Pacemakers
What is a pacemaker?
A pacemaker is an electronic device used to treat patients who
have symptoms caused by abnormally slow heartbeats. A pacemaker is
capable of keeping track of the patient's heartbeats. If the
patient's heart is beating too slowly, the pacemaker will generate
electrical signals similar to the heart's natural signals, causing
the heart to beat faster. The purpose of the pacemaker is to maintain
heartbeats so that adequate oxygen and nutrients are delivered
through the blood to the organs of the body.
What is the normal function of the
heart?
The heart is an organ consisting of four chambers that pump blood.
The two upper chambers are called the right and left atria, and the
two lower chambers are called the right and left ventricles. The
right atrium receives venous blood (oxygen-poor blood) from the body
and pumps it into the right ventricle. The right ventricle pumps the
oxygen-poor blood to the lungs to receive oxygen. The oxygen-rich
blood from the lungs then travels to the left atrium and is pumped by
the left atrium into the left ventricle. The left ventricle delivers
the oxygen-rich blood to the rest of the body. In addition to
oxygen, the blood transports other nutrients (glucose, electrolytes,
etc.) to the organs. In order to keep a body healthy, the heart must
maintain an adequate heartbeat (heart rate) so that sufficient amount
of oxygen and nutrients are delivered by the left ventricle to the
body.
The heartbeat (heart rate) is normally governed by the frequency
of electrical signals which are generated by the heart's natural
pacemaker called the SA node. The SA node is located on the wall of
the right atrium. Electrical signals from the SA node travel along
special conduction tissues on the walls of the atria, causing the
atria muscles to contract and pump. These same electrical signals
then travel to the AV node, a small area in the heart that serves as
an electrical relay station between the atria and the ventricles.
From the AV node, these electrical signals travel along special
conduction tissues to reach the walls of the ventricles, causing the
ventricles to pump.
Normally, the heart can vary the amount of blood delivered to the
body by varying the frequency of the signals originating from the SA
node. When a person is resting and the oxygen consumption of the body
is low, the frequency of signal generation by the SA node decreases,
thus slowing the heart rate. During exercise or excitement, the
frequency of signal generation by the SA node increases and the heart
rate accelerates.
Next: What causes slow heart rates? »
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