Although it weighs just about an ounce, a pacemaker contains a powerful battery, electronic circuits and computer memory that together generate electronic signals.
The signals, or pacing pulses, are carried along thin, insulated wires, or leads, to the heart muscle. The signals cause the heart muscle to begin the contractions that cause a heartbeat.
A pacemaker is implanted just below the collarbone in a procedure that takes about two hours. It is programmed to stimulate the heart at a pre-determined rate, and settings can be adjusted at any time. Routine evaluation, sometimes even via telephone, ensures the pacemaker is working properly and monitors battery life, which generally runs from five to ten years.
The most common reason for a pacemaker is a heartbeat that slows to an unhealthy rate, or bradycardia. A pacemaker resets the heart rate to an appropriate pace, ensuring adequate blood and oxygen are delivered to the brain and other parts of the body.
Pacemakers May Be Prescribed For A Number Of Conditions, Including:
- Atrial fibrillation
- Heart failure
Three basic types exist to serve different purposes:
Single-Chamber Pacemakers – In a single-chamber pacemaker, only one wire (pacing lead) is placed into a chamber of the heart. Sometimes it is the upper chamber, or atrium. Other times it is the lower chamber, or ventricle.
Dual-Chamber Pacemakers – In dual-chamber pacemakers, wires are placed in two chambers of the heart. One lead paces the atrium and one paces the ventricle. This approach more closely matches the natural pacing of the heart. This type of pacemaker can coordinate function between the atria and ventricles.
Rate-Responsive Pacemakers – These have sensors that automatically adjust to changes in a person’s physical activity.
Other devices – Some devices, such as implantable cardioverter defibrillators (ICDs), designed primarily for other purposes, can function as pacemakers in certain situations.
In the largest clinical trial of pacemakers conducted in the United States, researchers found that patients with sick sinus syndrome benefit from dualchamber pacemakers. They are less likely to develop atrial fibrillation or mild forms of heart failure compared to people who are treated with singlechamber pacemakers.
Full-contact sports can damage a pacemaker.
Magnetic Resonance Imaging (MRI) tests employ powerful magnets to create images. If you are scheduled for an MRI test, you should make certain your doctor knows you have a pacemaker.
Electronic security systems, such as those common in airports, can pose problems if exposure is prolonged. Passing through such systems, even several times, does not pose a threat. However, patients with pacemakers should avoid the “wand” used in some security checks. Microwave ovens, cellular phones and electric blankets do not, as myth might have it, affect pacemaker functioning.