Antithrombotic therapy in atrial fibrillation: aspirin is rarely the right choice

Abstract

Atrial fibrillation, the commonest cardiac arrhythmia, predisposes to thrombus formation and consequently increases risk of ischaemic stroke. Recent years have seen approval of a number of novel oral anticoagulants. Nevertheless, warfarin and aspirin remain the mainstays of therapy. It is widely appreciated that both these agents increase the likelihood of bleeding: there is a popular conception that this risk is greater with warfarin. In fact, well-managed warfarin therapy (INR 2-3) has little effect on bleeding risk and is twice as effective as aspirin at preventing stroke. Patients with atrial fibrillation and a further risk factor for stroke (CHA2DS2-VASc >0) should therefore either receive warfarin or a novel oral agent. The remainder who are at the very lowest risk of stroke are better not prescribed antithrombotic therapy. For stroke prevention in atrial fibrillation; aspirin is rarely the right choice.

Keywords: Anticoagulant; Antithrombotic; Aspirin; Atrial Fibrillation; Warfarin.

Figure 1

Impact of antithrombotic drugs on risk of stroke and major bleeding in patients with non-valvular atrial fibrillation. (A) Relative effects of aspirin and warfarin on risk of stroke and major bleeding. Lines indicate 95% CIs. Asterisks indicate differences which are significant at the 95% confidence level. Adapted from McNamara et al (2004). (B) Impact of international normalised ratio on risk of stroke and intracranial haemorrhage. Illustration based on data from Singer et al (2009).

Figure 2

Variation in stroke risk with CHADS2 score. Bars indicate 95% CIs. Stroke rates are adjusted using a multivariate model to remove the effect of aspirin usage. Note that stroke rates are declining and hence individual values may not reflect the magnitude of stroke risk today. Adapted from Gage et al (2001).³⁵

Figure 3

Algorithm for choosing antithrombotic therapy for stroke prevention in patients with non-valvular atrial fibrillation (AF). Recommendations based on 2010 European Society of Cardiology guidelines—see Camm et al (2010).²⁸ * Aspirin may be considered in these patients, as well as in those with one risk factor for stroke, though it is not the preferred choice. ** While these guidelines were published prior to the formal approval of the new oral anticoagulant agents for stroke prevention in AF, they nevertheless include mention of dabigatran for this indication. *** Or proceed directly to a new oral anticoagulant. INR, international normalised ratio; TIA, transient ischaemic attack.