Platelet Activation Is Not Involved in Acceleration of the Coagulation System in Acute Cardioembolic Stroke With Nonvalvular Atrial Fibrillation

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Abstract
Background and Purpose It is generally accepted that the coagulation system is activated in ischemic stroke and that platelet activation is involved in the pathogenesis of this disease. However, little is known about how and to what extent platelet activity participates in coagulation system enhancement. We evaluated the hemostatic condition, especially with regard to platelet function and the coagulation system, within 3 days of onset of acute stroke. The study participants were limited to elderly patients with cardioembolic stroke due to nonvalvular atrial fibrillation. Methods Seventeen elderly patients with acute cardioembolic stroke due to nonvalvular atrial fibrillation were investigated. Within 3 days of stroke onset, β-thromboglobulin (BTG), platelet factor 4 (PF4), thrombin-antithrombin III complex (TAT), and d- dimer from arterial blood were carefully evaluated in these patients. Blood samples from 19 healthy age- and sex-matched control subjects were also examined. Results The two studied markers of platelet activity did not change in the patients or the control subjects, and the between-group differences between the stroke and control groups were not statistically significant (BTG, 43.8 versus 31.9 ng/mL; PF4, 9.06 versus 5.78 ng/mL; respectively). In contrast, the two studied coagulation-system indicators were markedly elevated in the patients compared with the control subjects (TAT, 13.8 versus 3.5 ng/mL, P <.01; d- dimer, 366.3 versus 147.2 ng/mL, P <.01; respectively). Conclusions Platelet function was not enhanced in the acute stage of cardioembolic stroke with nonvalvular atrial fibrillation. This result indicates that enhancement of the coagulation system in cardioembolic stroke is not the result of platelet hyperfunction, ie, “platelet-fibrin” thrombi, but rather of “stasis-related” thrombi formation.