Thrombosis

Thrombosis is the abnormal formation of a blood clot, or thrombus, inside an unbroken blood vessel or a chamber of the heart. A thrombus has the same ingredients as an ordinary clot, platelets bound together in a mesh of the protein fibrin, but it forms where there is no bleeding to stop. It may cling to the vessel wall and partly narrow it (a mural thrombus) or plug the vessel completely (an occlusive thrombus).

Three kinds of problem favor thrombosis: damage to the inner lining of a vessel, slow or stagnant blood flow, and blood that clots too easily, as in inherited clotting disorders. In arteries, thrombi usually form on atherosclerotic plaques and can cause heart attacks and strokes. In veins, they often form in the deep veins of the leg or pelvis after surgery, injury or long periods without moving, a condition called deep vein thrombosis (DVT).

The greatest danger is that part of a thrombus breaks loose and travels as an embolus. A clot from a leg vein can lodge in the lungs as a pulmonary embolism, which can be fatal. Thrombosis is prevented and treated with anticoagulants such as heparin, antiplatelet drugs such as aspirin, and clot-dissolving drugs.