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stroke risk and anticoagulation

Atrial fibrillation (AF)

Stroke risk and anticoagulation

During atrial fibrillation, the risk of stroke increases because the atria do not contract / pump normally, which means the flow of blood is slowed. 

This can cause blood inside the heart to pool, which may cause a thrombus (clot ) to form. If the blood clot leaves the heart it can travel to any part of the body, such as the brain resulting in a stroke.

Research has shown that strokes caused by AF are often more severe than non AF-related strokes.

If you have AF, you are at increased risk of a stroke compared to someone who does not have AF. 

We will assess your risk of stroke by using an international scoring system, called the CHA2DS2VASc score. This looks at other conditions that also increase your risk of stroke, such as diabetes. 

 Congestive heart failure
 Hypertension  1
 Age (>75yrs)
 Diabetic  1
 Stroke or TIA
 Vascular heart disease
 Age (65-74 years)
 Sex (female)

Each condition is given a score of either 1 or 2. 

You will be given a score of 0 if you do not have any of the above risk factors, which is considered low risk (less than 1 per cent risk of stroke per year) and an anticoagulant is not needed. 

A score of 1 is considered moderate risk and an anticoagulant (such as warfarin or one of the newer anticoagulants) may be recommended. Anticoagulants are effective at reducing the risk of thrombus by around 50-60 per cent. 

Previously, moderate risk patients were offered antiplatelet drugs, such as aspirin and clopidogrel. However, recent research has shown that antiplatelets are ineffective in reducing the risk of stroke while increasing the risk of bleeding. 

A score of 2 or greater is considered as high risk of having a stroke and an anticoagulant is usually recommended.

The table below shows your stroke risk percentage per year according to your CHADSVASC score. For example, if you have a CHADSVASc score of 2 you have a 2.2 per cent per annum risk of having a stroke without anticoagulation. Therefore, two people in every 100 people over a year will have a stroke.

 CHADSVASc score  Annual stroke risk percentage

Bleeding risk

Although anticoagulants can reduce the presence of clots and risk of stroke, they can increase the risk of bleeding. It is therefore important that both your stroke risk and bleeding risk are assessed to determine whether an anticoagulant would provide more benefits than risks.

To help identify people at a high risk of bleeding, we use another scoring system called HAS-BLED.

 Hypertension (uncontrolled BP, systolic >160 mmhg)
 Abnormal renal or liver function
 1 or 2
 Bleeding  1
 Labile INR (<60 per cent in range)
 Drugs or alcohol
 1 or 2

A score above 3 is considered high risk for bleeding and needs to be carefully monitored. It does not necessarily mean that you will not be prescribed an anticoagulant as the risk of having a stroke may still be higher than the risk of bleeding. 

The healthcare professional will discuss this with you and will also address factors that could be corrected, such as controlling blood pressure.

Read more about anticoagulant medications:


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