Warfarin reduces the risk of people with atrial fibrillation (AF) having a stroke.
What is atrial fibrillation?
Another leaflet discusses atrial fibrillation (AF) in more detail.
Briefly, people with untreated AF have a heartbeat that is fast and
erratic. Treatment in most cases is to bring the heart rate down to
normal. This usually eases most symptoms. However, in many cases the
heart rhythm remains erratic even if the rate is brought down
to normal. It is this erratic rhythm of the heartbeat that sometimes
leads to the complication of a stroke.
Why is a stroke a possible complication of atrial fibrillation?
The erratic heart rhythm of AF causes turbulent blood flow within the heart chambers. This sometimes
leads to a small blood clot forming in a heart chamber. A clot can then
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. Therefore, the main complication of AF is an increased risk of
having a stroke.
The risk of developing a blood clot and having
a stroke varies, depending on various factors. The level of risk is
divided into three categories: high, medium and low risk.
-
High risk
means that, without treatment, you have about a 6-12 in 100 chance
(sometimes higher) of having a stroke in the next year. People in the
high risk group include those:
- who have already had a stroke or known blood clot, or
- are aged 75 years or older who also have one of the following 'risk
factors': high blood pressure, diabetes or a cardiovascular disease
(such as angina, heart attack, peripheral vascular disease), or
- who have a heart valve problem, or
- who have heart failure or poor heart function shown on a heart scan.
-
Moderate risk means that you have about a 3-5 in
100 chance of having a stroke in the next year. People in the moderate
risk group include those:
- aged 65 years or older (with no high risk factors), or
- who are of any age (up to age 75 when the risk is high) but who
also have one of the following 'risk factors': high blood pressure,
diabetes or a cardiovascular disease (such as angina, heart attack,
peripheral vascular disease).
-
Low risk means that you have about a 1-2 in 100
chance or less of having a stroke in the next year. People in the low
risk group are all people with AF aged less than 65 and who do not have
any risk factors that put them in the high or moderate risk category.
What does warfarin do and how effective is it?
Warfarin interferes with certain chemicals in the blood to prevent
blood clots forming so easily. This is known as anticoagulation. Some
people call anticoagulation 'thinning the blood' although the blood is
not actually made any thinner. Warfarin is the most commonly used
anticoagulant drug. Recent studies which looked at people with AF have
shown that by taking warfarin the risk of having a stroke is greatly
reduced.
Overall, warfarin reduces the risk of stroke by
nearly two-thirds. In other words, warfarin treatment can prevent about
6 in 10 strokes that would have occured in people with AF. The greatest
benefit is seen in those people who are in the 'high risk' category of
having a stroke (described above). For example:
- For people
with AF who are at high risk of stroke, about 80-90 strokes will be
prevented each year for every thousand people treated with warfarin.
- For people with AF who are at moderate risk of stroke, about 25
strokes will be prevented each year for every thousand people treated
with warfarin.
Are there any risks with taking warfarin?
As with most treatments, there is some 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 thousand people with AF who take warfarin,
about nine people per year 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 bleed into the brain (a
cerebral haemorrhage). If you have a serious bleed you are likely to
need to be admitted to hospital, often needing a blood transfusion, and
it can even result in death.
Most people with AF who have a high
or medium risk of having a stroke are advised to take warfarin.
However, some people with a moderate risk may be treated with aspirin
rather than warfarin (see below), particularly if the risks of taking
warfarin are higher than average. People with a low risk of having a
stroke are not usually advised to take warfarin. This is because the
benefit does not usually outweigh the risk of serious bleeding problems
with taking warfarin. In short, the decision to take warfarin is a
joint decision between you and your doctor. It involves weighing up the
risk of having a stroke against the small risk of a complication from
taking warfarin.
Aspirin is another drug that helps to prevent
blood clots forming. It is not as effective as warfarin, but is less
likely to cause serious problems. It is usually advised if you only
have a low risk of stroke, or if you cannot take warfarin or do not
wish to take warfarin.
What does warfarin treatment involve?
Most people who take warfarin attend a 'warfarin
clinic'. This may be at your GP practice, or at the local hospital. The
clinic is run by a health professional specially trained in
anticoagulation. He or she may be a doctor, specialist nurse, trained
pharmacist, etc.
