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Atrial Fibrillation and Warfarin

If you have atrial fibrillation (AF), you may be advised to take warfarin to reduce your risk of having a stroke.

What is atrial fibrillation?

Another post discusses atrial fibrillation (AF) in more detail. Briefly, AF means the heartbeat is fast and erratic. Initial treatment is to bring the heart rate down to normal to control symptoms. However, the heart rhythm remains erratic which sometimes leads to the complication of a stroke.

Why is a stroke a possible complication of atrial fibrillation?

In AF there is turbulent blood flow in the heart chambers caused by the erratic heartbeat. This sometimes leads to a small blood clot forming in a heart chamber. A small blood clot can travel in the blood vessels until it gets stuck in a smaller blood vessel in the brain. Part of the blood supply to the brain may then be cut off, which causes a stroke. The risk of having a stroke varies depending on the cause of AF, age, and other 'risk factors'.

  • The risk is highest in people who have damaged heart valves from rheumatic fever and AF.

  • People with AF over the age of 65, or younger people with certain 'risk factors', have a medium risk. Without treatment, this is about a 1 in 20 chance of having a stroke per year.

  • Risk factors are: heart failure, diabetes, high blood pressure, a history of blood clots.

  • People with AF under the age of 65 with no 'risk factors' have a low risk of stroke.

What does warfarin do?

Warfarin works by reducing some of the chemicals in the blood that are needed to make blood clot. This is known as anticoagulation. Recent studies which looked at people with AF have shown that by taking warfarin the risk of having a stroke is reduced. For every 1000 people with AF who take warfarin, about 25-30 strokes per year will be prevented.

Are there any risks with warfarin treatment?

As with all treatments, there is a small risk if you take warfarin. The main risk is that a bleeding problem may develop as the blood will not clot so well. For every 1000 people with AF who take warfarin, 3 are likely to have a serious bleeding problem from the treatment. For example, you could develop a bleeding ulcer in your intestines (guts), or suffer a stroke. (This would be the less common form of stroke due to bleeding into part of the brain and not due to a blood clot.)

Most people with AF who have a medium or high risk of having a stroke are advised to take warfarin. However, it is a joint decision between you and your doctor. It will involve weighing up the risks of developing a stroke against the small risk of a complication from the warfarin treatment.

What does warfarin treatment involve?

You will need regular blood tests to check on how quickly your blood clots when you are taking warfarin. Blood tests may be needed quite often at first, but should reduce in frequency 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. Your doctor will advise you on how to take warfarin, and if it affects any other medication that you take.

Warfarin can interact with some other medications:

Increased warfarin effect: some antibiotics, alcohol, amiodarone, anti-inflammatory painkillers.

Reduced warfarin effect: some anti-convulsant medications, some antituberculosis antibiotics, alcohol.


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