Pacemaker (cont.)
Understanding the Heart's Electrical System
Your heart has its own internal electrical system that controls the rate and
rhythm of your heartbeat. With each heartbeat, an electrical signal spreads from
the top of your heart to the bottom. As the signal travels, it causes the heart
to contract and pump blood.
Each electrical signal normally begins in a group of cells called the sinus
node or sinoatrial (SA) node. As the signal spreads from the top of the heart to
the bottom, it coordinates the timing of heart cell activity.
First, the heart's two upper chambers, the atria (AY-tree-uh), contract. This
contraction pumps blood into the heart's two lower chambers, the ventricles
(VEN-trih-kuls). The ventricles then contract and pump blood to the rest of the
body. The combined contraction of the atria and ventricles is a heartbeat.
Who Needs a Pacemaker?
Doctors recommend pacemakers for a number of reasons. The most common reasons
are bradycardia and heart block.
Bradycardia is a slower than normal heartbeat. Heart block is a problem with
the heart's electrical system. The disorder occurs when an electrical signal is
slowed or disrupted as it moves through the heart.
Heart block can happen as a result of aging, damage to the heart from a heart
attack, or other conditions that interfere with the heart's electrical activity.
Certain nerve and muscle disorders also can cause heart block, including
muscular dystrophy.
Your doctor also may recommend a pacemaker if:
- Aging or heart disease damages your sinus node's ability to set the correct
pace for your heartbeat. Such damage can cause slower than normal heartbeats or
long pauses between heartbeats (as discussed above). The damage also can cause
your heart to alternate between slow and fast rhythms. This condition is called
sick sinus syndrome.
- You've had a medical procedure to treat an arrhythmia called atrial
fibrillation. A pacemaker can help regulate your heartbeat after the procedure.
- You need to take certain heart medicines, such as
beta blockers. These
medicines may slow your heartbeat too much.
- You faint or have other symptoms of a slow heartbeat. For example, this may
happen if the main artery in your neck that supplies your brain with blood is
sensitive to pressure. Just quickly turning your neck can cause your heart to
beat slower than normal. If that happens, not enough blood may flow to your
brain, causing you to feel faint or collapse.
- You have heart muscle problems that cause electrical signals to travel too
slowly through your heart muscle. (Your pacemaker may provide cardiac
resynchronization therapy for this problem.)
- You have long QT syndrome, which puts you at risk for dangerous
arrhythmias.
Children, adolescents, and people who have certain types of
congenital heart
disease may get pacemakers. Pacemakers also are sometimes implanted after heart
transplants.
Before recommending a pacemaker, your doctor will consider any arrhythmia
symptoms you have, such as dizziness, unexplained fainting, or shortness of
breath. He or she also will consider whether you have a history of heart
disease, what medicines you're currently taking, and the results of heart tests.
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