Secondary prevention of stroke in patients with nonvalvular atrial fibrillation: optimal intensity of anticoagulation.

Nonvalvular atrial fibrillation (NVAF) is frequently seen in elderly people and has become a main cause of cardioembolic stroke. The efficacy of anticoagulation for primary prevention of stroke or transient ischaemic attacks (TIAs) in patients with NVAF has been established by prospective, randomised and controlled trials. Warfarin decreased the frequency of all strokes by 68% and the rate of the combined outcome of stroke, systemic embolism or death by 48%. Anticoagulation with warfarin using international normalised ratios (INRs) ranging from 2.0 to 3.0 is recommended for patients with NVAF, who have any of the risk factors identified by the Atrial Fibrillation Investigators (AFI) [previous stroke or TIA, history of hypertension, diabetes mellitus, advanced age (> or = 65 years old), congestive heart failure and coronary artery disease], the American College of Chest Physicians (ACCP) [increased age (> 75 years old), prior stroke, hypertension and heart failure], or the Stroke Prevention in Atrial Fibrillation (SPAF) investigators [women > 75 years old, prior stroke, systolic blood pressure > 160mm Hg, recent heart failure, and fractional shortening < 25% on echocardiography]. For the secondary prevention of stroke, the efficacy of adjusted-dose warfarin therapy has been demonstrated by 2 major randomised trials. SPAF III (INR 2.0 to 3.0) demonstrated a lower incidence of ischaemic stroke or systemic embolism (3.4 %/year) compared with low fixed-dose warfarin plus aspirin (acetylsalicylic acid) [11.9%]. The European Atrial Fibrillation Trial [EAFT] (INR 2.5 to 4.0) showed a lower incidence of all stroke (4.0 %/year) with adjusted-dose warfarin compared with placebo (12.0 %/year). The incidence of major bleeding in the adjusted-dose warfarin group in SPAF III and EAFT was 2.4 and 2.8 %/year, respectively. EAFT incidence rates for the occurrence of a first ischaemic or haemorrhagic complication analysed by INR range indicated that the rate was lowest at INRs of 2.0 to 2.9, and higher with INRs of 3.0 to 3.9. Therefore, the optimal intensity of anticoagulation for prevention of recurrent stroke seems to be an INR of between 2.0 and 3.0, as for primary prevention. Retrospective and prospective studies from Japan reported that in the elderly, haemorrhagic complications occur frequently with INRs above 2.6 and major ischaemic events cannot be prevented at INRs below 1.6. Therefore, an INR target between 1.6 and 2.6 may be an alternative for secondary prevention of stroke in elderly patients with NVAF who have a potential risk of bleeding, to avoid both major ischaemic and haemorrhagic events. Antiplatelets may be administered in patients who are unable to manage taking warfarin properly or who have a high risk of falling and subsequently sustaining a head injury, although the efficacy of antiplatelets for secondary prevention of stroke in NVAF has not yet been established.