The High Tech Heart: What to Expect from a Pacemaker
The heart has a "natural
pacemaker" - the sinoatrial (SA) or sinus node - that
produces bioelectrical impulses that cause the heart to beat regularly. If there
is a problem with the SA node, the heartbeat can become too slow (bradycardia),
too fast (tachycardia) or irregular (arrhythmia). When this occurs an artificial
pacemaker may be considered to correct the problem.
An artificial pacemaker
replaces the natural pacemaker or overcomes a blockage of the heart's electrical
pathways. Some artificial pacemakers are permanent, installed under the skin
during surgery, and some are temporary, applied externally. The implantation
procedure requires only a local anesthetic, and takes about an hour.
A pacemaker consists of a
battery-powered generator and the wires that connect it to the heart. The
generator, which is about the size of a silver dollar and has an effective life
of seven to 12 years, is implanted just beneath the skin below the collarbone.
The wires are then threaded into position through veins leading back to the
heart. Most pacemakers have a device that senses when the heartbeat reaches a
certain level; they then turns themselves off until the heartbeat slows again,
usually to 60 beats per minute, and then resume working. These are called
A more sophisticated type
of pacemaker actually monitors a number of physical changes in the body that
signal an increase or decrease in activity. If the heart's own pacing system
fails to respond properly, these pacemakers slowly raise or lower the heartbeat
to the appropriate level, usually from 60 to 100 beats per minute.
We may still see warnings
posted in public places when there is a microwave oven nearby, such as
convenience stores. Today, however, pacemakers are shielded from these
electromagnetic forces and have a backup mechanism if a very strong
electromagnetic field does manage to disrupt the programming.
American Heart Association, National Heart,
Lung, and Blood Institute