ICDs and Pacemakers FAQ

There are different types of ICDs, and your doctor will determine which is best for your condition. This list of FAQs will help you understand what an ICD is, why you might need an ICD, and how ICDs work for your specific condition and individual needs. Talk with your doctor to learn more about the ICD that is best for you.

What is an implantable cardiac defibrillator (ICD)?

An implantable cardiac defibrillator is an electric device that constantly monitors your heart rhythm. When it detects a fast or abnormal beat (ventricular tachycardia), it is programmed to deliver energy to the heart muscle to convert the heartbeat back to its normal rhythm.

Why do I need an ICD?

ICDs are used to prevent sudden death in individuals who are at risk for life‐threatening arrhythmias, or irregular heart beats. According to the American Heart Association, studies have shown that ICDs play a role in preventing cardiac arrest in patients with certain risk factors or with known, sustained ventricular tachycardia (unusually fast heartbeat) or fibrillation (quivering or irregular heartbeat).

How does an ICD work?

The ICD monitors your heart rhythm, identifies abnormal rhythms and determines the correct therapy that will return your heart beat to its normal state.

The ICD is implanted in the upper chest and the device is connected to the heart with thin, flexible wires. If the ICD and leads detect an abnormal heart rhythm – either beating chaotically or too fast – the device will deliver an electric shock through the leads directly to the heart to restore a normal heartbeat.

What is a pacemaker?

Pacemakers are used to treat abnormally slow heartbeats (bradycardia). A pacemaker is a device that sends small electrical impulses to the heart muscle to maintain a normal rate or stimulate the lower chambers of the heart to beat. A pacemaker may also be used to treat fainting spells (called syncope), congestive heart failure and hypertrophic cardiomyopathy.

How does a pacemaker work?

A pacemaker monitors the heart by reading signals sent back to the pulse generator that travels through the leads connected to the ventricle (lower chamber of the heart) or atrium (upper chamber of the heart). When it detects too slow of a heartbeat, the generator (pacemaker) delivers impulses of electrical energy that pace the heart at a normal rate (or programmed rate), to maintain normal function.

Why do patients need magnetic resonance imaging (MRI) scans?

MRIs use high‐energy magnetic fields and radio waves to create detailed images of the body’s organs and structures. MRI images clearly depict body parts that are not seen as well with other imaging options such as X‐ray, CT or ultrasound scans. MRI is especially helpful for diagnosing problems with joints, cartilage, ligaments and tendons, as well as problems with eyes, ears, heart and circulatory system.

Why were ICD patients previously denied MRI scans?

The strong magnetic forces applied during MRI scans may negatively affect both the leads and the ICD device. It is known that some metals respond to the strong magnetic fields and radio frequency energy produced by MRI scans by absorbing and conducting heat. A lead incapable of dissipating all of this heat could cause damage to the heart or become ineffective at transmitting the heart signals that the device depends on. Once you move away from the interference the device likely resumes its normal function.