Atrial fibrillation: Preventing strokes

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Atrial fibrillation increases the risk of a stroke. Anticoagulants (medicine that prevents blood clots) can greatly reduce this risk. It is particularly worth considering if you have other risk factors for a stroke.

Atrial fibrillation is the most common kind of irregular heartbeat. It usually doesn’t pose an immediate threat to your health, but increases your risk of a stroke in the long term. Taking tablets that prevent blood clots (oral anticoagulants) can greatly reduce this risk and increase life expectancy. This has been proven in many large studies.

For many (but not all) people who have , it's a good idea to take medication to prevent strokes. Your doctor can help you to estimate your personal risk of having a stroke.

How high is your risk of a stroke, and how can you reduce it?

Some people with will be more likely than others to have a stroke, depending on which other risk factors they have. You can estimate your personal risk of having a stroke by calculating what is known as your CHA2DS2-VASc score. This score describes the likelihood that you will have a stroke within the next year. It is calculated by adding up points for the following different risk factors:

Table: Risk factors for a stroke and their score
Risk factor Points
Aged between 65 and 74 years 1
Older than 75 years 2
Already had a stroke in the past 2
Diabetes 1
High blood pressure 1
Heart failure 1
Being a woman 1
Narrow blood vessels due to arteriosclerosis – e.g. coronary artery disease or peripheral arterial occlusive disease (PAOD) 1

Depending on how many risk factors someone has, they will get a score of between 0 and 9. Here “0” means “no other risk factors” and “9” means “all risk factors.” For instance, if a man has high blood pressure and is older than 75, he will have a CHA2DS2-VASc score of 3. The biggest risk factors are older age and already having had a stroke in the past.

The point for the risk factor “female” only counts if the woman has at least one other risk factor.

The following table shows how high the risk of a stroke is for people with different scores – without and with medication.

For example: A total score of 3 points means that, without treatment,

  • 37 out of 1,000 people will have a stroke within one year.

If 1,000 people at this risk level take anticoagulants, only

  • 13 of them will have a stroke.
Table: Risk of a stroke, with and without treatment, over a period of one year
Risk of a stroke
(CHA2DS2-VASc score)
Number of people who do not take anticoagulants and have one stroke per year Number of people who do take anticoagulants and have one stroke per year
0 2 out of 1,000 1 out of 1,000
1 6 out of 1,000 2 out of 1,000
2 25 out of 1,000 9 out of 1,000
3 37 out of 1,000 13 out of 1,000
4 55 out of 1,000 19 out of 1,000
5 84 out of 1,000 29 out of 1,000
6 114 out of 1,000 39 out of 1,000

The figures in the table only refer to the risk within a time period of one year. But is a chronic (long-lasting) disease which is treated over a much longer period of time. If the medication is taken for longer, it is more likely to prevent a stroke.

How common are side effects?

The most common side effect of anticoagulants is bleeding. Minor bleeding, like a nosebleed or bleeding gums, usually isn’t a problem. If there is more major bleeding, for instance in the stomach or bowel, a blood transfusion or hospital stay might be needed.

Certain factors increase the risk of bleeding. Having an increased risk of bleeding is rarely seen as a reason not to take anticoagulant medication. But it's a good idea to be aware of any other risk factors for bleeding so that they can be treated.

Your risk of bleeding will depend on whether you have any risk factors other than taking anticoagulant medication. It can be determined using what is known as the HAS-BLED score. The possible risk factors include the following:

  • High blood pressure that isn’t being treated, or isn’t being treated effectively enough
  • Impaired liver function
  • Impaired kidney function
  • Already had a stroke in the past
  • Already had bleeding in the past
  • Poorly controlled blood clotting speed
  • Older than 65 years
  • Taking anti-inflammatory painkillers such as acetylsalicylic acid (the drug in e.g. Aspirin), diclofenac, ibuprofen or naproxen
  • Drinking a lot of alcohol

The more risk factors you have, the greater the risk of bleeding. Some risk factors can be avoided – for instance, by getting proper treatment for high blood pressure, and not drinking much alcohol.

The most serious side effect of anticoagulants is a brain hemorrhage. But the risk of that happening is very low. The likelihood of anticoagulants preventing a stroke is much higher.

It is important to tell your doctors about any anticoagulants you might be taking, especially if you’re planning to have surgery or another procedure. This includes small procedures such as a tooth extraction or a colonoscopy that could lead to bleeding.

Which anticoagulants are used to treat atrial fibrillation?

There are two groups of anticoagulants:

  • Direct oral anticoagulants (DOACs), also known as “novel oral anticoagulants” (NOACs)
  • Vitamin K antagonists (sometimes also called coumarins)

Anticoagulants are taken in the form of a tablet once or twice a day, depending on which drug is used.

Drugs like acetylsalicylic acid (the drug in e.g. Aspirin) which can also prevent blood clots are usually no longer used to treat . This is because they increase the risk of bleeding without preventing strokes effectively enough. They are taken after a though, for instance.

How do vitamin K antagonists work?

For many decades now, vitamin K antagonists (sometimes also called coumarins) have been used in the prevention of strokes. The most commonly used drug of this kind in Germany is called phenprocoumon – known by many under the brand name “Marcumar.” Other brand names of phenprocoumon include Phenprogamma and Falithrom.

