Stroke Prevention in Atrial Fibrillation

Atrial fibrillation (AF) is the most common recurrent arrhythmia encountered in clinical practice, and is associated with an overall 5-fold increased risk of stroke and systemic embolism. Oral anticoagulant (OAC) treatment reduces the risk of stroke by 64% and of mortality by 26% when used in patients with non-valvular AF (i.e. AF without moderate-to-severe mitral stenosis or mechanical heart valve).

Despite the proven benefits of OAC therapy, real-world clinical practice suggests a continuing under-use of anticoagulants in AF patients at high risk of stroke. The NHFA/CSANZ Australian Clinical Guidelines for the Diagnosis and Management of AF 2018 highlight the following key points regarding stroke prevention in non-valvular AF.

• OAC therapy should be risk-based and account for stroke and bleeding risk factors as well as the patient’s values and preferences (see Figure).
• To avoid the cumbersome use of different CHA₂DS₂-VASc risk thresholds for males and females when recommending anticoagulation, these guidelines recommend a sexless CHA₂DS₂-VASc score (abbreviated as CHA₂DS₂-VA score).

The CHA₂DS₂-VA score (0 to 8 points) comprises 1-point each for Congestive heart failure, Hypertension, Diabetes, and Vascular disease (i.e. prior myocardial infarction, peripheral arterial disease, or complex aortic atheroma or plaque) and 2 points each for Age >75 years and Stroke history, TIA, or systemic embolism.

• OAC therapy, to prevent stroke:
• Is recommended in men and women with non-valvular AF whose CHA₂DS₂-VA score is 2 or more, unless there are major contraindications to anticoagulation.
• Is not recommended in patients with non-valvular AF whose CHA₂DS₂-VA score is 0.
• Should be considered in patients with non-valvular AF whose CHA₂DS₂-VA score is 1 especially when their bleeding risk is low.
• Modifiable bleeding risk factors should be corrected in patients for whom anticoagulation is indicated. Although patients at high risk of stroke are also at high risk of major bleeding, the net clinical benefit nearly always favours stroke prevention if reversible bleeding factors are corrected.
• Non-vitamin K-dependent oral anticoagulants (NOACs; apixaban, dabigatran or rivaroxaban) are recommended in preference to warfarin when anticoagulation is initiated in a patient with non-valvular AF.
• In addition to the many pragmatic advantages, NOACs are as good as or better than warfarin in reducing stroke, and bleeding rates are similar or less than warfarin (including a significant reduction in risk of intracranial haemorrhage).
• Antiplatelet therapy is not recommended for stroke prevention in non-valvular AF, regardless of stroke risk, since efficacy evidence is weak and aspirin may have similar bleeding rates to OACs.
• Stroke risk may change over time due to ageing or new comorbidities. Hence annual review of low risk patients is recommended to assess stroke risk and the need for anticoagulation.
• Although the risk of dying from AF-related stroke can be largely mitigated by OAC therapy, comorbidities, such as diabetes and heart failure, contribute to increased all-cause deaths in AF patients. To effectively reduce morbidity and mortality, a comprehensive, patient-centred, integrated approach by multidisciplinary teams, is recommended.

References available on request.

Questions? Contact the editor.

Author competing interests: The author acknowledges the assistance of Cia Connell, National Heart Foundation of Australia, in preparing this article.

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