Paper I
Question
List the components of Virchow’s triad. Describe how each of the components leads to thrombosis with suitable examples
Answer
Components of Virchow’s triad
- Endothelial (vascular) injury
- Abnormal blood flow (stasis or turbulence)
- Hypercoagulability of blood
1. Endothelial injury
- Damaged endothelium exposes subendothelial collagen and releases tissue factor, triggers platelet adhesion/activation, and loses its normal antithrombotic properties (loss of prostacyclin, NO, thrombomodulin)
- Examples: myocardial infarction (endocardial injury over infarct), vasculitis, atherosclerotic plaque ulceration, hypertension
2. Abnormal blood flow
- Stasis: Allows platelets and clotting factors to accumulate near the vessel wall (not washed away), promotes endothelial cell activation, and prevents dilution of activated clotting factors
- Examples: atrial fibrillation (blood stasis in the left atrium/appendage), immobilization/prolonged bed rest (deep vein thrombosis), aneurysms
- Turbulence: Causes endothelial injury/dysfunction and forms countercurrents/local stasis
- Examples: at arterial bifurcations, over atherosclerotic plaques
3. Hypercoagulability
- Primary (genetic): Factor V Leiden mutation, prothrombin gene mutation, protein C/S deficiency, antithrombin III deficiency
- Secondary (acquired): Malignancy (tumour procoagulant release — Trousseau syndrome), pregnancy/oral contraceptive use (oestrogen-related), nephrotic syndrome (loss of antithrombin III in urine), prolonged immobilization, antiphospholipid antibody syndrome, smoking