Bayer Pharma AG

Essence of this Article

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 and 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 venous thromboembolism (VTE) and other cardiovascular diseases, and of stroke in patients with atrial fibrillation (AF).

Thrombus Formation

How thrombi develop

A thrombus can block the flow of blood through a vein or artery. If it detaches from the vessel wall and lodges in the lungs or other vital organs, it can become a life-threatening embolus.30, 31 A pathological thrombus forms when there is an imbalance in the blood coagulation system.27

Haemostasis is necessary for survival, but the pathological formation of a thrombus poses significant health risks. The coagulation system depends on a delicate balance between:

  • Natural coagulant and anticoagulant factors
  • The coagulation and fibrinolytic system

An imbalance in these systems can result in pathological coagulation. The resulting thrombus can potentially obstruct blood flow, leading to a number of serious health conditions including heart attacks and cardioembolic stroke in patients with AF, and VTE.30, 32, 33 VTE can manifest as deep vein thrombosis and/or pulmonary embolism – two distinct but related aspects of the same disease.

Virchow’s triad

Virchow’s triad

Virchow's triad

Over 150 years ago, the German pathologist Rudolph Virchow postulated that thrombus formation and propagation resulted from abnormalities in three areas:

  • Blood flow
  • The vessel wall
  • Blood components

These three factors are known as Virchow’s triad.29 The features of this triad have now been further refined:34, 35

  • Blood flow – abnormalities of haemorheology and turbulence at vessel bifurcations and stenotic regions
  • Vessel walls – abnormalities in the endothelium, such as atherosclerosis and associated vascular inflammation
  • Blood components – abnormalities in coagulation and fibrinolytic pathways and in platelet function

Advances in laboratory techniques now enable clinicians to quantify some of these thrombosis-related factors that, when abnormal, confer a ‘prothrombotic’ or ‘hypercoagulable’ state.35

This state is associated with an increased risk of VTE and other cardiovascular diseases – including coronary artery disease and heart failure – and of stroke in patients with AF.35

Two different types of thrombus can form:

  • Arterial thrombus (white thrombus)
  • Venous thrombus (red thrombus)

Arterial and venous thrombi differ in composition and appearance. Arterial thrombi are typically composed mainly of platelet aggregates, giving the appearance of ‘white thrombi’. Venous thrombi largely consist of fibrin and red blood cells so are known as ‘red thrombi’.25


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