One in every four deaths is due to thrombosis . This thrombosis occurs in the arterial system as myocardial infarction and stroke, but also often in the venous system in the form of deep vein thrombosis or pulmonary embolism, collectively termed venous thromboembolism (VTE). The annual frequency of VTE is 1-2 per 1,000 per year . The incidence has a very steep age gradient such that the young are rarely affected, whereas it is very common in the old, in particular in combination with co-morbidities such as chronic inflammatory disease and cancer.
The mechanistic framework that helps to understand and explain the causes of VTE is based on Virchow’s triad . This triad postulates that blood flow, the state of the vessel wall and the composition of the blood represent the three main determinants of whether a thrombotic event will occur or not. In arterial thrombosis the state of the vessel wall is the strongest determinant, whereas in venous thrombosis it is the composition of the blood.