You will need regular blood tests to check on
how quickly your blood clots when you are taking warfarin. Blood tests
(and clinic visits) 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.
You will be
advised on how to take warfarin, and if it affects any other medication
that you take. For example, the following are commonly advised:
- You should aim to take warfarin at the same time each day.
- If you accidentally miss a dose, NEVER take a double dose 'to
catch up' (unless specifically advised by a doctor or by the person who
runs the warfarin clinic).
- Seek advice promptly if you think that you have taken too much warfarin by mistake, or have missed any doses.
Other medication whilst taking warfarin
If
you are prescribed or buy any other drug then tell a doctor, nurse or
pharmacist that you are on warfarin. This is because some drugs
interfere with the way warfarin works and your dose of warfarin may
need to be altered. Also, if you stop another drug or change the dose,
seek advice from a doctor or nurse as your dose of warfarin may need to
be altered.
Diet
If you have a major change in your diet
or the foods that you eat then seek advice from the warfarin clinic. A
major change in diet may mean that you need more closer monitoring and
may need a change in warfarin dose. In particular, if you eat a vitamin
K-rich diet you should not change your eating habits without at the
same time reducing the dose of warfarin. Two other commonly eaten foods
that are known to interact with warfarin are cranberry and grapefruit.
To make things easier, it is probably best simply to avoid foods that
contain cranberry or grapefruit.
Women of childbearing age
Seek advice
promptly if you become pregnant or are planning a pregnancy. For safety
reasons warfarin is likely to be stopped and an alternative drug called
heparin is likely to be used instead.
What if I bleed whilst taking warfarin?
An indication that the dose of warfarin is too high is that you may
bleed or bruise easily. Also, if you bleed, the bleeding may not stop
as quickly as normally. For example, you may have: bleeding gums;
nosebleeds; prolonged bleeding from cuts; blood in the urine.
If
you cut yourself, or have any other bleeding, seek medical help as soon
as possible if the bleeding does not stop as quickly as you would
expect. If you injure an arm or leg which is bleeding, until you get
medical help then ideally keep the affected part raised above the level
of your heart. If you vomit blood, get medical help immediately - ring
for an ambulance.
Some other general points about taking warfarin
- Always carry with you the yellow anticoagulant treatment
booklet which will be given to you. This is in case of emergencies and
a doctor needs to know that you are on warfarin, and at what dose.
- If you have surgery or an invasive test, you may need to temporarily stop taking warfarin.
- Tell your dentist that you take warfarin. Most dental work does not
carry a risk of uncontrollable bleeding. However, for dental
extractions and surgery you may need to temporarily stop taking
warfarin.
- You should limit the amount of alcohol that you drink to a maximum of one or two units a day, and never binge drink.
- One unit of alcohol is about equal to:
- half a pint of ordinary strength beer or lager (3-4% alcohol by volume), or
- a small pub measure (25 ml) of spirits (40% alcohol by volume), or
- a standard pub measure (50 ml) of fortified wine such as sherry or port (20% alcohol by volume).
- There are one and a half units of alcohol in:
- a small glass (125 ml) of ordinary strength wine (12% alcohol by volume), or
- a standard pub measure (35 ml) of spirits (40% alcohol by volume).
- Ideally, try to avoid activities that may cause abrasion,
bruising, or cuts (for example, contact sports). Even gardening,
sewing, etc, can put you at risk of cuts. Do be careful and wear
protection such as proper gardening gloves when gardening.
- Take extra care when brushing teeth or shaving to avoid cuts and
bleeding gums. Consider using a soft toothbrush and an electric razor.
- Try to avoid insect bites. Use a repellent when you are in contact with insects.
Further help and advice
British Heart Foundation
14 Fitzhardinge Street, London, W1H 6DH
Tel (Heart Help Line): 08450 70 80 70 Web: www.bhf.org.uk
Anticoagulation Europe
PO Box 405, Bromley, Kent, BR2 9WP
Tel: 020 8289 6875
Web: www.anticoagulationeurope.org
A charity providing information and advice to people on oral anticoagulation treatment.
References
© EMIS and PiP 2008 Updated: 17 Mar 2008
