3 Conditions to Form Thrombus

Thrombus are the pathological formation of intravascular blood clots that are attached to the vessel wall (If it’s not attached, it could be an embolus!). This can either be in an artery or a vein, each leading to different complications. The most common type of thrombus is a Deep Vein Thrombus (DVT) in the leg below the knee.

Cause of a thrombus:

The causes closely relate to Virchow’s triad

  1. Disruption of normal blood flow:

Normal blood flow is expected to be linear and non-turbulent. When blood stops flowing (stasis) or becomes turbulent, clots start to form.

For example:

  • Stasis:
    • Due to immobilisation / prolonged bedrest
    • Left atrial dilatation due to mitral stenosis
  • Turbulent flow:
    • Arterial stenosis (narrowing of the vessels)
    • Cardiac wall dysfunction
    • Atrial fibrillation
  1. Endothelial damage:

Damage to the vessel walls expose the subendothelial collagen fibres and trigger platelet adhesion, aggregation and the clotting cascade to occur (listen to our haemostasis podcast).

Diseases that precipitate thrombi formation from vessel damage include:

  • Atherosclerosis
  • Vasculitis
  • High levels of homocysteine (from B12 and Folate deficiency)
    • can lead to atherosclerosis
  • Cigarette smoking
  1. Where the blood is in a hypercoagulable state

A disease causes a hypercoagulable state in the blood by having either too much pro-coagulation factors or too little anti-coagulant proteins. Patients with these diseases will present with recurrent DVTs or at a very young age.

Disease include:

  • Activation of coagulation system
    • Disseminated Intravascular Coagulation (DIC)
  • Hereditary or acquired factor deficiencies
    • Hereditary antithrobin III deficiency
    • Oral Contraceptives (Estrogen)
  • Antiphospholipid syndrome
    • Due to lupus anticoagulant
  • Thrombocytosis: (Too many platelets)
    • Malignancy

References:

  • Pathoma 2011
  • Goljan Rapid Review of pathology 4th ed.

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