## Virchow's Triad: The Three Pillars of Thrombosis **Key Point:** Virchow's triad consists of three major pathophysiologic factors that predispose to thrombosis: (1) endothelial injury, (2) stasis or turbulent blood flow, and (3) alterations in blood composition (hypercoagulability). ### The Three Components | Component | Mechanism | Clinical Examples | |-----------|-----------|-------------------| | **Endothelial Injury** | Damage to vessel wall exposes TF and vWF | Atherosclerotic plaque rupture, trauma, indwelling catheters | | **Stasis/Turbulence** | Reduced or chaotic flow allows platelet–fibrin deposition | Atrial fibrillation, venous obstruction, aneurysms | | **Hypercoagulability** | Imbalance favoring coagulation over anticoagulation | Malignancy, pregnancy, oral contraceptives, thrombophilia | **High-Yield:** All three factors need not be present simultaneously; even one can initiate thrombosis, but the presence of multiple factors dramatically increases risk. ### Why Increased Blood Viscosity Is NOT Part of Virchow's Triad **Warning:** Increased blood viscosity (as in polycythemia or severe dehydration) is a *separate* risk factor for thrombosis, but it is NOT formally part of Virchow's triad. Virchow's triad specifically addresses flow dynamics (stasis/turbulence), not blood viscosity per se. **Clinical Pearl:** Viscosity affects flow and can contribute to stasis, but the classic triad focuses on the three mechanistic pillars identified by Virchow in the 19th century. 
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