By Richard P. Abben, M.D.
Director,
Arrhythmia Center
Cardiocascular Institute of the South

Your heartbeat is controlled by the heart's own bioelectrical triggering system. When that system ceases to work properly, the solution may be a pacemaker.

The pacemaker has two parts -- a battery-powered generator and the wires that connect it to the heart. The silver-dollar-size generator, which has an effective life of seven to 12 years, is implanted just beneath the skin below the collarbone. The leads are threaded into position through veins leading back to the heart. The entire implantation procedure requires only a local anesthetic, and takes about an hour.

Most patients with pacemakers suffer from a condition in which the heart beats too slowly -- bradyarrhythmia is the medical term. This is most commonly a result of deterioration in the heart's own pacing system in elderly patients, though high blood pressure, coronary artery disease or scarring from a heart attack can also cause bradyarrhythmias.

The most commonly installed pacing device is a demand pacemaker. It monitors the heart's activity and takes control only when the heart rate falls below a programmed minimum -- usually 60 beats per minute.

Other conditions which require pacemakers include heart block -- in which the heart stops beating altogether for several seconds-- and tachyarrhythmia-- an overly rapid heartbeat.

A more sophisticated type of pacemaker actually monitors a number of physical changes in the body which signal an increase or decrease in activity. If the heart's own pacing system fails to respond properly, these rate-responsive pacemakers slowly raise or lower the heartbeat to the appropriate level -- from 60 to perhaps 150 beats per minute.

If the patient's condition dictates reprogramming the implanted generator, the cardiologist signals the changes to its tiny on-board computer with an electromagnetic signaling device placed on the surface of the skin above the pacemaker.

Probably the most commonly encountered public references to pacemakers are the warning signs posted in convenience stores and snack bars advising pacemaker patients that a microwave oven is installed. That warning is no longer necessary. Modern pacemakers are shielded from stray electromagnetic forces and have a backup mode that takes over if a really strong electromagnetic field does disrupt the main circuit's programming.

&copy 1995 Cardiocascular Institute of the South

For further information, call Jane Arnette, Cardiocascular Institute of the South/Houma, 1-800-425-2565, or Jim Keyser at 1-800-848-2715. E-mail questions or comments to: jakeyser@cardio.com.

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