Thrombosis and Embolism

Question 1

Thrombosis

Answer 1

The process leading to thrombus formation

Question 2

Thrombus’ main constituents

Answer 2

Platelets and fibrin

Question 3

When can thrombosis be physiological

Answer 3

To prevent bleeding when a vessel wall is breached

Question 4

What process limits physiological thrombosis and how relate to pathological thrombosis

Answer 4

Fibrinolysis

Thrombosis becomes pathological when it is not controlled by fibrinolysis

Question 5

What holds a thrombus together

Answer 5

Fibrin

Question 6

Describe the process of physiological thrombosis

Answer 6

Vessel wall is breached and so circulating platelets aggregate to plug the gap

Platelets release factors which trigger coagulation cascade which converts fibrinogen into insoluble fibrin that wraps together platelets and entrapped RBCs and WBCs

Question 7

Plasmin

Answer 7

Active enzyme that fragments/degrades fibrin and thus blood clots

Question 8

Fibrin degradation products (FDPs)

Answer 8

Fragmented bits of fibrin after degradation

Question 9

Describe the process of normal finrinolysis

Answer 9

Inactive plasminogen in plasma becomes plasmin via plasminogen activators (specifically tissue plasminogen activator t-PA)

When fibrin is formed, plasminogen and t-PA bind to it; t-PA activates nearby plasminogen, leading to fibrin degradation

This controls thrombus size

Question 10

How might pathological thrombosis occur (simple)

Answer 10

Thrombus grows beyond vessel healing requirements and continues to grow to a size and rate beyond which the fibrolytic system is incapable of controlling the size

Question 11

D-Dimers and D-Dimer test

Answer 11

D-Dimers are a breakdown product of fibrin mesh, stabilised by factor XIII;

Increased levels may indicate thrombotic events

Question 12

Factors that predispose thrombus formation (Virchow’s Triad)

Answer 12

Damage to vessel wall (especially endothelium)

Stasis of blood

Change in blood character (especially increases in platelets, RBCs and viscosity)

Question 13

How is arterial thrombosis most likely to occur

Answer 13

Main predisposing factor is vessel wall damage

Question 14

How is venous thrombosis most likely to occur

Answer 14

Stasis is the most important factor

Question 15

How is thrombosis of the heart most likely to occur in the ventricles

Answer 15

Chamber wall damage is the most important factor here

Question 16

How is thrombosis of the heart most likely to occur in the atria

Answer 16

Stasis of blood is the most important factor

Question 17

How is thrombosis of the heart valves most likely to occur

Answer 17

Valve surface damage is the most important factor

Question 18

What may happen to a thrombus in pathological thrombosis

Answer 18

It may be lysed via fibrinolysis (rare)

Occlude the lumen

Extending locally

May undergo organisation & recanalisation

Fragment and detach completely, traveling elsewhere and becoming a thrombo-embolism

Question 19

What does thrombotic occlusion cause in an artery

Answer 19

This cuts off blood flow and can cause an infarction

Question 20

What does thrombotic occlusion cause in a vein

Answer 20

It prevents venous drainage of tissues, blood pools that cannot escape –> congestion and often haemorrhagic infarctions

Question 21

Recanalisation

Answer 21

Re-establishment of blood flow into a formerly occluded region

Question 22

Organisation & Recanalisation of Thrombus

Answer 22

New vessels grow into the thrombus, vascular granulation tissue develops

Fibroblasts invade and deposit collagen and so fibrovascular granulation tissue develops

This is an organised thrombus; when vessels link up, some degree of recanalisation may occur

Question 23

Granulation tissue

Answer 23

New connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process

Question 24

Embolism

Answer 24

Transference of abnormal material by blood stream with eventual impaction of material in a vessel distal to origin

Question 25

Most notable embolised materials

Answer 25

Thrombuses and cancer cells (metastasis)

Question 26

Thromboembolism

Answer 26

A thrombus breaks off and passes into blood stream to a distal site where they impact and occlude a distal vessel

Question 27

What would a thromboembolism of lower limb arteries cause

Answer 27

Gangrene of legs

think ischaemia

Question 28

What might a thrombus in a systemic vein cause

Answer 28

This is likely to embolise to a pulmonary artery branch and cause a pulmonary embolus (economy class syndrome)

Question 29

Venous Thromboembolism Risk Assessments

Answer 29

Be vaguely aware

Question 30

Some important risk factors of VTE

Answer 30

Active cancer/cancer treatment
Age ?60
Dehydration
Obesity
Significant medical comorbidities (e.g. heart disease)
Personal/Close family history
HRT
Contraceptives
Pregnancy/Post partum

Question 31

Other materials that can cause embolism

Answer 31

Fat/Marrow
Air
Nitrogen (Decompression sickness)
Amniotic Fluid