What Is a Pacemaker?

A pacemaker is a small device that's placed under the skin of your chest or abdomen to help control abnormal heart rhythms. This device uses electrical pulses to prompt the heart to beat at a normal rate.

Pacemakers are used to treat heart rhythms that are too slow, fast, or irregular. These abnormal heart rhythms are called arrhythmias (ah-RITH-me-ahs). Pacemakers can relieve some symptoms related to arrhythmias, such as fatigue (tiredness) and fainting. A pacemaker can help a person who has an abnormal heart rhythm resume a more active lifestyle.

The Heart's Electrical System

Your heart has its own internal electrical system that controls the speed and rhythm of your heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal causes the heart to contract in an organized manner and pump blood.

Electrical signals normally begin in a group of cells called the sinus node. As these signals spread from the top to the bottom of the heart, they coordinate the timing of heart cell activity. First, the two upper chambers of the heart, called atria (AY-tree-uh), contract. This contraction squeezes blood into the lower chambers of the heart, which are called ventricles (VEN-trih-kuls). The ventricles then contract and send blood to the rest of the body. The combined contraction of the atria and ventricles is a heartbeat.

For more information about the heart's electrical system and how a healthy heart works, see the Diseases and Conditions Index article on How the Heart Works.

Overview

Faulty electrical signaling in the heart causes arrhythmias. A pacemaker uses low-energy electrical pulses to correct faulty electrical signaling. Pacemakers can:

• Speed up a slow heartbeat
• Help end an abnormal and fast rhythm (only in implantable cardioverter defibrillator/pacemaker combination devices)
• Make sure the ventricles contract normally if the atria are quivering instead of beating in a normal rhythm (a condition called atrial fibrillation)
• Coordinate the electrical signaling between the upper and lower chambers of the heart
• Coordinate the electrical signaling between the ventricles (cardiac resynchronization therapy used in heart failure)

Pacemakers also can monitor and record your heart's electrical activity and the rhythm of your heartbeat. Newer pacemakers can monitor your blood temperature, breathing rate, and other factors and adjust your heart rate to changes in your activity.

Pacemakers can be temporary or permanent. Temporary pacemakers are used to treat temporary heartbeat problems, such as a slow heartbeat due to heart attack, heart surgery, or an overdose of medicine. Temporary pacemakers are used in emergencies until a permanent pacemaker can be implanted or until the temporary condition goes away. A person with a temporary pacemaker will stay in the hospital as long as the pacemaker is in place.

In this article, "pacemakers" refers to permanent devices, unless stated otherwise.

Doctors also treat arrhythmias with another device called an implantable cardioverter defibrillator (ICD). An ICD is like a pacemaker in some ways, but it can use higher energy electrical pulses to treat certain dangerous types of arrhythmia. For more information on ICDs, see the Diseases and Conditions Index article on Implantable Cardioverter Defibrillator.

May 2008