Implantable Cardiac Defibrillators (ICDs)

Implantable cardioverter defibrillators (ICDs) are devices used to treat patients with heart arrhythmias that occur in the heart’s lower chambers, or ventricles, which can be life threatening.

Clinician and patient in University of Michigan Arrhythmia Clinic

ICDs are typically implanted in patients who have a weakened heart due to a history of heart blockages and/or heart attacks, or in those with heart muscle tissue that is enlarged or thickened. Occasionally, ICDs are implanted in patients who have an inherited heart defect that makes their heart beat abnormally.

How Does it Work?

An ICD provides immediate therapy for a life-threatening arrhythmia where the heart is beating too quickly by providing a shock, or jolt of electricity — a treatment called defibrillation. The treatment needs to be immediate to prevent a person from passing out or dying if the heart is beating too fast and is unable to pump enough blood to the body. Patients describe the shock as a pain in either the back or chest area. The pain differs with everyone and lasts for a very short amount of time.

Most ICDs can also act as pacemakers if the heart is beating too slowly. In this role, the ICD continuously monitors heart rhythms and is programmed to deliver pacing pulses (which cannot be felt) to restore the heart's natural rhythm. The goal of these pacing pulses is to avoid the need for a shock. However, the ICD will deliver a shock to the heart if the heart’s natural rhythm is not restored during the pacing pulses.

The device, which is smaller than a deck of cards, is implanted under the skin in a pre-formed pocket in the left chest area. Leads (wires) are either inserted into the large subclavian vein and threaded into the heart (tranvenous) or placed under the skin above the heart (subcutaneous).

Types of ICDs

There are four types of ICDs:

  • Single chamber
  • Dual chamber
  • Biventricular
  • Subcutaneous

Single-chamber ICDs use a lead (wire) that is attached to the right ventricle to deliver energy, if needed. Dual-chamber ICDs use leads that are attached to the right atrium and the right ventricle.

The biventricular ICD provides cardiac resynchronization therapy for patients who have had heart failure. This type of ICD has leads attached to the right atrium, the right ventricle and the left ventricle. Biventricular ICDs can improve symptoms of heart failure in about two-thirds of patients who remain symptomatic while taking medication for heart failure.

Subcutaneous ICDs work by monitoring the heart rhythm through wires placed just under the skin above the heart. The advantage of a subcutaneous ICD (also called an “S-ICD”) is that there are no wires in the body’s circulatory system, so the risk of the most serious infections is decreased. One disadvantage is that S-ICDs cannot pace the heart out of a dangerous rhythm, and are only able to treat arrhythmias with shocks.

See the ICD FAQ page for more information.

Patient Resources

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 CVCCallCtr@med.umich.edu. Visit our Make an Appointment page for more information about what to expect when you call us.