What Is an Arrhythmia?
An arrhythmia (ah-RITH-me-ah) is a problem with the
speed 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. A heartbeat that is too slow is called bradycardia.
Most arrhythmias are harmless, but some can be
serious or even life threatening. When the heart rate is too slow, too fast, 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 Hearts Electrical
System
The heart has an internal electrical system that
controls the speed and rhythm of the heartbeat. With each heartbeat, an
electrical signal spreads from the top of the heart to the bottom. As it
travels, the electrical signal 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 to the right and left atria. This causes the atria to
contract and pump blood into the hearts 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 hearts electrical
system and a detailed animation, go to the Diseases and Conditions Index
article on
How
the Heart Works.
Overview
There are many different types of arrhythmia. Most
arrhythmias are harmless but some are not. The outlook for a person with an
arrhythmia depends on the type and severity of the arrhythmia. Even serious
arrhythmias can often be successfully treated. Most people with arrhythmias are
able to live normal, healthy lives.
May 2007 |