Atrial fibrillation (AF) causes a fast and erratic heartbeat. Medicines can be used to control the heart rate but AF can also cause blood clots to form in the heart. A blood clot may travel to the brain and cause a stroke. A medicine to prevent clots forming is usually advised for people with AF to reduce the risk of having a stroke.
Why does atrial fibrillation increase your risk of suffering a stroke?
The main complication of atrial fibrillation (AF) is an increased risk of having a stroke. AF can interfere with the blood flow in the heart chambers. This sometimes leads to a small blood clot forming in a heart chamber.
A clot can travel in the blood vessels until it gets stuck in a smaller blood vessel in the brain (or sometimes in another part of the body). Part of the blood supply to the brain may then be cut off, which causes a stroke.
The risk of developing a blood clot and having a stroke varies, depending on several factors. The level of risk can be calculated by your doctor using a set of specific questions. This will help to decide what treatments are required. All people except those at the lowest risk will be offered medication to help prevent clots from forming.
How can the risk of stroke be reduced?
Medicines called anticoagulants can be used to reduce the risk of a blood clot and so reduce the risk of stroke. Anticoagulants work by prolonging the time it takes for blood to form a clot. Some people call anticoagulation "thinning the blood" although the blood is not actually made any thinner.
Anticoagulants reduce the risk of stroke by nearly two thirds. In other words, these treatments can prevent about 6 out of 10 strokes that would have occurred in people with AF.
Should you take medicine to reduce your risk of stroke?
Your doctor can use a risk assessment to see if you should take medicine to reduce your risk of stroke. The most commonly used risk assessment tool is called the CHADS2 risk score. Points are added for each of the following it they apply to you:
- Congestive heart failure with a recent exacerbation (1 point)
- Hypertension - past or present (1 point)
- Aged 75 years or older (1 point)
- Diabetes (1 point)
- Past history of a stroke or transient ischaemic attack (2 points)
If you score 1 or more points then the risk of stroke outweighs any risk from taking the medicine.
The CHADS2-VASc score is also sometimes used. This is an extension of the CHADS2 score. The CHADS2-VASc score uses additional stroke risk factors to help decide whether or not you should be taking an anticoagulant medicine.
Which medicines help to reduce the risk of stroke?
The medicines used to prevent a stroke are called anticoagulants. These help to stop blood clots forming in your blood vessels. By far the most commonly used medicine is warfarin. Aspirin is no longer recommended for stroke prevention in people with atrial fibrillation because it is not very effective.
There are also new medicines that are as effective as warfarin and may have some advantages. These medicines are dabigatran, apixaban and rivaroxaban. The National Institute for Health and Care Excellence (NICE) has recommended that any of these newer medicines can be used to reduce the risk of stroke in patients with AF.
Warfarin can interact with some foods, alcohol and other medicines. Some of the newer anticoagulants (dabigatran, apixaban and rivaroxaban) have less interaction with foods, alcohol and other medicines.
If you take warfarin you will need regular blood tests (INR tests) to check how quickly your blood clots. Blood tests may be needed quite often at first, but should become less often quite quickly. The aim is to get the dose of warfarin just right so your blood does not clot as easily as normal, but not so much as to cause bleeding problems. Dabigatran, apixaban and rivaroxaban do not need regular blood tests.
What are the benefits and risks of anticoagulant medicines?
The benefit of taking warfarin or one of the newer medicines recommended by NICE is to reduce your risk of stroke. The main side-effect of these medicines is an increased risk of serious bleeding.
Taking warfarin has a risk of bleeding and the dose of warfarin needs to be checked regularly. Therefore you will need to have regular blood tests if you are taking warfarin. If severe bleeding does happen, an injection of vitamin K will help to stop the effect of warfarin and so help to stop the bleeding.
The newer medicines (dabigatran, apixaban and rivaroxaban) also increase the risk of bleeding but you will not need to have regular blood tests. Apixaban and rivaroxaban currently have no treatment to stop the effect of these medicines if you do have severe bleeding. Dabigatran can be reversed quickly with Idarucizumab (Praxbind). However Apixaban and rivaroxaban do not stay in your body as long as warfarin does. This mean that any problem with bleeding disappears more quickly. Usually in 12-24 hours.
Warfarin is still considered the first choice of medicine for most people. This is partly because of cost but also because warfarin has been used for a long time. This means that much more is known about the benefits and risks of warfarin compared with the newer medicines.
An operation can be used to reduce the risk of stroke for people with AF. The operation is called left atrial appendage occlusion and closes a pouch in the heart, called the left atrial appendage.
This operation is not widely available in the UK. However NICE has recommended that left atrial appendage occlusion can be considered as a treatment option to reduce the risk of stroke in people with AF.
Dr Colin Tidy
Dr Colin Tidy
Dr Hayley Willacy