Platelet P-selectin levels in relation to plasma soluble P-selectin and β-thromboglobulin levels in atrial fibrillation

Background and Purpose-The increased risk of stroke and thromboembolism in atrial fibrillation (AF) may be related to a prothrombotic or hypercoagulable state, with abnormalities of hemostasis and platelet activation. To investigate the role of platelets in AF and the influence of antithrombotic therapy, we developed and then applied a new assay to detect the absolute amount of P-selectin per platelet (pP-selectin) based on cell lysis. Thus, pP-selectin in AF patients was compared with that of healthy controls and also with plasma soluble P-selectin (sP-selectin) and beta-thromboglobulin as established indices of platelet activation. Methods-We studied 122 patients (mean [SD] age. 71 [9] years; 65 men) with chronic AF of >6 weeks' duration: 34 were not on antithrombotic therapy, 30 were taking aspirin (75 to 300 mg/d), and 58 were fully anticoagulated with warfarin. pP-selectin was compared with sP-selectin and plasma beta-thromboglobulin levels (enzyme-linked immunosorbent assay). Results were compared with those of 23 healthy controls (mean [SD] age. 74 [9] years; 7 men) in sinus rhythm. Results-pP-selectin was significantly lower in AF patients on no antithrombotic therapy (P=0.03) than in healthy controls, but sP-selectin and beta-thromboglobulin levels were not significantly different and did not differ in patients taking aspirin or warfarin. However, pP-selectin was lower in patients with AF on aspirin than in those on warfarin (P<0.05). pP-selectin/sP-selectin correlated significantly in healthy controls (r=0.47, P=0.03) but inversely (r= -0.43. P=0.03) in AF patients on no antithrombotic therapy. Conclusions-Lower levels of pP-selectin may represent a depletion of pP-selectin after platelet activation in AF. Aspirin further decreases pP-selectin levels compared with warfarin. On the basis of the principle of platelet lysis. we demonstrate that it is possible to determine the amount of P-selectin per platelet, which may be regulated in the megakaryocyte through a cyclooxygenase-dependent pathway.