6. Thrombus and embolism

Define thrombosis

Pathological formation of a blood clot (thrombus) inside the vascular system/heart in a living person

Thrombus vs clot

Thrombus: intravascular, always pathological, attached to the wall

Clot: forms in an injured vessel to stop bleeding (haemostasis)

A thrombus is made of…

Platelets + fibrin (± trapped RBCs and leukocytes)

⚠ Your notes said: platelets + fibrinogen — the mesh is FIBRIN.

Virchow's triad: _____, _____, _____

endothelial injury | abnormal blood flow (stasis/turbulence) | hypercoagulability

Virchow: causes of endothelial injury

Atherosclerosis, trauma, toxins (smoking), hypertension, ischaemia, inflammation

Virchow: causes of stasis

Immobilisation, varicose veins, heart failure, AF, aneurysm

Virchow: causes of hypercoagulability

Dehydration (↑ viscosity), polycythaemia/thrombocytosis, malignancy, pregnancy, oral contraceptives, inherited (factor V Leiden)

Thrombus formation: platelets _____ to damaged endothelium → _____ → slowed flow traps _____ → coagulation produces _____

adhere | aggregate | RBCs | fibrin

Arterial thrombosis: sites, cause, result

Coronary, cerebral, femoral/iliac arteries

On atherosclerotic plaques (fast flow)

→ ischaemic infarcts (MI, stroke)

Venous thrombosis: sites, cause, result

Deep leg veins, superficial varicose veins

Stasis (immobility, surgery, childbirth)

→ pulmonary embolism

Cardiac thrombosis — dangers

Large thrombus in the heart → mechanical obstruction (sudden death) or systemic thromboembolism

Capillary thrombosis can lead to…

DIC — widespread microthrombi consume clotting factors → bleeding

Possible fates of a thrombus

• Fibrinolysis (dissolution)

• Organisation + recanalisation

• Propagation

• Embolisation

Define embolism

Passage through vessels of any material that lodges and obstructs the lumen

Define embolus

An intravascular mass transported from its site of origin

3 features of an embolus: it _____, is _____, and _____

travels a distance | foreign to normal blood | obstructs flow

Orthograde venous embolism — route

Systemic veins → right heart → pulmonary arteries (pulmonary embolism)

Notes: 'from the big circle to the small circle'.

Orthograde arterial embolism — route

Left heart/aorta → systemic arteries (brain, kidney, spleen, limbs)

Retrograde embolism — what and example

Embolus moves against blood flow (gravity/↑ intrathoracic pressure)

E.g. prostate carcinoma cells to vertebrae via the vertebral venous plexus

Paradoxical embolism

A venous embolus crosses to the arterial side through a patent foramen ovale (or ASD/VSD) → systemic arterial occlusion (e.g. stroke)

⚠ Your notes said: 'through a CLOSED foramen ovale' — it must be PATENT.

Exogenous emboli

Air, gas (decompression in divers), bacteria (septic), foreign bodies

Endogenous emboli

Thrombus (most common), fat (long-bone fracture, liposuction), atheromatous plaque, tumour cells, amniotic fluid

Most common type of embolus

Thromboembolus

How many Virchow factors are usually needed for thrombosis?

Usually 2 of the 3 together raise the risk significantly (e.g. immobility + hypercoagulability after surgery)

Why are many DVTs asymptomatic?

The vein is not fully occluded and/or collateral veins drain the limb

Classic signs of DVT

Calf pain, swelling, warmth, deep muscle tenderness (one leg)

Air embolism — mechanism

Laceration of a large neck vein (e.g. jugular) or IV line: venous pressure below atmospheric sucks air in → foamy air in the right ventricle blocks outflow ('air lock')

~100 mL can be fatal

Gas (decompression) embolism — mechanism

Rapid ascent (divers): dissolved nitrogen comes out of solution as bubbles when ambient pressure falls (Henry's law) → 'the bends', bubbles in vessels

Fat embolism — mechanism

Long-bone fracture releases yellow-marrow fat into torn veins → lungs → fat embolism syndrome: dyspnoea, petechiae, confusion (24–72 h)

EXAMINER ASKS: What happens clinically after a large pulmonary embolus?

Acute right heart strain (↑ pulmonary vascular resistance), V/Q mismatch → hypoxaemia, dyspnoea, chest pain, tachycardia

A saddle embolus can cause sudden death

EXAMINER ASKS: Why do venous thrombi form in the legs but arterial thrombi on plaques?

Veins: slow flow / stasis dominates (red thrombus, many RBCs).

Arteries: fast flow washes RBCs away — thrombi need endothelial injury (plaque rupture) and are platelet-rich (white thrombus).

15-MINUTE NOTES / Write your note sheet for essay 06 Thrombosis and embolism

1. Thrombosis: def, thrombus vs clot, composition

2. Virchow's triad with examples (2 of 3 needed)

3. Pathogenesis steps

4. Types: arterial, venous, cardiac, capillary (DIC)

5. Fates of thrombus

6. Embolism: def, 3 features

7. Types by route: orthograde, retrograde, paradoxical

8. By material: thrombo-, fat, air, gas, amniotic, tumour, septic

Draw: Virchow's triad as a triangle, and the route of a DVT embolus: leg vein → IVC → right heart → pulmonary artery