PA5.3-5 | Thrombosis, Embolism, Infarction & Shock — Summary & Reflection

REFLECT

A 35-year-old woman with antiphospholipid syndrome is admitted with a proximal DVT and started on heparin. Two days later, her platelet count drops from 220 to 55 × 10⁹/L, and she develops a new arterial thrombosis in her arm.

Think through: (1) Which element of Virchow's triad did her antiphospholipid syndrome originally activate, and by what mechanism? (2) What is heparin-induced thrombocytopaenia (HIT) and which Virchow element does the resulting immune complex activate? (3) Why is she paradoxically thrombosing more despite being anticoagulated?

Discuss with a colleague or write three bullet points before scrolling to the summary.

KEY TAKEAWAYS

Core framework — Hemodynamic Disorders (Part 2):

Thrombosis is driven by Virchow's triad: endothelial injury (dominant in arteries), stasis/turbulence (dominant in veins), and hypercoagulability. Arterial thrombi are pale/platelet-rich; venous thrombi are red/fibrin-rich. Lines of Zahn confirm ante-mortem arterial formation. Thrombi may propagate, embolize, dissolve, or organise.

Embolism: Thromboembolism (DVT → PE) is the commonest type. Fat embolism (long-bone fracture) = hypoxia + petechiae + confusion at 24-72 hr. Amniotic fluid embolism is rare but catastrophic. Saddle embolus → sudden death.

Infarction: Red = haemorrhagic = loose tissue / dual supply / venous occlusion (lung, bowel). White = anaemic = solid organ with end-arterial supply (kidney, spleen). Nature of vascular supply is the single most important determinant.

Shock: Systemic hypoperfusion → cellular hypoxia. Three stages: compensated → progressive (lactic acidosis, DIC) → irreversible (cell death, organ failure). Septic shock: LPS → cytokine storm → DIC → multi-organ failure. Target organs: kidney (ATN), lung (ARDS), adrenal (Waterhouse-Friderichsen), brain (ischaemic encephalopathy).

Always connect mechanism → morphology → clinical presentation — this is the clinico-pathological correlation that will define your examination answers and your bedside reasoning.