Pacemaker (cont.)
How can an abnormally slow heart rate be
increased?
There is no medicine available in oral (pill) form that can be
taken regularly to increase the heart rate. Currently, the only
method to consistently increase the heart rate is the use of a
pacemaker to send electrical signals to generate heartbeats.
Temporary pacemakers are usually used first, especially if the
abnormally slow heart rate is believed to be transient (lasting only
days) and caused by conditions that are reversible or correctable.
Temporary pacemakers are easily disconnected if the heart rate
returns to normal.
Permanent pacemakers are necessary when the slow heart rate
becomes chronic (lasting more than a few days) or is believed to be
irreversible.
What is the design of permanent pacemakers?
A permanent pacemaker has two parts; the pacemaker chamber and the
lead(s). The pacemaker chamber contains a timing device for setting
the pacing rate, a circuitry that detects electrical signals from the
heart, and a battery.
In some patients who need permanent pacemakers for abnormally slow
heart rates, fluctuations of the heart rate can occur. The pacemaker
is capable of "listening" to the natural electrical signals
from the heart. When the heart is beating normally, the pacemaker
does nothing. When the heart stops beating or beats too slowly, the
pacemaker takes over generating electrical signals for the heart at a
frequency set by the doctor.
While temporary pacemakers are housed in chambers outside of the
body and can use external electrical power sources, permanent
pacemakers are implanted inside the body and therefore need their own
batteries. Most of the modern permanent pacemaker chambers are small,
weighing less than 30 grams. These small, lightweight devices are
comfortable to wear inside the body and are barely visible. The small
batteries inside the pacemaker chambers are also durable. Most
implanted pacemakers have batteries that will last 7-10 years before
needing to be replaced.
The conducting wire(s) that carry electrical signals between the
heart and the pacemaker is usually made of platinum. These wires are
insulated with silicone or polyurethane. The insulted wires are
called leads. Some pacemakers have only one lead, and are called
single-chamber pacemakers. Others have two leads and are called dual-
chamber pacemakers.
The pacemaker lead is inserted through a vein in the chest into
the heart. The tip of the lead is placed in contact with the inner
wall of the right atrium or the right ventricle, while the other end
of the lead is connected to the pacemaker chamber. These leads are
safe, and generally do not injure or cause infections in the veins or
the heart.
Next: How are pacemakers implanted? »
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