Preventing strokes

Photo of pills and a glass of water (PantherMedia / Jörg Schmalenberger)

Atrial fibrillation increases the risk of a stroke. This risk can be greatly reduced by taking medication. But it usually only makes sense to do so if you have other risk factors for cardiovascular disease too.

Atrial fibrillation is the most common kind of irregular heartbeat, and usually doesn’t pose an immediate threat to your health. In the long term, though, it increases your risk of a stroke. This risk can be greatly reduced by taking tablets that inhibit blood clotting (oral anticoagulants). Before deciding on a treatment together with your doctor, it’s a good idea to calculate your personal risk of having a stroke. Treatment with medication isn’t always necessary.

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

Some people with atrial fibrillation 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 is an estimate of 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:  

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
Severe heart failure 1
Female 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 by adding up the points. Here “0” means “no other risk factors” and “9” means “all risk factors.” For instance, if someone has high blood pressure and is older than 75, they will have a CHA2DS2-VASc score of 3. 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 – both for those who are taking medication and for those who aren’t taking medication. Large studies have shown that anticoagulants are very effective at preventing strokes and can increase life expectancy.

For instance, 37 out of 1,000 people with a score of 3 have a stroke within a year. If 1,000 people with this risk take anticoagulants, only 13 of them have a stroke within a year. The column on the right of the table shows how many people don't have a stroke thanks to the medication (24 out of 1,000). 

Table: Risk of a stroke, with and without treatment, over a period of one year
Personal risk of a stroke
(CHA2DS2-VASc score)
Number of strokes without
Number of strokes with
Number of strokes
0 2 out of 1,000 1 out of 1,000 1 out of 1,000
1 6 out of 1,000 2 out of 1,000 4 out of 1,000
2 25 out of 1,000 9 out of 1,000 16 out of 1,000
3 37 out of 1,000 13 out of 1,000 24 out of 1,000
4 55 out of 1,000 19 out of 1,000 36 out of 1,000
5 84 out of 1,000 29 out of 1,000 55 out of 1,000
6 114 out of 1,000 39 out of 1,000 75 out of 1,000

The figures in the table only refer to the risk within a time period of one year. But atrial fibrillation 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 gastrointestinal tract (stomach or bowel), a blood transfusion or hospital stay might be needed.

The risk of bleeding can be determined using what is known as the HAS-BLED score. It will depend on whether the person has risk factors for bleeding other than the fact that they are taking the medication. 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 following table shows how likely major bleeding is. Bleeding is considered to be major if it is so bad that a blood transfusion or hospital stay are needed.

The table can be read as follows: Without anticoagulants, 9 out of 1,000 people who have atrial fibrillation and three risk factors for bleeding will have major bleeding within one year – with anticoagulants, 24 out of 1,000 people will. The right column shows how many of the bleeding events are caused by the medication (15 out of 1,000).

Table: Risk of bleeding without and with anticoagulants over a period of one year
Number of risk factors Number of major bleeding
events without anticoagulants
Number of major bleeding
events with anticoagulants
Number of additional
major bleeding events
1 3 out of 1,000 7 out of 1,000 4 out of 1,000
2 7 out of 1,000 19 out of 1,000 12 out of 1,000
3 9 out of 1,000 24 out of 1,000 15 out of 1,000
4 13 out of 1,000 34 out of 1,000 21 out of 1,000
5 22 out of 1,000 60 out of 1,000 38 out of 1,000

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

If you’re taking anticoagulants, it’s important to tell your doctors that you’re taking them. This is especially important if you’re planning to have surgery or another procedure that could lead to bleeding, such as a tooth extraction or a colonoscopy.

What are the different anticoagulants, and how do they differ?

There are two groups of anticoagulants: vitamin K antagonists and direct oral anticoagulants (DOACs). Direct oral anticoagulants are also known as “novel oral anticoagulants” (NOACs).

In the past, acetylsalicylic acid (the drug in e.g. Aspirin) was sometimes used for the prevention of strokes too. But it isn’t effective enough in atrial fibrillation, so nowadays it is only used in the treatment of other cardiovascular diseases, such as coronary artery disease.

Vitamin K antagonists

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.” It achieves its full effect three to seven days after you start taking it. Other brand names of phenprocoumon include Phenprogamma and Falithrom.

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 isn’t absolutely necessary to always go to the doctor to have your blood tested. You can attend patient education classes 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.

Direct oral anticoagulants (DOACs)

In recent years, four other anticoagulants have been approved in Germany for the prevention of strokes in people who have atrial fibrillation: apixaban, dabigatran, edoxaban and rivaroxaban.

They 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. People who take direct oral anticoagulants don't have to monitor their blood. Some people see this as an advantage, while others see it as a disadvantage: Regularly testing your blood while taking vitamin K antagonists allows you to react if your readings aren't good.

The tests that are used to check your blood's clotting ability don’t work in people who are taking DOACs, so the blood can’t be monitored in that way.

Comparing vitamin K antagonists with direct oral anticoagulants

A few studies have compared the effectiveness of direct oral anticoagulants with that of vitamin K antagonists. Their results suggest that direct oral anticoagulants might be somewhat more effective, and a bit less likely to cause bleeding, than vitamin K antagonists are. But many medical societies consider the two types of medications to be equally good. When deciding which medication to use, other aspects play a more important role. These include possible contraindications (something that makes treatment with a certain medication inadvisable), your personal preferences and your general health – for instance, your kidney function or the risk of bleeding in your stomach or bowel.

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. The main thing is that you find a medication that works for you, and that you take it every day.

No studies have compared the various direct oral anticoagulants with each other so far. So it isn’t possible to say which of these medications works the best. Initial estimates suggest that apixaban may be a bit more effective than other oral anticoagulants.

When is treatment with anticoagulants recommended?

Whether treatment with medication is a good idea will depend on your individual risk factors for stroke and bleeding, and how you yourself view the pros and cons of the treatment. How long you have had atrial fibrillation generally doesn’t play a role here. 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 make a joint decision.

It isn’t always easy to decide whether or not to have a certain treatment. 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 recalculating your risk of a stroke once every year, and adjusting your treatment if necessary.

Research summaries