[The role of thrombotic and hemostatic mechanisms in the initial phases of atherosclerosis].

The factors of thrombosis (endothelium, haemostasis, coagulation, fibrinolysis) are implicated from the initiating phase of atherosclerotic lesions. Their participation is more established (and studied) in the later phases of intraluminal evolution of atherosclerosis, of thromboembolic complications of the lesions and interventional procedures. The traditional theory of response to physical lesions of the endothelium as an initiating factor of atherosclerotic lesions, which gave platelets an essential role, has been replaced by that linking an early functional lesion of the endothelium and a cellular response by monocytes infiltrating the vessel wall, becoming macrophages. The macrophages participate in changes of the LDL in the wall, ingest the lipids at the same time as the smooth muscle cells which have migrated and proliferated from the media to the intima. The lipid overload, especially with oxidised LDL, is intracellular at first in these foam cells, then extracellular as the cells die. During the early stages, all the tissue factors of activation and development of coagulation are present in the vessel wall and then within the lesion. This intra-cellular coagulation results in the production of thrombi in the tissues and the transformation of fibrinogen to fibrin. These stages precede and participate in cellular proliferation and extracellular lipid deposits. Factors of tissular thrombolysis (the uPA pathway) play a part in cellular immigration and proliferation. It is only at a later stage that the lesion activates intravascular coagulation and fibrinolysis which, in conditions of variable equilibrium, will result in the clinical complications of the atherosclerotic process. All these factors therefore participate firstly in the tissues and then within the lumen, in the progression and complications of atherosclerosis which for these reasons is often called atherothrombotic disease. The comprehension of these mechanisms is essential for the development and interpretation of tests and treatment applied to different stages of the disease, which is all the more complex given that in a given patient at a given time, lesions at different stages are present in the arterial network.