Stasis, endothelial injury and hypercoagulability
Mnemonic
Three contributors to thrombosis:
- Stasis - immobility, long flights, atrial fibrillation, varicose veins, plaster casts
- Endothelial injury - surgery, trauma, cannulation, atherosclerosis, smoking, inflammation
- Hypercoagulability - malignancy, pregnancy and the puerperium, oestrogens, thrombophilia, nephrotic syndrome, sepsis, dehydration
“Slow flow, damaged wall, sticky blood.”
Almost every risk factor on a thromboprophylaxis assessment falls into one of the three, which is why the triad is worth carrying: surgery ticks all three at once, which is why postoperative venous thromboembolism is so common.
Arterial thrombosis is dominated by endothelial injury, forming platelet rich white thrombus, which is why it is treated with antiplatelets. Venous thrombosis is dominated by stasis and hypercoagulability, forming fibrin rich red thrombus, which is why it is treated with anticoagulants.
Expansion
- Stasis or turbulent flow: immobility, long flights, heart failure, atrial fibrillation, varicose veins, pregnancy, obesity
- Endothelial injury: surgery, trauma, central lines, atherosclerosis, vasculitis, smoking, hypertension, indwelling catheters
- Hypercoagulability: malignancy, pregnancy and the puerperium, oestrogens, inherited thrombophilias, nephrotic syndrome, sepsis, dehydration, antiphospholipid syndrome
Arterial thrombi form under high flow, are platelet rich, appear pale, and are usually driven by endothelial injury from atherosclerosis. Venous thrombi form under low flow, are red and fibrin rich, and are usually driven by stasis.
This difference explains why antiplatelet drugs are used for arterial disease while anticoagulants are used for venous disease.
Lines of Zahn (alternating pale platelet and dark red cell layers) indicate a thrombus formed in flowing blood during life, distinguishing antemortem thrombus from post-mortem clot at autopsy.
Fate of a thrombus: propagation, embolisation, dissolution by fibrinolysis, organisation with recanalisation, or organisation with permanent occlusion.