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Atrial Fibrillation and Stroke

What is Atrial Fibrillation?

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Updated June 25, 2008

Atrial Fibrillation and Stroke
ADAM
Atrial fibrillation is a type of arrhythmia in which the upper chambers of the heart (the atria) beat erratically. This erratic beating can be extremely fast (in excess of 300 beats per minute), making it difficult for blood to circulate freely from the atria into the lower chambers of the heart, known as the ventricles. Atrial fibrillation can be a transient event, a recurrent event, or a permanent condition.

What Causes Atrial Fibrillation?

Most cases of atrial fibrillation can be attributed to diseases that affect the structure of the heart over many years, which is one of the main reasons why atrial fibrillation is most common in older adults. For instance, years of untreated high blood pressure force the heart muscle to work overtime in order to maintain normal blood flow through the body. This extra work makes the heart muscle increase in size, a condition known as cardiomegaly. As the size of the heart increases, its muscle becomes stiff, and the chances of developing atrial fibrillation increase. Other disorders that can lead to atrial fibrillation include diseases of the heart valves (such as rheumatic heart disease), swelling (pericarditis) or fluid around the heart (pericardial effusions), prior heart attacks, and diseases of the electrical conduction system of the heart (such as sick sinus syndrome).

Not all conditions that cause atrial fibrillation do so by affecting the heart directly. For instance, the overproduction of thyroid hormones by the thyroid gland, (hyperthyroidism) can lead to atrial fibrillation, as can several lung diseases and infections, such as pneumonia.

Atrial fibrillation can also be induced by emotional or physical stress, alcohol, nicotine, and caffeine.

What Are The Symptoms of Atrial Fibrillation?

People with atrial fibrillation often report palpitation -- a feeling that the heart is beating extremely fast. For some, this rapid and disorganized heart beat may be so extreme that blood flow through the heart chambers is profoundly impaired. This may cause fainting, chest pain, or even a temporary choking sensation.

How is Atrial Fibrillation Diagnosed?

Atrial fibrillation is easily diagnosed with an electrocardiogram, also known as an EKG. If a patient has atrial fibrillation, the test will show a rapid and irregular heart beat in which contractions of the upper chambers of the heart range between 300 and 500 per minute; contractions by the lower chambers (the pulse rate) will range from 120 to 170 beats per minute. If atrial fibrillation comes and goes, a doctor will prescribe a portable heart monitor known as a Holter monitor to make the diagnosis. The patient will carry the monitor, which can record even very brief episodes of atrial fibrillation, around for 24 to 48 hours.

How is Atrial Fibrillation Treated?

The treatment of atrial fibrillation aims to control the heart rate, as the abnormal rhythm can spread from the atria to the ventricles and cause the entire heart to beat so fast that the heart muscle itself becomes severely compromised. In people with severe heart disease, atrial fibrillation can even lead to a heart attack. Common medications prescribed by doctors to control heart rate include beta-blockers, such as metoprolol, and other agents, such as digoxin and diltiazem. In select cases, doctors can shock the heart and stop the abnormality that is causing the atrial fibrillation.

An important aspect of atrial fibrillation treatment is thinning of the blood with a medication called coumadin. (see below)

Why Does Atrial Fibrillation Cause Strokes?

Depending on the age of a person, and the specific cause of chronic atrial fibrillation, the incidence of stroke in people with this disorder can range from 5 to 17-fold higher than that of people without atrial fibrillation. Most commonly, atrial fibrillation causes cardioembolic strokes -- those caused by a clot that escapes from the heart and blocks a blood vessel in the brain. Blood clots are known to form whenever blood remains static for prolonged periods of time, or as a result of turbulent blood flow, both of which are likely to occur during the erratic and disorganized heart beat of atrial fibrillation.

Sources:
Barker Fiebach, and Zieve, Principles of Ambulatory Medicine, Seventh Edition, Baltimore, Williams and Wilkins.
Bradley G Walter, Daroff B Robert, Fenichel M Gerald, Jancovic, Joseph Neurology in clinical practice, principles of diagnosis and management. Fourth Edition, Philadelphia, Elsevier, 2004.

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