Virchow's triad refers to the 3 primary influences for thrombus formation and it includes:
1) Endothelial injury
2) Stasis, turbulence or abnormal blood flow
3) Blood hypercoagulability.
Physical loss of endothelium leads to exposure of subendothelial extra-cellular matrix, adhesion of platelets, release of tissue factor, and local depletion of PGI2 and plasminogen activators.
Abnormal blood flow
Turbulence can cause endothelial injury which is in itself a major influence for thrombosis. Apart from that abnormal blood flow can:
1) Disrupt laminar flow and bring platelets into contact with the endothelium
2) Prevent dilution of activated clotting factors by fresh-flowing blood
3) Retard the inflow of clotting factor inhibitors and permit the buildup of thrombi
4) Promote endothelial cell activation, resulting in local thrombosis, leukocyte adhesion, etc.
It can be primarily due to a genetic disorder and secondarily due to some acquired problems.
The primary causes are:
1) mutation of factor V gene a/k/a factor V Leiden
2) mutation of prothrombin gene
3) anti-thrombin III deficiency
4) protein C deficiency
5) protein S deficiency
The secondary causes are:
1) prolonged immobilization
2) myocardial infarction
3) atrial fibrillation
5) prosthetic cardiac valves
6) heparin induced thrombocytopenia
7) hyperestrogenic states e.g. pregnancy / OCP use
9) sickle cell anemia