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The Heart's Electrical System
The heart's rhythmic contractions depend on
its electrical system, which conducts electrical impulses throughout
the heart.
The sinus node, a group of specialized
cells in the right atrium, is the place where the electrical impulse
normally begins. The sinus node functions as the heart's "natural
pacemaker," setting the pace for the heartbeat.
The electrical impulse travels a set path and
spreads throughout the atria, causing them to contract and squeeze
blood into the ventricles.
From the atria, the electrical impulse reaches
the atrioventricular node, or AV node, which is located between
the atria and the ventricles.
The AV node is like a "relay station,"
slowing down each electrical impulse before it is allowed to pass
through to the ventricles.
The impulse then travels to the ventricles through
a system of specialized muscle fibers. The system divides into a
network of smaller fibers, which distribute the impulse throughout
both ventricles. The impulse stimulates the ventricles, causing
them to contract and pump blood.
Abnormal Heart Rhythms
An abnormal heart rhythm, or arrhythmia, is a change
in either the speed or pattern of the heartbeat. During an arrhythmia,
the heart may beat too slowly, too rapidly, or irregularly.
An arrhythmia may be experienced as a skipping
or fluttering sensation in the chest (palpitation). It may also
cause light-headedness, a fainting spell, chest pain, or shortness
of breath. Sometimes, arrhythmias may go unnoticed.
An arrhythmia becomes serious when the heart beats
too slowly or too rapidly to pump blood effectively, or when there
is a threat to the person's life.
How Doctors Diagnose Arrhythmias
Your doctor may order one or more diagnostic tests to confirm
an arrhythmia and determine whether it is causing your symptoms.
The electrocardiogram (ECG) is a simple
test that records the electrical activity of your heart. The ECG
tracing is a series of waves that represent the electrical events
in the heart. By carefully examining the sequence of events on the
ECG, doctors are able to diagnose arrhythmias.
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