Effects of Fixed Low-Dose Warfarin, Aspirin-Warfarin Combination Therapy, and Dose-Adjusted Warfarin on Thrombogenesis in Chronic Atrial Fibrillation
Authors: Li-Saw-Hee Foo Leong , Blann Andrew D. , Lip Gregory Y. H. 
Published: June 2011

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).

Methods
—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.