Anticoagulants, Antithrombotic and Thrombolytic Agents

Abstract

Thrombi are blood clots that form within the blood stream. Their presence is always pathologic. They can cause disease locally or can break loose (embolize) and lodge downstream, causing major damage distant from their site of origin. Because of the difference in patterns of blood flow in arteries and veins (rapid and high pressure in arteries, slow and low pressure in veins), the thrombi that form in these two sites are structurally different (Freiman 1987). Venous clots consist largely of red cells held together by a network of fibrin. They form in areas of stagnant blood, often starting in the pocket of a valve cusp, especially in the legs, where clotting can proceed undisturbed. Once begun, extension of the clot can be remarkably rapid. A thrombus beginning in the deep veins of the calf can extend within a day to the upper thigh, although many will remain localized. These restricted clots may produce local symptoms of pain, tenderness, heat, and swelling or may cause no symptoms at all. The first indication of a clot in the deep veins of legs or pelvis may be the occurrence of pulmonary embolus.