Stroke and bleeding risk assessment for atrial fibrillation

Unless patients with atrial fibrillation have a very low stroke risk or an unacceptably high bleeding risk, they should be treated with oral anticoagulant therapy. Oral anticoagulant therapy can prevent most ischaemic strokes, and it is superior to aspirin or no therapy.

Note: Patients with atrial fibrillation should be treated with oral anticoagulant therapy unless they have a very low stroke risk or an unacceptably high bleeding risk.

As soon as atrial fibrillation is diagnosed, assess the patient’s stroke and bleeding risk to determine whether anticoagulation is needed. Patients with atrial fibrillation who have rheumatic mitral stenosis and/or a mechanical heart valve¹ have a particularly increased thromboembolic risk and require anticoagulation (these patients should be treated with warfarin)Connolly, 2022 Hindricks, 2021 NHFA CSANZ Atrial fibrillation guideline working group, 2018. There is no clear evidence that other valvular heart disease (eg mitral regurgitation, bioprosthetic valves) need to be specially considered when assessing stroke risk; patients with these conditions should be assessed and treated as for all other patients with atrial fibrillation (if anticoagulation is indicated, direct-acting oral anticoagulants (DOACs) are usually preferred) Hindricks, 2021 National Institute for Health and Care Excellence (NICE), 2021 Steffel, 2021. For discussion about choice of anticoagulant, see Anticoagulant therapy to prevent thromboembolic events in atrial fibrillation.

Numerous risk scores for bleeding (eg the HAS-BLED score, which includes risk factors such as hypertension, abnormal kidney or liver function, prior stroke, history of bleeding, labile INR, age and other drug or alcohol use) help to determine the harm–benefit balance of anticoagulant therapy and identify potentially correctable bleeding risk factors for patients with atrial fibrillation. However, a high bleeding risk score does not mean that an anticoagulant should not be used; these patients often still have an overall net benefit from anticoagulant therapy based on stroke risk.

Several stroke risk stratification scores are validated for patients with atrial fibrillation. These scoring systems are useful to identify patients at a very low risk of stroke or systemic embolism, in whom anticoagulation may not be required.

The CHA₂DS₂-VASc scoring system to assess stroke risk is widely used; see Clinical risk factors for stroke, transient ischaemic attack and systemic embolism in the CHA2DS2-VASc score. Use of the CHA₂DS₂ score has decreased since the introduction of CHA₂DS₂-VASc; however, at the time of writing, the availability of DOACs on the Pharmaceutical Benefits Scheme (PBS) is determined by a patient’s CHA₂DS₂ score—see the PBS website for current information.

Other stroke risk stratification scores include CHA₂DS₂-VA (used by the National Heart Foundation and the Cardiac Society of Australia and New Zealand at the time of writing), and the Global Anticoagulant Registry in the Field—Atrial Fibrillation score (GARFIELD-AF). CHA₂DS₂-VA does not include female sex as a risk factor. The GARFIELD-AF score is more complex but statistically improves stroke risk prediction; see the GARFIELD-AF Registry website for more informationHindricks, 2021.

When assessing stroke risk, always consider the presence of any additional patient factors that may increase stroke risk but are not covered by the score (eg hypertrophic cardiomyopathy).

Table 1. Clinical risk factors for stroke, transient ischaemic attack and systemic embolism in the CHA₂DS₂-VASc score
CHA₂DS₂-VASc risk factor	Points
congestive heart failure	+1
hypertension	+1
age 75 years or older	+2
diabetes mellitus	+1
previous stroke, transient ischaemic attack or thromboembolism	+2
vascular disease (peripheral artery disease, complex aortic plaque or prior myocardial infarction)	+1
age 65 to 74 years	+1
sex (female) [NB1]	+1
Points for each risk factor are added together to give the score, which is an estimate of thromboembolic risk in patients with atrial fibrillation [NB2].
Note: NB1: Although female sex is a risk factor, it does not increase the stroke risk unless other risk factors are present. NB2: See the MDCalc website for more information on the results of the score.

Most trials evaluating oral anticoagulants in patients with atrial fibrillation have involved patients with a CHA₂DS₂-VASc score of 2 or more. Based on these trials and with consideration of the bleeding riskNational Institute for Health and Care Excellence (NICE), 2021:

for males with a CHA₂DS₂-VASc score of 2 or more and females with a score of 3 or more, strong evidence shows benefit of oral anticoagulant therapy. Give oral anticoagulant therapy to these patients
for males with a CHA₂DS₂-VASc score of 1 and females with a score of 2, evidence for benefit of oral anticoagulant therapy is less strong. Consider oral anticoagulant therapy for these patients
for males with a CHA₂DS₂-VASc score of 0 and females with a score of 1, anticoagulant therapy is not recommended.

Anticoagulant therapy in patients with atrial fibrillation who have palliative care needs can be complex. The decision to continue, change or stop anticoagulation is based on an assessment of expected reduction in risk of stroke or thromboembolism balanced against the elevated risk of bleeding, alongside the potential burden to the patient; see Principles of rationalising anticoagulants in palliative care in the Palliative care guidelines for more information.

¹ The term ‘valvular’ atrial fibrillation has previously been used to describe atrial fibrillation in patients who have rheumatic mitral stenosis and/or a mechanical heart valve—this term should be avoided as it can cause confusionHindricks, 2021.Return