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Virchow's Triad and Thrombus Formation

Jul 15, 2024

Lecture Notes: Virchow's Triad and Thrombus Formation

Thrombus vs. Embolus

  • Thrombus: A blood clot.
  • Embolus: Any detached intravascular solid, liquid, or gaseous mass carried by the blood to a distant site from its origin.
    • A thrombus can become an embolus (or thromboembolus) if a piece of the blood clot breaks off and lodges in a different part of the vasculature.

Virchow's Triad

Virchow's Triad describes three primary abnormalities that lead to thrombus formation:

  1. Endothelial Injury: Injury to the blood vessel’s inner wall.
    • Causes: Hypertension, infection, toxins, metabolic disturbances like hyperlipidemia.
    • Results in exposure of the subendothelial extracellular matrix, initiating a clotting cascade (platelet adhesion, tissue factor release, fibrin clot formation).
  2. Turbulence/Stasis of Blood Flow: Abnormal flow and stagnant blood.
    • Turbulence: Disorganized flow leading to endothelial injury.
    • Stasis: Slow or stationary blood increases platelet contact with the vessel wall.
  3. Hypercoagulability: An increased tendency to clot.
    • Primary Causes: Genetic mutations in clotting factors (e.g., Factor V Leiden).
    • Secondary Causes: Acquired conditions like atrial fibrillation.

Fate of a Thrombus

  1. Dissolution: Thrombus dissolves via fibrinolysis.
  2. Propagation: Thrombus grows by accumulating more platelets and fibrin.
  3. Recanalization: Formation of capillary channels within the thrombus to restore blood flow.
  4. Embolization: Part of the thrombus breaks off and travels to another site in the vasculature.

Clinical Consequences

  • Venous Thrombi: Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE).
    • DVT: Thrombus in the deep veins of the legs.
    • PE: A piece of DVT breaks off, travels, and lodges in the pulmonary vasculature causing respiratory distress and potentially death.
  • Arterial Thrombi: Occlusion of crucial arteries.
    • Coronary arteries: Myocardial infarction (heart attack).
    • Cerebral arteries: Stroke.
  • Disseminated Intravascular Coagulation (DIC): Widespread fibrin thrombi in microcirculation causing circulatory insufficiency and concurrent widespread bleeding.

Types of Emboli

  • Thromboembolus: Thrombus that becomes an embolus.
  • Fat Embolus: Fat droplets from bone marrow entering circulation (usually after major trauma).
  • Amniotic Fluid Embolus: Amniotic fluid enters maternal vasculature (after trauma to the womb).
  • Location Importance:
    • Arterial Source: Embolus can travel to abdominal organs, brain, or extremities.
    • Venous Source: Embolus typically ends up in pulmonary vasculature.
    • Rare Case: Venous embolus passes through heart defect into arterial vasculature, causing a stroke.

Summary

Understanding the difference between a thrombus and an embolus, the factors contributing to thrombus formation (Virchow's Triad), and the possible outcomes and clinical implications of thrombi is crucial for managing and preventing complications associated with blood clots.

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