Which patients with paroxysmal or chronic atrial fibrillation should I treat with aspirin, warfarin or neither?

Patients in whom the risk of thromboembolism is considered to be greater than the risk of a serious bleed due to warfarin should be considered for formal anticoagulation. In published clinical trials of anticoagulation the risk of stroke was reduced from 4.3% per year to 1.3% per year with anticoagulation. This equates to 30 strokes prevented for 1000 patients treated with warfarin for 12 months. Whether such benefit can be seen in routine practice depends not only on a careful decision for each patient regarding the risk of bleeding and the risk of thromboembolism, but also on the quality of monitoring the intensity of anticoagulation. The usual practice is to anticoagulate to a target INR of 2.5 (range 2–3), unless there is a history of recurrent thromboemboli in which case higher intensity anticoagulation may be necessary. In the clinical trials the risk of serious bleeding was 0.9% per year in the control group and slightly higher (1.3%) in those on warfarin. Risk factors for bleeding on anticoagulants include serious comorbid disease (such as anaemia, renal, cerebrovascular or liver disease), previous gastrointestinal bleeding, erratic or excessive alcohol misuse, uncontrolled hypertension, immobility, and poor quality clinical and anticoagulant monitoring.

Aspirin therapy is often recommended for elderly patients with atrial fibrillation on the basis that there is a lower risk of bleeding compared with warfarin. The likely benefits of aspirin are also less than those of warfarin. Further, the bulk of AF-associated stroke occurs in those aged >75 years, and the benefits of anticoagulation are not outweighed by the risks in high-risk elderly patients in whom monitoring is carefully carried out.1 Where warfarin is genuinely considered unsuitable (or is unacceptable to a patient), and the patient is at significant risk of thromboembolism, there is evidence that aspirin at a dose of 325mg per day reduces the risk of thromboembolism, but no evidence that lower doses are effective. The combination of fixed-dose low intensity warfarin with aspirin confers no benefit over conventional warfarin therapy in terms of bleeding risks and is less effective in preventing thromboembolism.