Atrial Fibrillation Overview


You may be surprised to learn that atrial fibrillation, an abnormal heart rhythm, follows heart failure as the most common type of heart disease. More than 2.2 million people in the United States suffer from heart disease caused by irregular heart rhythm, and worldwide more than 5 million are affected.

Because risk increases with age, it is expected that the number of people over the age of 80 with atrial fibrillation will quadruple in the next seven to eight years. In this article you will learn what atrial fibrillation is, how it works, its potential dangers, and what causes it.

Arrhythmia: A Faulty Heart Rhythm

The four chambers of the heart
The four chambers of the heart

The heart is a pumping machine that moves blood to the lungs, and then once the blood is filled with oxygen, to the body's organs. But the heart is also a rhythm machine with finely tuned electrical circuits. It is actually this electrical system that starts and keeps the pumping mechanism moving.

The heart's electrical circuit begins in the right atrium, one of the heart's two upper chambers, with a signal originating in a group of specialized cells called the sinoatrial node or SA node. The SA node is often called the heart's natural pacemaker because it literally sets the pace at which the heart beats.

The heart's electrical system The heart's electrical system
The heart's electrical system

The electrical signal spreads from the right atrium to the left atrium and then travels down to the ventricles, the heart's two lower chambers. In response to the electrical signal, the ventricles' muscle cells contract and pump blood into the arteries. (See "How the Heart Works" for more information).

When the heart is healthy, it has a normal rhythm between 60 and 100 beats per minute (bpm). When the heart's rhythm is slower or faster than normal, the rhythm is considered to be abnormal and is called an arrhythmia. Arrhythmias can occur in either the ventricles or the atria, and sometimes occur in both the upper and lower heart chambers.

Atrial fibrillation -- also called AF or A-Fib -- is the most common arrhythmia. In the next section, we'll see what what it is.

Stroke, Heart Disease and Atrial Fibrillation

Atrial fibrillation is a term that defines both the location and the nature of one particular type of arrhythmia. The abnormal rhythm originates in the atria and it has a fibrillating nature. Fibrillation is characterized by rapid, chaotic quivering. In atrial fibrillation, the rhythm is circular and unorganized, and the rhythm in the atria increases to 300 to 600 beats per minute -- as much as six times faster than a normal heartbeat.

If left untreated, the rapid, chaotic beating of atrial fibrillation can weaken the heart muscle. Over time, the heart stretches, grows thicker, and has increasing difficulty in contracting and pumping blood properly.

This condition, known as heart failure, is serious and potentially life-threatening. People with atrial fibrillation are also at increased risk of stroke. Because the heart's chambers are not efficiently emptied, blood can pool and sometimes clot. If a clot in the atria breaks loose and travels to the arteries in the brain, a stroke can result. About 15 percent of the 700,000 strokes that occur in the United States each year -- approximately 105,000 -- occur in people with atrial fibrillation.

Atrial fibrillation is associated with high blood pressure, hardening of the arteries, heart failure, coronary artery disease, and other types of heart disease, such as valve disease, pericarditis (inflammation of the heart membrane), congenital heart defects, and with chronic lung diseases. It may also be caused by factors unrelated to the heart, such as diabetes and thyroid disease, certain medications, diet, stress, and environmental toxins. While many of the atrial fibrillation risk factors can be controlled by lifestyle changes, aging impacts everyone despite our best efforts to slow its effects. If you are 50 years old or younger, your risk for atrial fibrillation is one in every 100 people, but by the time you are over 80 years, your risk increases tenfold to one in every 10 people.

For more information on atrial fibrillation and other heart topics, check out the links on the next page.

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