the heart is beating too quickly by providing a jolt of electricity - a treatment called defibrillation. The treatment needs to be immediate because you can pass out or die within minutes if the heart is beating too fast and is unable to pump enough blood to the body. ICDs can also act as pacemakers if the heart is beating too slow.

ICDs continuously monitor heart rhythms and are programmed to deliver pacing impulses to restore the heart's natural rhythm, which can, in some cases, avoid the need for a shock. If necessary, however, the ICD will deliver a shock to the heart.

The device, which is smaller than a deck of cards, is implanted under the skin in a preformed pocket in the left pectoral area. The leads are inserted into the large subclavian vein and threaded into the heart and then secured within the right heart chambers.

Who Needs an ICD?

ICDs are usually implanted in people who have history of heart blockages and heart attack that have weakened their hearts, or in people with abnormal heart muscle tissue, such as appears enlarged or thickened hearts. Occasionally, ICDs are implanted in people who have an inherited heart defect that makes their heart beat abnormally. 

Types of ICDs

There are three types of ICDs:

  • Single chamber
  • Dual chamber
  • Biventricular devices

Single-chamber ICDs use a lead that is attached to the right ventricle. Dual-chamber ICDs use leads that are attached to the right atrium and the right ventricle.

Biventricular ICDs

The biventricular ICD is to provide cardiac resynchronization therapy for patients who have had heart failure. Traditional pacemakers treat slow heart rates by regulating the right atrium and right ventricle to maintain a good heart rate and keep the atrium and ventricle working together in what is called AV synchrony. With a biventricular ICD, there is a third lead to the left ventricle as well to help the left ventricle beat in a synchrony with the right ventricle.

Biventricular ICDs can improve symptoms of heart failure in about half of patients who are still symptomatic while taking medication for heart failure.

See the ICD FAQ page for more information.

Patient Resources

Heart Rhythm Disorders Information Guide

Make an Appointment

The Arrhythmia Program at the University of Michigan has been a national and international leader in the treatment of arrhythmias for more than 30 years. To schedule an appointment to discuss your heart arrhythmia or other cardiovascular condition, call us at 888-287-1082, email us at Visit our Make an Appointment page for more information about what to expect when you call us.