Pacemaker (cont.)
How Does a Pacemaker Work?
A pacemaker system consists of a battery, a computerized generator, and wires
with sensors called electrodes on one end. The battery powers the generator, and
both are surrounded by a thin metal box. The wires connect the generator to the
heart.
A pacemaker monitors and helps control your heartbeat. The electrodes detect
your heart's electrical activity and send data through the wires to the computer
in the generator.
If your heart rhythm is abnormal, the computer will direct the generator to
send electrical pulses to your heart. The pulses then travel through the wires
to reach your heart.
Newer pacemakers also can monitor your blood temperature, breathing, and
other factors and adjust your heart rate to changes in your activity.
The pacemaker's computer also records your heart's electrical activity and
heart rhythm. Your doctor will use these recordings to adjust your pacemaker so
it works better for you.
Your doctor can program the pacemaker's computer with an external device. He
or she doesn't have to use needles or have direct contact with the pacemaker.
Pacemakers have one to three wires that are each placed in different chambers
of the heart.
- The wires in a single-chamber pacemaker usually carry pulses between the
right ventricle (the lower right chamber of your heart) and the generator.
- The wires in a dual-chamber pacemaker carry pulses between the right atrium
(the upper right chamber of your heart) and the right ventricle and the
generator. The pulses help coordinate the timing of these two chambers'
contractions.
- The wires in a biventricular pacemaker carry pulses between an atrium and
both ventricles and the generator. The pulses help coordinate electrical
signaling between the two ventricles. This type of pacemaker also is called a
cardiac resynchronization therapy (CRT) device.
Cross-Section of a Chest With a Pacemaker
The illustration shows a cross-section of a chest with a pacemaker. Figure A
shows a double-lead, or dual-chamber, pacemaker in the upper chest. The wires
with electrodes are inserted into the heart's right atrium and ventricle through
a vein in the upper chest. Figure B shows the electrode stimulating the heart
muscle. Figure C shows a single-lead, or single-chamber, pacemaker in the upper
chest. The wire with the electrode is inserted into the heart's right ventricle
through a vein in the upper chest.
Types of Pacemaker Programming
The two main types of programming for pacemakers are demand pacing and
rate-responsive pacing.
A demand pacemaker monitors your heart rhythm. It only sends electrical
pulses to your heart if your heart is beating too slow or if it misses a beat.
A rate-responsive pacemaker will speed up or slow down your heart rate
depending on how active you are. To do this, the rate-responsive pacemaker
monitors your sinus node rate, breathing, blood temperature, and other factors
to determine your activity level.
Most people who need pacemakers to continually set the pace of their
heartbeats have rate-responsive pacemakers.
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