Effects of Fixed Low-Dose Warfarin, Aspirin-Warfarin Combination Therapy, and Dose-Adjusted Warfarin on Thrombogenesis in Chronic Atrial Fibrillation

BACKGROUND AND PURPOSE: Recent clinical trials have established that adjusted-dose warfarin (international normalized ratio INR 2.0 to 3.0) is highly effective in the reduction of ischemic stroke in patients with nonvalvular atrial fibrillation (AF). We hypothesized that the introduction of fixed low-dose warfarin alone or in combination with aspirin (300 mg) could normalize hemostatic markers, namely plasma fibrin D-dimer (an index of thrombogenesis), plasminogen activator inhibitor-1 (PAI-1, an index of fibrinolysis), fibrinogen, and von Willebrand factor (vWf, an index of endothelial dysfunction), in a manner comparable to adjusted-dose warfarin (target INR 2.0 to 3.0). METJODS: Sixty-one patients with AF (44 men, mean+/-SD age 64+/-19 years) who were not receiving any antithrombotic therapy were prospectively randomized into 1 of 3 treatment groups: warfarin (2 mg) (n=23; group 1), combination 1 mg warfarin plus 300 mg aspirin (n=21; group 2) or combination 2 mg warfarin plus 300 mg aspirin (n=17; group 3). Subjects from all 3 AF groups were matched for sex, age, and blood pressure. Blood samples were taken for sequential measurements for changes in plasma fibrin D-dimer, PAI-1, fibrinogen, and vWf before and at 2 and 8 weeks after randomization (phase 1). All patients were subsequently offered adjusted-dose warfarin therapy (phase 2), and an additional blood sample was taken 6 weeks later. RESULTS: When pretreatment results were compared with those from 60 age- and sex-matched healthy control subjects in sinus rhythm, there were significant elevations in levels of fibrinogen (P=0.025), vWf (P<0.0001), and fibrin D-dimer (P<0.0001) in patients with AF compared with control subjects. There were no significant changes in the levels of various indices measured after 2 and 8 weeks of therapy in all 3 groups, except for an increase in PAI-1 level (P=0.024) in group 3. After 6 weeks of therapy with dose-adjusted warfarin (INR 2.0 to 3.0), there was a significant decrease in plasma fibrinogen (P=0.023) and fibrin D-dimer (P=0.0067) levels. There were no significant changes in the levels of PAI-1 (P=0.198) or vWf (P=0.33). CONCLUSIONS: The present results confirmed that high levels of vWf, fibrinogen, and fibrin D-dimer levels were present in patients with AF compared with control subjects. Moreover, the introduction of 300 mg aspirin plus low-dose warfarin (1 mg/d), low-dose warfarin alone (2 mg/d), or 300 mg aspirin plus low-dose warfarin (2 mg/d) did not significantly reduce any of the hemostatic markers studied (except PAI-1 levels), whereas conventional full-dose warfarin (INR 2.0 to 3.0) significantly reduced levels of fibrin D-dimer and fibrinogen. These results are in keeping with the disappointing ineffectiveness of low-intensity warfarin therapy, aspirin-warfarin combination, and ultralow-dose warfarin therapy in the recent prematurely terminated clinical trials and the established benefits of conventional adjusted-dose anticoagulation therapy.