Vitamin K agonists achieve their full effect three to seven days after you start taking them. Foods and alcohol that contain vitamin K can alter the effect of these drugs. For that reason, people who take vitamin K antagonists have to regularly check the ability of their blood to clot, and if necessary adjust the dose of their medication:

  • The anti-clotting effect should be strong enough to prevent blood clots from forming.
  • But it shouldn’t be too strong because that increases the risk of bleeding.

The ability of the blood to clot is measured once a week at first. If the readings lie within the target range over a long period of time, they are only measured every few weeks after that.

It is not absolutely necessary to always go to the doctor to have your blood tested. You can attend a patient education class to learn how to measure your blood’s clotting ability at home and how to adjust the dose of medication yourself. Then you only need to go to the doctor every few months.

Studies have shown that people who check their own blood often manage well, and that their blood clotting ability is even better adjusted than if it had been checked in a doctor's practice.

What do you need to watch for in direct oral anticoagulants (DOACs)?

The following four drugs are DOACs:

  • Apixaban (trade name: Eliquis)
  • Dabigatran (trade name: Pradaxa)
  • Edoxaban (trade name: Lixiana)
  • Rivaroxaban (trade name: Xarelto)

DOACs already start working after just a few hours. When you stop taking them, it takes one to four days for the blood's clotting ability to return to normal.

When people use anticoagulants, there is no need to check the clotting ability of their blood. This has pros and cons:

  • Advantage: There is no need to measure blood clotting times and adjust doses. This is particularly helpful if it's difficult to do regular checks – for instance, for practical reasons.
  • Disadvantage: Some people find it hard to take medication every day over the long term. Regular check-ups might give them reassurance. In that case, treatment with vitamin K antagonists might be more suitable for them.

Comparing vitamin K antagonists with direct oral anticoagulants

Various studies have compared the effectiveness of direct oral anticoagulants with that of vitamin K antagonists. Their results suggest that direct oral anticoagulants are somewhat more effective, and a bit less likely to cause bleeding, than vitamin K antagonists are.

When deciding which medication to use, various aspects play a role. They include the following:

  • possible interactions with other medications or foods,
  • kidney function, and
  • the risk of bleeding.

If someone is taking a vitamin K antagonist and is doing well on it, there is no medical reason for them to switch to a DOAC.

No big studies have compared the various direct oral anticoagulants with each other so far. So it's not possible to say for sure which of these medications works the best. Initial findings suggest that apixaban may be a bit more effective than other oral anticoagulants. Dabigatran may somewhat increase the risk of gastrointestinal (stomach and bowel) bleeding.

Is left atrial appendage closure a suitable alternative?

Many of the blood clots that cause strokes develop in a part of the heart known as the left atrial appendage. This is a pouch-like bulge in the left atrium (left upper heart chamber). Various implants can be used to close off the left atrial appendage. The aim is to try to stop blood clots entering the bloodstream from there and causing strokes.

The implants look like tiny parachutes made out of wire mesh. They are placed inside the heart with the help of a cardiac (heart) . The most commonly used implants in Germany are called the "Watchman implant" and the "Amplatzer septal occluder device."

Implants are associated with various disadvantages and risks:

  • Unlike medication, they don’t offer protection from blood clots that develop elsewhere in the heart or bloodstream.
  • Even if you have an implant, you still have to take anticoagulant medication. Blood clots can form on the surface of the implant in the heart, so medication is needed in order to prevent that from happening.
  • Studies found that in 2 to 10% of all people who received an implant, the implant had to be removed again because it wasn't in the right position in the heart. The heart muscle may become damaged during the procedure and then fill with fluid. Severe pericardial effusion (fluid around the heart, also known as cardiac tamponade) is life-threatening because it prevents the heart from pumping properly. Studies found that complications occurred in 4 to 9 out of 100 procedures.

There are also no large studies that have compared the pros and cons of these implants with those of anticoagulant medication alone. So it's not clear whether they prevent strokes equally well.

For all of the above reasons, experts recommend only considering implants in people who aren't able to take anticoagulants due to a high risk of bleeding. This may be the case, for instance, in people who have had a brain hemorrhage in the past, with an unknown cause. But most people can take the medication.

The left atrial appendage can also be surgically closed or removed. But this is only done if someone has to have heart surgery anyway (e.g. surgery).

Making a decision

Whether treatment with medication is a good idea will depend on your individual risk factors for stroke and bleeding. Medical societies recommend treatment with anticoagulants in men who have a CHA2DS2-VASc score of 2 or above, and in women who have a score of 3 or above. Treatment with anticoagulants may even be a good idea in men with a score of 1 or women with a score of 2.

It is helpful to first of all calculate your personal risk of a stroke and bleeding together with your doctor, carefully consider and compare the risks, and then make a joint decision.

When making the decision, it's important to take into account that most bleeding that is caused by medication is easy to treat and doesn't have any long-term consequences. But strokes can be fatal or cause serious – and often permanent – problems such as paralysis and trouble speaking. Many people need nursing care after having a stroke.

The treatment decision doesn't have to be final. If, for instance, further risk factors arise over time, it is a good idea to reconsider the pros and cons of a treatment. Medical societies recommend checking your score regularly – for the first time four to six months after the . Then the treatment can be adjusted if needed.

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IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on January 31, 2023

Next planned update: 2026


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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