100 QUESTIONS IN CARDIOLOGY

64 Which patients with paroxysmal or chronic

atrial fibrillation should I treat with aspirin,

warfarin or neither?

Suzanna Hardman and Martin Cowie

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 co-

morbid 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 anti-

coagulation 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 thrombo-

embolism, 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 conven-

tional warfarin therapy in terms of bleeding risks and is less

effective in preventing thromboembolism.