Proteolysis of von Willebrand factor and shear stress-induced platelet aggregation in patients with aortic valve stenosis

Background-Excessive bleeding may complicate congenital cardiac defects, To explain the pathogenesis of this abnormality, we evaluated selected parame ters of primary hemostasis in patients with aortic valve stenosis before an d after corrective surgery. Methods and Results-We examined shear-induced platelet aggregation with the filter aggregometer test and von Willebrand factor (vWF) structure by eval uating the multimeric distribution and extent of subunit proteolysis, The p latelet count was reduced before corrective surgery, and shear-induced plat elet aggregation was impaired. Moreover, VWF multimers of higher molecular mass were decreased, and proteolytic subunit fragments were increased. Afte r correction of the cardiac defect, all of these parameters returned to nor mal. Conclusions-Alterations of VWF and platelet function may contribute to the bleeding diathesis in patients with aortic valve stenosis. Improvement afte r corrective surgery suggests that the passage of blood through a stenosed aortic valve may result in shear forces that induce vWF interaction with pl atelets in the circulation and, in turn, trigger platelet clearance, vWF de gradation, and the impairment of primary hemostasis.