Atrial Fibrillation: A Major Suspect in Unexplained Strokes

Medically Reviewed

A cryptogenic stroke is a stroke for which there is no apparent underlying cause. Such strokes are more common than we’d like to think: About one of every four ischemic strokes is classified as cryptogenic.

The number is even greater for transient ischemic attacks (TIAs). Sometimes referred to as mini-strokes, TIAs produce short-lived stroke symptoms and usually cause no permanent injury to the brain. However, TIAs are often precursors of a major stroke that might have been prevented if the cause was known. But nearly half of all TIAs are cryptogenic.

Having a stroke or a TIA significantly raises your risk for having another. So knowing what caused the stroke or TIA and what you can do to prevent further occurrences could save your life. Atrial fibrillation, also called AF or AFib, is a major suspect in strokes of no known cause.

Although atrial fibrillation is the most common form of abnormal heart rhythm, it can be hard to detect because, in many cases, it doesn’t cause symptoms.

With that in mind, the latest guidelines from the American Heart Association/American Stroke Association for preventing recurring strokes focus greater attention on identifying atrial fibrillation and preventing the strokes it causes.

A symptomless threat

Atrial fibrillation, even when it occurs without symptoms, is a major cause of stroke. With atrial fibrillation, electrical signals that control the contractions of heart muscle are erratic. It’s these contractions that move blood from one chamber of the heart to the next and then from the heart to the rest of the body.

But with atrial fibrillation, contractions may become too rapid or too random or chaotic to allow the heart’s chambers to fill and empty properly. When that occurs, blood flow becomes inconsistent.

The result is that blood starts to pool in the upper chambers, known as the atria. When it pools, it also starts to clot, and it’s this clotting that causes the stroke risk.

Pieces can break off from a clot, be passed from one chamber to the next, and then out into the body, where they travel through the arteries. Eventually, some arrive at the brain, where they continue to travel through smaller and smaller vessels. If a clot becomes entrapped, it shuts off the flow of blood to the part of the brain that vessel supplies. This causes a stroke.

Atrial fibrillation causes one of every six strokes, and such strokes are usually major. As many as 8 of every 10 patients with a stroke brought on by atrial fibrillation die or are disabled. But if atrial fibrillation is recognized and treated early enough, most of those strokes can be prevented.

The key is anticoagulation therapy. Regular treatment with powerful drugs such as warfarin (Coumadin) or one of the newer anticoagulants, such as dabigatran (Pradaxa), rivaroxaban (Xarelto), apixaban (Eliquis), or edoxaban (Savaysa), can help break up clots and prevent new ones from forming.

These drugs are not without risk, particularly the risk of bleeding, and their use needs to be carefully monitored. Dietary restrictions may need to be followed and precautions taken before you undergo any medical procedures. And anticoagulant therapy is not short-term; for many patients, it can last a lifetime.

But for most people, the protection against stroke this therapy provides outweighs the risks and restrictions that come with it.

Longer monitoring

To pinpoint the cause of a stroke brought on by a blood clot, doctors need to know where the clot originated. One of the tests they use is an electrocardiogram, or ECG, which measures the electrical activity of the heart.

Because atrial fibrillation stems from a problem with electrical signals controlling heart rhythm, an ECG can show atrial fibrillation even when there are no symptoms.

Previous guidelines recommended monitoring the heart for signs of atrial fibrillation for a period of 24 hours. The problem is that episodes of atrial fibrillation can be unpredictable. They may come and go at random. Or they can be chronic and range from several days in length to being present all the time. As a result, researchers pointed out that 24 hours may not be enough time to identify all relevant cases of atrial fibrillation.

Two recent studies published in the same issue of The New England Journal of Medicine illustrate the advantage of monitoring longer than 24 hours. One study followed more than 500 patients over the age of 55. It found five times more cases of atrial fibrillation in patients monitored over 30 days (16 percent) than were found in patients after 24 hours of monitoring (3 percent). The second study used an insertable monitoring device, followed patients over 12 months, and had very similar results.

Because of even larger studies similar to those, the guidelines were updated in 2014 to recommend monitoring for atrial fibrillation for 30 days after a stroke with no identifiable cause.

Preventing the first stroke

You needn’t have had a first stroke to benefit from anticoagulation therapy. If you have atrial fibrillation, taking anticoagulation medicines can help keep that first stroke from happening, reducing the risk by at least 50 percent.

Atrial fibrillation can happen at any age and without any apparent cause, but two major risk factors are age and underlying heart disease. The older you are, the greater your risk. Also, you can have atrial fibrillation with no symptoms. It’s important to talk with your doctor about your risk and about a schedule for ECG monitoring.

Since atrial fibrillation can be sporadic and hard to pinpoint, let your doctor know as soon as possible about any symptoms you might have. Doing so could save your life. Here are symptoms to watch for:

Quivering or fluttering heartbeat

Feeling like your heart is racing or beating irregularly

Fluttering or thumping in the chest


Shortness of breath


Fainting (a result of less blood getting to the brain)

Confusion (another result of less blood to the brain)

Sometimes the symptoms can mimic those of a heart attack. But don’t gamble—call 911 right away if you experience any of the following:

Pain or discomfort in the center of your chest that lasts for more than a few moments

Chest pain or an uncomfortable feeling in your chest that goes away and comes back

Pain or discomfort in your arm, neck, jaw, back or stomach

Difficulty breathing

Other symptoms such as breaking out in a cold sweat or feeling nauseated or lightheaded.