Can we predict stroke in atrial fibrillation?

Abstract

Stroke prevention with appropriate thromboprophylaxis still remains central to the management of atrial fibrillation (AF). Nonetheless, stroke risk in AF is not homogeneous, but despite stroke risk in AF being a continuum, prior stroke risk stratification schema have been used to 'artificially' categorise patients into low, moderate and high risk stroke strata, so that the patients at highest risk can be identified for warfarin therapy. Data from recent large cohort studies show that by being more inclusive, rather than exclusive, of common stroke risk factors in the assessment of the risk for stroke and thromboembolism in AF patients, we can be so much better in assessing stroke risk, and in optimising thromboprophylaxis with the resultant reduction in stroke and mortality. Thus, there has been a recent paradigm shift towards getting better at identifying the 'truly low risk' patients with AF who do not even need antithrombotic therapy, whilst those with one or more stroke risk factors can be treated with oral anticoagulation, whether as well-controlled warfarin or one or the new oral anticoagulant drugs. The new European guidelines on AF have evolved to deemphasise the artificial low/moderate/high risk strata (as they were not very predictive of thromboembolism, anyway) and stressed a risk factor based approach (within the CHA(2) DS(2)-VASc score) given that stroke risk is a continuum. Those categorised as 'low risk' using the CHA(2) DS(2)-VASc score are 'truly low risk' for thromboembolism, and the CHA(2) DS(2)-VASc score performs as good as-and possibly better--than the CHADS(2) score in predicting those at 'high risk'. Indeed, those patients with a CHA(2) DS(2)-VASc score = 0 are 'truly low risk' so that no antithrombotic therapy is preferred, whilst in those with a CHA(2) DS(2)-VASc score of 1 or more, oral anticoagulation is recommended or preferred. Given that guidelines should be applicable for >80% of the time, for >80% of the patients, this stroke risk assessment approach covers the majority of the patients we commonly seen in everyday clinical practice, and considers the common stroke risk factors seen in these patients. The European guidelines also do stress that antithrombotic therapy is necessary in all patients with AF unless they are age <65 years and truly low risk. Indeed, some patients with 'female gender' only as a single risk factor (but still CHA(2) DS(2)-VASc score of 1, due to gender) do not need anticoagulation, especially if they fulfil the criterion of "age <65 and lone AF, and very low risk". In the European and Canadian guidelines, bleeding risk assessment is also emphasised, and the simple validated HAS-BLED score is recommended. A HAS-BLED score of ≥ 3 represents a sufficiently high risk such that caution and/or regular review of a patient is needed. It also makes the clinician think of correctable common bleeding risk factors, and the availability of such a score allows an informed assessment of bleeding risk in AF patients, when antithrombotic therapy is being initiated.