How can atrial fibrillation (AFib) cause a stroke?

Dr. Reza E. Jahan, MD

Atrial fibrillation, a type of irregular heartbeat, could cause a blood clot to form in your heart. This clot could be pumped into a blood vessel in your brain and lead to a stroke. If you have atrial fibrillation, work with your doctor to manage it. Taking blood thinners can help prevent a clot from forming.

Picture a swamp with thick, mucky water. If you have atrial fibrillation, the upper chambers of your heart may contain pools of similarly stagnant blood, since your heart muscle isn’t pumping it all out efficiently. Over time, clots can form in stagnating blood. If one of these clots sneaks out of the heart, it can and often does migrate to your brain, and form a roadblock in a blood vessel, preventing blood with oxygen and nutrients from passing by. The result is a stroke. Starved of the oxygen and nutrients your blood normally delivers, parts of your brain tissue die. So the faster you get yourself to a certified stroke center, the more likely you will have brain left.

Atrial fibrillation occurs when the top part of the heart (the atrium) does not pump blood efficiently into the lower part of the heart (the ventricle). When this occurs, blood can sit in the atrium and form a clot. This clot can then travel to the lower part of the heart and be pumped into the brain, where it can block blood flow and cause a stroke.

Dr. Jeffrey M. Saver, MD

Atrial fibrillation is an abnormal electrical rhythm of the heart that causes the heart muscle of the upper chamber (the atrium) to wriggle irregularly rather than to pump in a coordinated fashion. As a result, blood tends to stop and pool in the upper chamber, and whenever blood stops flowing, it tends to clot. If a clot forms, it can then break off from the heart wall and travel to block a brain artery, causing a stroke.

Your chances of having a stroke increase three to five times if you have atrial fibrillation (Afib). Here's what can happen:

  • Blood left behind. Because the atria are not pumping normally, not all the blood gets pumped out of them. This can cause blood to pool in the atria.
  • Clotting. The blood that pools in the atria can form blood clots.
  • A clot in an artery. A blood clot in the heart can move into the arteries that feed`your body. If a clot enters an artery that leads to your brain and blocks the blood flow, it causes a stroke.

During atrial fibrillation, the upper chambers of the heart quiver rapidly rather than contract forcefully. Blood pools along the walls of the left atrium, eventually forming clots that may break free to travel through the left ventricle to the aorta. If the clot lodges in an artery to the brain, it may obstruct blood flow downstream and cause an ischemic stroke.

Dr. Steven A. Meyers, MD
Diagnostic Radiologist

Atrial fibrillation is a condition where the heart beats irregularly allowing for clots to form in the upper chamber, the atria. These clots can break loose and travel to the brain causing a stroke. The risk of stroke in atrial fibrillation can be greatly reduced by taking anticoagulants such as warfarin or a new medication, dabigatran.

Having a stroke is the biggest risk when you have atrial fibrillation. Your heart doesn't pump out all the blood in its chambers with each beat, so a small amount of blood may pool and form clots. If a blood clot gets pumped into a brain artery, it can block it and cause a stroke. To help prevent a stroke, your doctor may prescribe a medication that "thins" the blood, preventing blood clots in the first place.

Dr. Douglas E. Severance, MD
Family Practitioner

Certain arrhythmias, including atrial fibrillation, increase the risk of stroke. With atrial fibrillation, the atria in the heart quivers, making it unable to pump blood throughout the body effectively. This can cause the blood to pool, which can lead to the formation of blood clots. Once a blood clot breaks away, it can go straight to the brain and block an artery, leading to a brain attack or stroke. With a stroke, there can be mild, moderate, or severe damage to the brain. Sometimes strokes lead to death. The good news with atrial fibrillation is that strokes can be prevented by staying on the medication regimen your doctor prescribes. Specifically, the blood thinning medications such as warfarin (Coumadin), aspirin, and heparin can help prevent blood clots and strokes.

People with atrial fibrillation have a sevenfold increase in the risk of stroke because this condition makes the blood more prone to clotting. If a clot forms in the heart and travels to the brain, this can cause a stroke.

Dr. Jose A. Nazari, MD
Cardiac Electrophysiologist
During atrial fibrillation the blood is stagnant in the atria (the upper chamber of the heart), where it can clot. The clot can travel to other parts of the body including the brain. Atrial fibrillation is the most common cause of stroke.
Dr. Mohammad E. Mortada, MD
Cardiologist (Heart Specialist)

Atrial fibrillation (AF) can cause stroke because blood cannot flow through the upper chambers of the heart (atria) smoothly. With sluggish blood flow, blood clots may form in the atria, especially the left atrium. These blood clots can break away from the heart and travel through the blood vessels. If a blood clot lodges in a blood vessel in the brain, the result is a stroke. About 11% of strokes in the United States are thought to be a direct result of atrial fibrillation. The risk for stroke is three to five times greater with AF and increases with age.

