Venous Thromboembolism (VTE) - Pathophysiology

Question 1

What is Haemostasis?

Answer 1

A physiological process resulting in the rapid formation of a solid plug at the site of injury to stop haemorrhage when there is damage to a blood vessel.

Question 2

What is the plug made up of in Haemostasis?

Answer 2

1. Platelets.
2. Fibrin.
3. Red Blood Cells.

Question 3

What is the purpose of Fibrinolysis?

Answer 3

Ensure the haemostatic process is controlled.

Question 4

What happens in Haemostasis (3)?

Answer 4

1. Endothelial injury leads to platelet adhesion and aggregation (using Thromboxane A2 and ADP).
2. Platelets adhere to collagen by vWF and red blood cells become enmeshed with the platelets - primary loose platelet plug.
3. Exposure of tissue factor initiates coagulation cascade to form insoluble fibrin. Fibrin stabilises the primary plug to form a stable secondary platelet plug.

Question 5

What happens in Fibrinolysis?

Answer 5

1. Injury releases TPA and UPA (Tissue and Urokinase-Like Plasminogen Activators).
2. TPA and UPA activate Plasminogen into Plasmin.
3. Plasmin solubilises fibrin into soluble products.

Question 6

What is Thrombosis?

Answer 6

Inappropriate activation of haemostats, overwhelming the capacity of the fibrinolytic system, resulting in the formation of a solid plug - thrombus.

Question 7

What is a thrombus made up of?

Answer 7

Same components as a haemostatic plug.

Question 8

Give 3 differences between a thrombus and a clot.

Answer 8

1. Thrombus - RBC + Fibrin + Platelets. Clot – RBC + Fibrin.
2. Thrombus - Within Cardiovascular System. Clot - Outside Cardiovascular System.
3. Thrombus - Flowing Blood. Clot - Stationary Blood.

Question 9

What is Virchow’s Triad?

Answer 9

3 Major Predisposing Factors to Thrombus Formation :

1. Endothelial Injury.
2. Abnormal Blood Flow.
3. Hypercoagulability.

Question 10

Give 3 causes of endothelial injury.

Answer 10

1. Atherosclerosis.
2. Vasculitis.
3. Direct Trauma.

Question 11

Give 2 types of abnormal blood flow.

Answer 11

1. Turbulence (atherosclerosis, artificial valves, stents).

2. Stasis (post-operative, heart failure, immobility, mass, aneurysms)

Question 12

Give 2 causes of hypercoagulability (2).

Answer 12

1. Too many blood cells (erythrocytosis, thrombocytosis).

2. Coagulation Factor Defects.

Question 13

Give 3 Hereditary Coagulation Factor Defects.

Answer 13

1. Factor V Leiden.
2. Protein C Deficiency.
3. Protein S Deficiency.

Question 14

Give 6 Acquired Coagulation Factor Defects.

Answer 14

1. OCP.
2. Malignancy.
3. Pregnancy.
4. Lupus.
5. Anticoagulant.
6. DIC.

Question 15

What are the most important risk factors for arterial vs venous thrombosis?

Answer 15

Arterial - Atherosclerosis.

Venous - Stasis and Hypercoagulability.

Question 16

What is Ischaemia?

Answer 16

(Reversible) Tissue dysfunction due to interference with blood flow to a tissue.

Question 17

What is Infarction?

Answer 17

(Irreversible) Tissue death due to interference with blood flow to a tissue.

Question 18

What is Necrosis?

Answer 18

Cell death due to a pathological process.

Question 19

What is Embolism?

Answer 19

Occlusion of a vessel by undissolved material that is transported in the blood stream.

Question 20

Types of Emboli.

Answer 20

1. Fat - Bone Trauma.
2. Air.
3. Thrombus.
4. Amniotic Fluid.
5. Septic - Infected Material e.g. Infective Endocarditis.

Question 21

What does an Amniotic Fluid Embolus contain?

Answer 21

It contains cells from the foetal skin (squames) which can enter the maternal circulation to cause ARDS and DIC.