Thromboprophylaxis for atrial fibrillation

1 - Introduction

This brief overview will address anticoagulant therapy, antiplatelet therapy and where combination therapy may or may not have a role for the prevention of stroke and thromboembolism in patients with atrial fibrillation (AF). 

2 – Anticoagulation therapy is superior to antiplatelet therapy in preventing strokes.

The provision of thromboprophylaxis for AF has many clinical trials to inform an appropriate management strategy.  Generally, anticoagulation therapy reduces strokes by two-thirds compared to control, whilst aspirin reduces stroke by one-fifth [2]. Also, the superiority of anticoagulation therapy (with a 40% risk reduction) over aspirin as thromboprophylaxis in patients with nonvalvular AF is clear [2].  Mortality is not significantly decreased by the use of aspirin compared to placebo in patients with AF.

Aspirin has been used as an alternative to prescribing warfarin, despite the evidence that aspirin is poorly effective for stroke reduction in ‘high risk’ AF patients.  The overall benefit for aspirin in stroke reduction is 22% with fairly wide confidence intervals, almost including unity, indicating no benefit [3].  Of note, aspirin was not beneficial in reducing recurrent strokes or severe strokes.

3 – Warfarin is superior to aspirin for primary stroke prevention in the elderly.

In the recently presented Birmingham Atrial Fibrillation Treatment of the Aged (BAFTA), anticoagulation with warfarin was superior to aspirin for primary stroke prevention amongst elderly patients (age>75 years) with AF, in the primary care setting [4].  The BAFTA trial showed that warfarin was very effective thromboprophylaxis in the elderly, with no significant increased bleeding risk with age.  Thus, there is a very strong argument to use warfarin more often in elderly patients.

4 - AF commonly coexists with vascular disease, the effect of antiplatelet therapy [or aspirin alone] in AF is probably the effect on vascular disease.

What is less well known is that the perceived overall stroke reduction benefit of aspirin (by approximately one-fifth) in AF is largely driven by one clinical trial—the first Stroke Prevention in Atrial Fibrillation (SPAF-I) Trial which had a degree of internal inconsistency in the aspirin effect within the study itself [5]. As AF commonly coexists with vascular disease, the effect of antiplatelet therapy [or aspirin alone] in AF is probably the effect on vascular disease, rather than on the stroke associated with AF per se – indeed, antiplatelet therapy compared to control in ‘high risk’ vascular disease patients also reduces stroke by 22% [6].

5 – Antiplatelet therapy is relatively inefficacious in high risk patients with AF. 

The relative inefficacy of aspirin (and antiplatelet therapy) in high risk patients with AF is also clearly evident from other studies [7,8].  One recent clinical trial, the ACTIVE-W trial [8] of moderate to high risk patients with AF randomized patients to warfarin or combination antiplatelet therapy of aspirin/clopidogrel.  This trial was stopped early due to the inferiority of aspirin/clopidogrel combination therapy vs anticoagulant therapy for the composite endpoint of stroke, embolism, or vascular death, with no significant difference in bleeding rates [8].   

6 – Evidence for aspirin use is weak in “low risk” patients with AF.

Even in ‘low risk’ patients with AF, the evidence for aspirin use is pretty weak. In the Japanese AF Stroke Trial [9], which was performed in low risk patients with AF, there was no significant difference in primary endpoint rate between aspirin or placebo.

7 – Combining aspirin with anticoagulation therapy  (combination therapy ) increases bleeding risk.

The data combining aspirin with anticoagulant therapy also shows little evidence for additive benefit for stroke prevention but a substantial increase in bleeding rate by using such combination therapy [10].   In a more recent analysis [11], there was again no significant additive effect of aspirin to anticoagulant therapy in stroke prevention or the reduction in vascular events (including death or myocardial infarction) but instead, combining aspirin with anticoagulants resulted in a substantial increase in bleeding risk. 

8 – Combination therapy in the setting of AF plus percutaneous coronary intervention and/or stents and/or acute coronary syndrome can be useful.

Perhaps the one situation where we might need combination therapy with anticoagulant plus antiplatelet therapy is in the setting of AF plus percutaneous coronary intervention and/or stents and/or acute coronary syndrome [12].  Here cardiologists have to balance the risk of stroke in AF versus the prevention of recurrent cardiac ischemic events in the acute coronary syndrome setting, against the bleeding risks associated with combination ‘triple antithrombotic therapies’.  

 The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.