In contrast to venous thrombi, which are caused primarily by reduced blood flow and are composed predominantly of fibrin and red cells, arterial thrombi characteristically result from elevated shear stress at sites of vascular injury and are composed predominantly of platelets. Arterial thrombosis is therefore typically caused by abnormalities of platelets and/or the vessel wall. Disorders characterized by a propensity to arterial thrombosis due primarily to abnormalities of platelets include the myeloproliferative disorders, those due to vessel wall abnormalities include homocystinuria and the inflammatory vasculopathies, while those probably due to a combination of platelet and vessel wall abnormalities include heparin-associated thrombocytopenia and thrombosis and the antiphospholipid antibody syndrome.
