Patients with atrial fibrillation (AF) over the age of 85 and those with a previous history of ischaemic stroke derive the greatest net benefit from warfarin, a large observational cohort study has shown.

In the ATRIA trial, 13,000 patients with non-valvular AF were followed up for six years, with more than 1,000 ischaemic strokes and several hundred intracranial haemorrhages recorded.

The net clinical effect of warfarin was defined as the reduction in ischaemic stroke and systemic embolism balanced against the increase in intracranial haemorrhage.

The risk of haemorrhage was further weighted by a factor of 1.5 because of the severity of the health consequences of such bleeds. However, extracranial bleeds were excluded as 90% of deaths attributed to warfarin involve intracranial bleeds. This of course could have resulted in an overestimation of the benefits of warfarin.

The results showed that the patients with the greatest net benefit from warfarin had a previous history of ischaemic stroke, NNT for one year to prevent one ischaemic stroke = 40, or were older than 85, NNT= 43.

The absolute risk of intracranial haemorrhage caused by warfarin was relatively static across the thromboembolic risk groups. The CHADS2 stroke risk score gives 1 point for each of congestive heart failure, hypertension, age, and diabetes and 2 points for stroke. This risk score correctly identified those who would benefit from warfarin treatment with patients scoring 0 or 1 gaining no benefit from warfarin whereas those with a score of 2 or greater did benefit.

The authors commented that the quality of anticoagulation control was important and suggested a minimal standard of an INR in the 2-3 range for 60% or more of the time.

Atrial fibrillation is a growing problem both in terms of timely identification and appropriate intervention. One of the key components of managing AF is the introduction of appropriate thromboprophylaxis. Several scoring systems exist to inform this decision at the core of which lies the need to reduce the risk of thromboembolic stroke while minimising the risk of bleeding from both intra- and extracranial sites.

Therefore, this study further reinforces the message that age should not be a barrier to warfarin use and that older patients have the most to gain from anticoagulation. It also shows that the CHADS2 scoring system is not only simple to apply but an accurate predictor of stroke risk.

However, not all elderly patients will be candidates for warfarin and it is still important to make a clinical judgment as to the risks and benefits in each individual patient.