41.2 Thrombosis

Question 1

What is thrombosis?

Answer 1

“Haemostasis in the wrong place”

Question 2

What is a thrombus?

Answer 2

A blood clot that forms in situ within a blood vessel that impedes blood flow.

Question 3

Compare how arterial and venous thrombi form.

Answer 3

Arterial thrombosis occurs as a result of platelet activation through endothelial damage and abnormal blood flow (atherosclerosis)
Venous thrombosis occurs as a result of stasis and hypercoagulability resulting in blood clot formation NOT platelet activation

Question 4

What is Virchow’s triad?

Answer 4

3 main factors that promote thrombosis:
* Changes in the intimal surface of the vessel
* Changes in the pattern of blood flow
* Changes in blood constituents
These apply to arterial and venous thrombosis, and atrial fibrillation.

Question 5

Give examples of changes in the intimal surface of the vessel

Answer 5

• Atherosclerosis
• Trauma
• Inflammation
• Neoplasia

Question 6

Give examples of changes in the pattern of blood flow

Answer 6

• Changes in speed -> Systemic (e.g. heart failure) or local (e.g. immobilisation)
• Turbulent blood flow -> Atrial aneurysm, atrial fibrillation, myocardial infarction

Question 7

Give examples of changes in blood constituents

Answer 7

• Increased procoagulant factors
• Decreased anticoagulant factors
• Increased blood viscosity
• Increased platelet numbers and adhesion/aggregation
• Presence of anticardiolipin antibodies (eg in SLE)
• Release of procoagulant factors by tumours

Question 8

How does endothelial injury contribute to thrombus formation?

Answer 8

Endothelial injury which leads to platelet activation
-exposes vWF and tissue factor
-cytokines downregulate thrombomodulin expression
-activated endothelial cells secrete Plasminogen activator inhibitors (limit fibrinolysis)

Question 9

What is deep vein thrombosis (DVT)?

Answer 9

The formation of a thrombus in a deep vein, most commonly in the legs or pelvis.
*These thrombi are serious because they are prone to embolise

Question 10

Where do DVT thrombi end up?

Answer 10

Travel as an embolus to the right side of the heart and block the pulmonary artery which supplies blood to the lungs (pulmonary embolism)

Question 11

Give examples of vessels in which DVT occurs?

Answer 11

Larger leg veins at or above the knee joint
Popliteal
Femoral
Iliac

Question 12

What are some risk factors for venous thrombosis?

Answer 12

• Age
• Venous stasis (esp. in the elderly) - immobilisation and bed rest
• Any surgery (esp. orthopaedic and prostate)
• Pregnancy
• Infection
• Malignancy (esp. adenocarcinomas)
• Genetic
  
  • AT-III deficiency
  • Protein C Resistance (incl. Factor V Leiden)

Question 13

What are the effects of ARTERIAL thrombosis?

Answer 13

Stenosis
Ischaemia
Infarction
Embolism

(higher tendency to block vessels whereas venous do not totally occlude)

Question 14

What are the effects of VENOUS thrombosis?

Answer 14

Embolism
Oedema
Venous leg ulcers
Local congestion and swelling from impaired outflow
Obstruction/Ischaemia (depends on site)

Question 15

What is stenosis?

Answer 15

the abnormal narrowing of a blood vessel or other tubular organ or structure such as foramina and canals.

Question 16

How does hypercoagulability contribute to the development of thrombi? Give an example

Answer 16

Defined as an abnormaly high ability of the blood to clot through alterations in coagulation factors
Mutations in factor V (Leiden) which renders it resistant to proteolysis by active protein C (anti-thrombotic counterregulatory mechanism is lost)

Question 17

How does thrombin regulate the clotting cascade?

Answer 17

Thrombin cleaves fibrinogen to fibrin (pro-coagulation)
Cleaves Factor V to Va which cleaves prothrombin to thrombin
Thrombin binds to thrombodulin (activates protein C which has anti-coagulant activity)

Question 18

What are venous leg ulcers?

Answer 18

Long-lasting sores in the skin that take more than a month to heal.