Oral Anticoagulants Top Antiplatelet Drugs for Stroke Prevention in A-Fib

ROCHESTER, Minn., July 18 -- Patients with nonvalvular atrial fibrillation have about a 33% lower risk of stroke and major vascular events when treated with oral anticoagulants rather than antiplatelet therapy, findings from a systematic review of clinical trials suggest.

The magnitude of the advantage ranged from 29% for disabling or fatal strokes to 52% for systemic emboli. The two types of therapy had equivalent effects on vascular death and all-cause mortality, according to a review published online in issue 3 of The Cochrane Library.

The reduction in clinical events with oral anticoagulants came at a price, however: a doubling of the risk of intracranial hemorrhage compared with the risk from antiplatelet drugs, reported Maria Aguilar, M.D., of the Mayo Clinic, and colleagues.

Despite the advantages demonstrated by the review, physicians should use a risk-adjusted strategy for clinical decision-making about anticoagulants, the researchers said.

"The threshold of benefit that would warrant anticoagulation remains controversial and depends on patient preferences and availability of optimal anticoagulation monitoring," Dr. Aguilar and colleagues concluded.

"In most cohorts of [atrial fibrillation] patients without prior stroke or TIA, about 40% have a sufficiently low stroke rate during antiplatelet therapy that the absolute benefits of oral anticoagulants would be small (below 1% per year)."

The review was undertaken because of uncertainty surrounding the suspected cardioembolic nature of most strokes in atrial fibrillation patients. Oral anticoagulants and antiplatelet agents have demonstrated stroke prevention efficacy in high-risk patients, however, primary prevention in patients with non-valvular atrial fibrillation merited separate consideration, the authors stated.

A search of the Cochrane databases, published literature, and information on published clinical studies yielded eight randomized trials that involved a total of 9,598 patients treated with adjusted dose warfarin or aspirin in doses ranging from 75 to 325 mg/day. All of the trials limited enrollment to patients who had no history of stroke or TIA. Follow-up averaged 1.9 years.

As compared with aspirin, oral anticoagulants significantly reduced the risk of:

• All stroke (odds ratio 0.68)
• Ischemic stroke (OR 0.53 ), and
• Systemic emboli (OR 0.48)

Treatment with oral anticoagulants versus aspirin also led to nonsignificant reductions in disabling or fatal strokes (OR 0.71) and myocardial infarction (OR 0.69). Vascular death (OR 0.93) and all-cause mortality (0.99) were similar with the two prevention strategies.

Oral anticoagulants were associated with a statistically significant increased risk of intracranial hemorrhage (OR 1.98) compared with aspirin. However, the authors noted, CNS bleeding occurred infrequently with either type of therapy.

For primary prevention of stroke in patients with atrial fibrillation, the absolute benefit of oral anticoagulants versus antiplatelet therapy is modest, Dr. Aguilar and co-authors stated. In the clinical arena of secondary prevention, oral anticoagulants continue to offer larger absolute benefits.