Atrial Fibrillation Explained

human heart
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Heart disease is one of the leading causes of a stroke. Atrial fibrillation is a type of heart 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 as it should. Atrial fibrillation can be a transient event, a recurrent event, or a permanent condition.


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 or exacerbated by emotional or physical stress, alcohol, nicotine, and caffeine.


People with atrial fibrillation often report palpitations—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.


Atrial fibrillation is easily diagnosed with a test called an electrocardiogram, also known as an EKG. If you have atrial fibrillation, your EKG may 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 your atrial fibrillation comes and goes, your doctor may request a portable heart monitor known as a Holter monitor to make the diagnosis. You would carry the monitor with you for a few days, and it can record even very brief episodes of atrial fibrillation. A new implantable heart monitor can make detection of atrial fibrillation easier.


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.

Medications to control heart rate and rhythm may be prescribed for atrial fibrillation. 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 may include blood-thinning medications such as aspirin, which can help prevent a blood clot from forming. Blood clots formed in the heart due to atrial fibrillation can lead to stroke.

The Risk of Stroke

The incidence of stroke in people with atrial fibrillation can range from five 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.


A Word From Verywell

Atrial fibrillation is a relatively common heart problem.  Your routine medical check-ups already test for atrial fibrillation. Most people who are diagnosed with atrial fibrillation are very well controlled with medication. If you have atrial fibrillation, you need to make sure to maintain regular follow-up appointments with your health care team.


Individualising Anticoagulant Therapy in Atrial Fibrillation Patients, Alings M, Arrhythm Electrophysiol Rev. 2016 Aug;5(2):102-9.

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