The formation of a BLOOD CLOT within the vessels or heart during life. The process of clotting within the body depends upon the same factors as that of clotting of blood outside the body, involving the fibrinogen and calcium salts circulating in the blood, as well as blood PLATELETS. The indirect cause of thrombosis is usually some damage to the smooth lining of the blood vessels brought about by inflammation, or the result of ATHEROMA, a chronic disease of the vessel walls. The blood is also specially prone to clot in certain general conditions such as ANAEMIA, the ill-health of wasting diseases like cancer, and in consequence of the poor circulation of old age as well as periods of immobility, such as during prolonged travel and also in pregnancy. Thrombosis may occur in the vessels of the brain and thus causes STROKE in people whose arteries are much diseased.

Thrombosis of a coronary artery of the heart is a very serious condition which affects, as a rule, middle-aged or elderly people.

(See also ARTERIES, DISEASES OF; COAGULATION; HEART, DISEASES OF – Coronary thrombosis; VEINS, DISEASES OF.)