Pacemakers and ICDs: A Patient Guide

These electronic medical devices monitor heart rhythm and deliver appropriate electrical therapy when certain arrhythmias occur. Pacemakers and ICDs can be effective in extending and improving the lives of heart patients. Millions of people are affected by arrhythmias, which contribute to about 500,000 deaths each year in the US.

What are artificial pacemakers?

An artificial pacemaker stimulates a programmed and appropriate heartbeat in patients who have a slow heart rate. The pacer is a device that is made up of a battery-powered generator that sends signals to the heart through wires that are connected to the heart . The pacer senses heartbeats and fires a stimulus back to the heart if the beats that it senses do not come at the appropriate time. A pacemaker therefore detects heartbeats that are too slow or irregular and provides electrical signals that tell the heart to beat at a proper rate by delivering signals to the appropriate chambers of the heart.

Pacemakers are surgically implanted beneath the skin, usually just below the collarbone. Many pacemakers are programmed to lie dormant for as long as the heart is beating at a steady rate above 50 to 70 pulses per minute. Should the rate slow beyond a certain rate, the pacer will fire and raise the heart rate.

What is an implantable cardioverter defibrillator (ICD)?

Somewhat more complex than pacemakers, ICDs are devices that monitor the heart constantly, but only initiate an electrical signal when it detects a prespecified rhythmic abnormality that is dangerous. ICDs can function as pacemakers for slow heart rates, but may also deliver high-energy electrical therapy for certain fast heart rates, called defibrillation shocks The increases in heart rate that are normal with exercise should not cause firing). Surgically implanted like a pacemaker, an ICD is a miniature (but internal) version of the shock paddles used by paramedics and emergency room doctors.

Who needs an artificial pacemaker?

A natural pacemaker in the heart called the sinus node controls normal heartbeat. An electrical signal is generated by the sinus node, a group of special cells in one of the upper chambers of the heart, called the atria. The signal spreads through the heart to the lower chambers, called the ventricles, and causes the heart to beat.

A pacemaker is needed when the function of the sinus node becomes too slow from age, heart disease, or heart medications. Another leading cause for pacemaker implantation is heart block-the failure of the electrical signal to reach the main pumping chambers of the heart, which in turn causes a slow heart rate.

When the heart beats too slowly, the brain and body may not get enough blood flow, leading to fainting, dizziness, easy fatigability, shortness of breath, and low tolerance for exercise and physical activity. Extreme slowing or complete stopping of the heartbeat can be fatal.

Who needs an ICD?

ICDs have been proven to prolong survival in some patients with dangerous heart rhythms, usually those who have damaged hearts. Patients may be survivors of cardiac arrest caused by ventricular tachycardia or fibrillation (VT or VF), heart rhythm disorders that originate in the ventricles . VT or VF patients may feel faint or dizzy, or even pass out. During VT or VF, the heart does not pump blood adequately because rapid contractions prevent it from filling adequately with blood between beats. VT or VF can be fatal, if not properly treated.

In some cases, depending upon the underlying cardiac status atrial fibrillation (AF) can be cause significant patient instability. During atrial fibrillation, electrical signals move chaotically through the atria, and if the rapid stimuli pass to the ventricles and result in loss of consciousness. If left untreated, it may result in sudden cardiac death.

An ICD can deliver several types of therapies. These therapies include defibrillation, which delivers a brief, high-energy electric shock, and cardioversion, which consists of synchronized shock impulses that may progress from low-energy to high-energy levels, depending on what is needed to stop the rapid rhythm.

An ICD can act like a pacemaker by stimulating the heart if the rate is too slow. This requires little energy, so it is not felt. If an ICD detects a rapid beat, it can emit a series of pulses, which will be perceived as a fluttering in the chest. If this fails, the ICD can deliver one or more mild shocks, which may be felt as thumps to restore normal rhythm.

If the ICD detects any rhythms that are programmed to be considered more dangerous it will provide a high-energy shock to get control of the rhythm. The defibrillating shock is a strong one that feels like a kick in the chest. It may also save a life.


An artificial pacemaker or ICD is implanted by a minor surgical procedure performed under local anesthesia. The surgery usually takes 1 to 2 hours and the risk of complications is approximately 1 to 2 percent. A pacemaker, about as large as 3 silver dollars, is placed beneath the skin just below the right or left collarbone. The wire or wires are threaded through a large vein into the heart. Using an X-ray, a physician attaches the electrodes at the end of the wires to the inner wall of the heart. The other end of the wire is attached to the device.

An ICD is larger than a pacemaker-about as big as a pager-and is implanted in a similar manner.

Pacemaker and ICD precautions

These devices generally will not prevent you from performing everyday activities, but certain precautions should be considered. Remember to tell your doctor and dentist that you have the device before having any test or procedure. It is also wise to carry a medical ID card in your wallet because medical equipment that uses electromagnetic and radio wave technology may interfere with how your device performs. For example, magnetic resonance imaging (MRI), which uses a magnet to produce images of organs, may interrupt your device's operation. At the current time MRI is not usually considered for patients who have a pacemaker or ICD.

Other medical equipment used to dissolve kidney stones, treat irregular heart rhythms, treat acute or chronic pain, and deliver radiation for treatment of cancerous tumors may interfere with your device's performance or require reprogramming of the device.

Home appliances do not pose a threat to your device's operations, but large motors, high-voltage and radar machinery, such as transmitters and arc welding equipment, could temporarily affect your device.


Reiffel, James A., Dizon, Jose. The Implantable Cardioverter-Defibrillator-Patient Perspective. Circulation. 2002;105:1022-1024.

Wood, Mark A., Ellenbogen, Kenneth A. Cardiac Pacemakers From the Patient's Perspective. Circulation. 2002;105:2136-2138.

Baptist Health. Implantable Cardioverter Defibrillator (ICD).

American Academy of Family Physicians. The Implantable Cardioverter-Defibrillator.

American Heart Association. Pacemakers.

Last Updated: April 2008