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See Also

Peripheral Artery Disease: causes and consequences

Coronary Artery Disease: causes and consequences

An Introduction to
Understanding Thrombosis

This section introduces haemostasis, the coagulation cascade, venous and arterial thrombi and thrombus formation

  • Haemostasis is the normal physiological response preventing significant blood loss after vascular injury
  • The process depends on an intricate series of events involving platelets, other cells, and the activation of specific blood proteins, known as coagulation factors
  • When blood vessel injury occurs, physiological haemostasis is triggered and the coagulation process begins. Haemostasis serves to maintain the integrity of the circulatory system; however, the process can become imbalanced, leading to significant morbidity and mortality
  • Knowledge of the haemostasis process is important in understanding the major disease states associated with thrombosis


Click here to find out more about haemostasis


  • The coagulation process that leads to haemostasis involves a complex set of reactions involving approximately 30 different proteins
  • These reactions convert fibrinogen to fibrin, which, together with platelets, forms a stable thrombus. Several coagulation cascade models have been proposed, including the intrinsic and extrinsic pathway model and the more recent cell-based model
  • Building on these models, research has elucidated a role for other components of the coagulation process, including microparticles and the protein P-selectin
  • An inherited or acquired imbalance in the coagulation system that leads to an increased risk of thrombosis is called thrombophilia
  • Approximately one in three patients with VTE has an inherited thrombophilia

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  • Formation of a thrombus within a vein is known as a venous thrombosis
  • If the thrombus breaks loose and travels through the circulatory system, it is known as an embolus
  • Venous thrombi manifest mainly as DVT and PE
  • DVT is the most common type of VTE, but patients with DVT are also at risk of PE, which can potentially be life-threatening
  • VTE is associated with cancer, trauma and surgery, and several pre-disposing risk factors, including pregnancy, obesity and immobility, have been identified
  • VTE can also lead to serious long-term complications, including PTS and CTEPH

Click here to find out more about venous thrombosis


  • Haemostasis is necessary for survival, but the pathological formation of a thrombus poses significant health risks
  • A pathological thrombus, formed when there is an imbalance in the blood coagulation system, can potentially obstruct blood flow, leading to a number of serious health conditions
  • Two different types of thrombi can be formed:
    • Arterial thrombi
    • Venous thrombi
  • The pathologist Rudolph Virchow postulated that thrombus formation and propagation resulted from abnormalities in three areas, collectively known as Virchow’s triad
  • It is now possible to quantify some of the factors that are associated with an increased risk of VTE and other cardiovascular diseases, and of stroke in patients with AF

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