What Is an Arrhythmia?
An arrhythmia (ah-RITH-me-ah) is a problem with the
rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too
fast, too slow, or with an irregular rhythm.
A heartbeat that is too fast is called tachycardia
(TAK-ih-KAR-de-ah). A heartbeat that is too slow is called bradycardia
(bray-de-KAR-de-ah).
Most arrhythmias are harmless, but some can be
serious or even life threatening. When the heart rate is too fast, too slow, or
irregular, the heart may not be able to pump enough blood to the body. Lack of
blood flow can damage the brain, heart, and other organs.
Understanding the Heart's Electrical System
To understand arrhythmias, it helps to understand
the heart's internal electrical system. The heart's electrical system controls
the rate and rhythm of the heartbeat.
With each heartbeat, an electrical signal spreads
from the top of the heart to the bottom. As the signal travels, it causes the
heart to contract and pump blood. The process repeats with each new
heartbeat.
Each electrical signal begins in a group of cells
called the sinus node or sinoatrial (SA) node. The SA node is located in the
right atrium (AY-tree-um), which is the upper right chamber of the heart. In a
healthy adult heart at rest, the SA node fires off an electrical signal to
begin a new heartbeat 60 to 100 times a minute.
From the SA node, the electrical signal travels
through special pathways in the right and left atria. This causes the atria to
contract and pump blood into the heart's two lower chambers, the ventricles
(VEN-trih-kuls).
The electrical signal then moves down to a group of
cells called the atrioventricular (AV) node, located between the atria and the
ventricles. Here, the signal slows down just a little, allowing the ventricles
time to finish filling with blood.
The electrical signal then leaves the AV node and
travels along a pathway called the bundle of His. This pathway divides into a
right bundle branch and a left bundle branch. The signal goes down these
branches to the ventricles, causing them to contract and pump blood out to the
lungs and the rest of the body.
The ventricles then relax, and the heartbeat process
starts all over again in the SA node.
A problem with any part of this process can cause an
arrhythmia. For example, in
atrial
fibrillation, a common type of arrhythmia, electrical signals travel
through the atria in a fast and disorganized way. This causes the atria to
quiver instead of contract.
For more information on the heart's electrical
system and detailed animations, go to the Diseases and Conditions Index
How
the Heart Works article.
Outlook
There are many types of arrhythmia. Most arrhythmias
are harmless, but some are not. The outlook for a person who has an arrhythmia
depends on the type and severity of the arrhythmia.
Even serious arrhythmias often can be successfully
treated. Most people who have arrhythmias are able to live normal, healthy
lives.
Revised July 2009 |