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Pacemakers, Defibrillators and Insertable Cardiac Monitoring Devices

Many types of small, implantable devices can be used to monitor and treat fast, slow and irregular heart rhythm problems. These devices include pacemakers, implantable cardioverter defibrillators (ICD) and new, advanced insertable heart monitoring devices used to help diagnose suspected heart rhythm disorders.

University of Chicago Medicine heart rhythm experts are leaders in the use of heart devices, and have many years of experience implanting these life-saving instruments in our state-of-the-art electrophysiology lab. Our physicians have access to the newest technology, and they are highly skilled at implanting the devices and selecting the right device for each patient's heart problem.

Device Implantation

Implantation of pacemakers and defibrillators involves the insertion of the device's leads (wires) into the heart through a catheter, or thin tube that is inserted into the body through a blood vessel. These leads are attached to the device that is inserted beneath the skin, usually just below the collarbone. When the heart rate is too slow, these devices send low-energy electrical current through the leads and to the heart muscle to pace the heart, stimulating the muscle to contract. Defibrillators also are capable of delivering a high energy shock to the heart when the heart rate is dangerously fast.

Unlike pacemakers or defibrillators, insertable cardiac monitoring devices do not have any wires. These devices are placed just below the skin of the chest.

Learn More About Heart Devices:


Pacemakers are small, electronic devices used to treat excessively slow heart rhythms (bradycardia). Pacemakers send signals to heart muscle that cause the muscle to contract at the correct pace, so that blood is pumped properly through the body. Today's advanced pacemakers adjust heart rates according to changes in the body's activity level. Thus, the pacemaker adjusts the heart's rate when the person is resting or exercising.

Different types of pacemakers exist. Single-chamber pacemakers send electrical impulses to one chamber (atrium or ventricle) of the heart, while dual-chamber pacemakers have wires placed in one atrium and one ventricle.

Different types of pacemakers exist. Single-chamber pacemakers send electrical impulses to one chamber (atrium or ventricle) of the heart, while dual-chamber pacemakers have wires placed in one atrium and one ventricle.
In this illustration, the dual-chamber pacemaker has a pacemaker lead placed in the right atrium and another lead placed in the right ventricle. These leads will stimulate the heart chambers to contract at the proper pace to move blood through the body.


Defibrillators, also called implantable cardioverter defibrillators (ICD), are devices for people who have life-threatening abnormal or fast heart rhythms or are determined to be at a high risk for cardiac arrest. ICDs continuously monitor heartbeats. When a dangerously fast heart rhythm occurs, the device is triggered to deliver a life-saving, high-energy electrical shock to restore proper heart rhythm.

ICDs may be appropriate for people who are at an increased risk of a cardiac arrest based on any of the following criteria:

  • People who have had heart attacks or have a cardiomyopathy and have congestive heart failure.
  • Diagnosis of ventricular tachycardia or ventricular fibrillation, or other disorders that cause abnormally fast or erratic heartbeats
  • Survivors of cardiac arrest
  • People with certain forms of inherited heart disease, such as hypertrophic cardiomyopathy, or a family history of sudden cardiac death

Biventricular Pacemakers (Cardiac Resynchronization Therapy) for Heart Failure

Normally, the left and right ventricles--the lower chambers of the heart--contract at the same time. Heart failure can disturb the heart's normal electrical pathway, causing uncoordinated, "asynchronous" pumping of the ventricles, further decreasing the heart's ability to properly pump blood. This defect of the heart's electrical system is called bundle branch block and is common among patients with congestive heart failure.

The biventricular pacemaker has three leads, one for the right atrium and right ventricle, and one that is placed in a vein on the surface of the left ventricle. The biventricular pacemaker stimulates the ventricles to contract together. This treatment is called cardiac resynchronization therapy.

At the University of Chicago, electrophysiologists work side-by-side with the heart failure care team to identify patients who may benefit from cardiac resynchronization therapy.

Insertable Cardiac Monitoring Devices

An insertable cardiac monitoring device is used to detect heart rhythm-related episodes of unexplained fainting (syncope) or palpitations.

An insertable cardiac monitoring device continuously monitors heart rhythm and records your heart's activity in the form of an electrocardiogram (ECG). When a fainting episode occurs, the device is triggered to save a record of the heart's activity before, during and after the spell. The device can be programmed to automatically record the episode or it can be prompted to save the ECG via a small hand-held device placed over the cardiac monitor. Our electrophysiologists can then read the ECG record to determine if an arrhythmia is present.

Other types of heart monitoring devices such as Holter monitors and event recorders are worn outside the body and are designed for more short-term use. An insertable cardiac monitoring device can be in place for up to three years, increasing the chances of documenting an infrequent fainting spell.

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