When the heart's own natural pacemaker, the sinus node, malfunctions or stops working, an artificial pacemaker can be implanted to generate regular impulses.
Pacemakers rest just under the collarbone to stimulate the heart when the heartbeat slows to an unhealthy rate in a condition called bradycardia.
Pacemakers may also be recommended for certain patients with atrial fibrillation, heart failure or syncope, a condition in which patients faint when their heart rhythm becomes very slow.
The pacemaker resets the heart rate to an appropriate pace, ensuring adequate blood and oxygen flow to the brain and other parts of the body. Although it only weighs about an ounce, a pacemaker contains a long-lasting power supply, electronic circuits and computer memory that work together to generate electronic signals.
The signals, or pacing pulses, are carried along thin, insulated wires (or "leads") to the heart muscle. These signals stimulate the heart muscle at a pre-determined rate, which trigger the contractions that cause a heartbeat.
With single-chamber pacemakers, only one wire is placed into a chamber of the heart. In dual-chamber pacemakers, one "lead" wire paces the atrium and another paces the ventricle. Rate-responsive pacemakers have sensors that automatically adjust to changes in a person's physical activity.
Routine evaluation ensures the pacemaker is working properly and monitors battery life, which generally runs from five to 10 years.