Dr. Ronald M. Firth, MD
Family Practitioner

Your chances of having a stroke increase 3 to 5 times if you have Afib. Here’s what can happen:

  • Blood left behind: because the atria are not pumping normally, not all the blood gets pumped out of them. This can cause blood to pool in the atria.
  • Clotting: the blood that pools in the atria can form blood clots.
  • A clot in an artery: a blood clot in the heart can move into the arteries that feed your body. If a clot enters an artery that leads to your brain and blocks the blood flow, it causes a stroke.
Dr. James C. Ong, MD
Cardiologist (Heart Specialist)

Learn the risk factors associated with stroke in patients with atrial fibrillation. Watch this video with cardiologist James Ong, MD, from West Hills Hospital & Medical Center.

People who have atrial fibrillation, a condition in which the heart does not pump properly, are at an increased of suffering an ischemic stroke. Because their heart pumps irregularly, pools of blood are created—posing a risk for clots. This condition can be treated with medication.

Dr. Charles A. Joyner, MD
Cardiac Electrophysiologist

Because of the ineffective contractions of the atrial chambers themselves, the blood is not ejected as it should be, so it tends to pool and stagnate. It’s like the edges of a stream or river where the water flow isn’t fast, you can see that it swirls around and becomes more still. When this happens, the blood can thicken and form a clot, which resides in the atrium. In unfortunate circumstances, that clot can break free and enter other organs, such as the brain, causing a stroke.

Dr. Theodore K. Chow, MD
Cardiologist (Heart Specialist)

When patients develop AFib, they are at a significant risk for stroke. Watch Theodore Chow, MD, of Regional Medical Center, explain why.

Your heart’s beating is governed by a series of natural electrical impulses that cause the chambers of the heart to contract in a carefully timed sequence.

Atrial fibrillation (AF) is a condition in which the electrical system in the heart does not function properly. The two small upper chambers of the heart (the atria) quiver instead of beating normally. In AF, this lack of normal atrial contractility can cause blood to pool in the heart, increasing the risk of a clot forming. Clots in the heart often break loose and can travel anywhere in the body. If the clot goes to the brain, it will cause a stroke.

This risk of a stroke can be significantly reduced by taking blood thinners, such as Coumadin or Pradaxa. Anyone with a history of atrial fibrillation should discuss taking blood thinners with their doctor. According to the National Institute of Neurological Disorders and Stroke, a person with AF has a stroke risk that is 4 to 6 times greater than those without AF. Stroke risk in people with AF increases with age.

Joan Haizlip, MSN
Cardiologist (Heart Specialist)

People with atrial fibrillation are more likely to have strokes than those who have normal heart rhythms. When you have atrial fibrillation, the upper chambers of the heart (atria) beat up to four times faster than the rest of the heart. They are not able to pump blood out of the atria effectively. As a result, blood can pool and form blood clots.

If these blood clots get pumped out of the heart, they can go to your brain and cause a stroke or a 'brain attack". A stroke can leave you with trouble walking, talking or even speaking.    

That's why your healthcare provider will treat your atrial fibrillation with a special medicine, called a blood thinner. Treating the atrial fibrillation with a blood thinner such as warfarin (Coumadin), heparin, or aspirin may prevent blood clots and strokes from happening.

Dr. Saumil R. Shah, MD
Cardiac Electrophysiologist

Atrial fibrillation increases the risk of stroke. Over 90 percent of strokes with atrial fibrillation originate within the left atrial appendage. This is a small pouch off the left atrium (top chamber) of the heart. Blood can pool in this pouch, increasing the risk of a blood clot. This blood clot can dislodge from the appendage, travel via the aorta to one of the arteries in the brain, and cut off oxygen supply to a portion of the brain, causing stroke.

Dr. Navid Kazemi, MD
Cardiologist (Heart Specialist)

Atrial fibrillation (AFib) is one of the most common causes of stroke. Watch as Navid Kazemi, MD, a cardiologist at MountainView Hospital, explains why it's critical for heart patients to be evaluated for AFib.

Continue Learning about Stroke Risk Factors

Stroke Risk Factors

Stroke Risk Factors

Your risk level for stroke can vary based on your genes and lifestyle; risk factors can also differ between men and women. While you can't control your age, family history, race and gender, it's important to know your stroke risk. ...

Men are at a higher risk for stroke, but women account for more deaths from it. Common risk factors for men and women that can be controlled or treated include high blood pressure, diabetes, cigarette smoking, diet, physical activity and heart disease. Less common risk factors affecting women include migraines, taking the pill, pregnancy and childbirth complications and use of hormone replacement therapy. Learn more about stroke risk factors with expert advice from Sharecare.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.