Pathophysiology of Thrombosis and Embolism

Question 1

What is normal flow of blood?

Answer 1

Laminar

Question 2

What is meant by stasis?

Answer 2

Stagnation of flow

Question 3

What is meant by turbulence?

Answer 3

Forceful unpredictable flow

Question 4

What are the causes of common defects in blood flow?

Answer 4

Thromboembolism

Atheroma

Hyperviscosity

Spasm

External compression

Vasculitis vascular steal

Question 5

What is meant by Virchow’s triad?

Answer 5

• Changes in the blood vessel wall
• Changes in the blood constituents
• Changes in the pattern of blood flow

Question 6

What does Virchow’s triad influence?

Answer 6

They are the factors causing thrombosis

Question 7

Give an example of a change in the vessel wall

Answer 7

Atheromatous coronary artery

Question 8

What is the basic pathogenesis of thrombosis?

Answer 8

Endothelial injury

Stasis or turbulent blood flow

Hypercoagulability of the blood

Question 9

What are lines of Zahn on a thrombus?

Answer 9

Represent bands of fibrin (lighter) with entrapped white blood cells and red blood cells (darker).

Question 10

What causes the adherence of platelets?

Answer 10

Loss of intimal cells and the exposure of collagen

Question 11

What traps red blood cells in a blood clot?

Answer 11

Fibrin meshwork

Question 12

What is responsible for the propagation of thrombosis?

Answer 12

Further turbulence and platelet deposition

Question 13

What is the relationship between atheroma and thrombosis?

Answer 13

Arterial thrombosis most commonly superimposed on atheroma; Virchow’s triad

Question 14

What are the possible changes in the blood constituents (Virchow’s triad) that can result in thrombosis?

Answer 14

Hyperviscosity, post-operative traumatic hypercoagulability

Hypercholesterolaemia

Question 15

What are the possible alterations in blood flow (Virchow’s triad) that can result in thrombosis?

Answer 15

Stasis - post op “economy class syndrome”

Turbulence: atheromatous plaque, aortic aneurysm

Question 16

What do the consequences of thrombosis depend on?

Answer 16

Site, extent and colalteral circulation

Question 17

What are the resolutions of thrombosis?

Answer 17

Resolution

Organisation/recanalisation

Death

Propagation - embolism

Question 18

What is embolism defined as?

Answer 18

Movement of abnormal material in the bloodstream and its impact in a vessel, blocking its lumen

Question 19

What is an embolus?

Answer 19

Detatched intravascular solid, liquid or gaseous mass

Question 20

What is a thromboembolism?

Answer 20

Embolus resulting from dislodged thrombus

Question 21

What is a systemic/arterial thromboembolus?

Answer 21

Mural thrombus

Aortic aneurysms

atheromatous plaques

Valvar vegetations

Venous thrombi - paradoxical emboli

Question 22

What are mural thrombi associated with?

Answer 22

Myocardial infarction or left atrial dilation and atrial fibrilation

Question 23

Where can a systemic thrombus travel to?

Answer 23

Wide variety of sites: lower limbs most common, brain and other organs.

Question 24

What is the usual result of a systemic thromboembolus?

Answer 24

Infarction.

Consequences depend on:

• vulnerability of affected tissues to ischaemia
• amount of occluded vessel
• collateral circulation

Question 25

What is a venous thromboembolus?

Answer 25

Originate from deep venous thromboses (lower limbs)

Most common form of thromboembolic disease

Question 26

Where do venous thromboembolus usually travel amd occlude?

Answer 26

Travel to the pulmonary arterial circulation, may occlude the main pulmonary artery, bifurcation or smaller arteries

Question 27

What are the possible consequences of thromboembolism?

Answer 27

Depend on size of embolus: silent, pulmonary haemorrhage/infarction, right heart failure, sudden death

Multiple PE over time: pulmonary hypertension and right ventricular failure

Question 28

What are risk factors for deep vein thrombosis and pulmonary embolism?

Answer 28

• Cardiac failure
• Severe trauma
• Burns
• Post op
• Post partum (following childbirth)
• Nephrotic syndrome
• disseminated malignancy
• Oral contraceptive
• Increased age
• Obesity
• Bed rest/immobilisation
• Past medical history of deep vein thrombosis

Question 29

What is prophylaxis for deep vein thrombosis?

Answer 29

TEDS - long, tight fitting stockings that place mild static pressure on legs to prevent blood clotting

Heparin - compound occurring in liver and other tissues which inhibits blood coagulation

Question 30

When might you suffer from a fat embolism?

Answer 30

After fracture

Syndrome of fat embolism: brain, kidneys, skin affected

Question 31

What is gas embolus?

Answer 31

N2 forms as bubbles which lodge in capillaries

Decompression sickness

Question 32

Apart from diving when can you get an air embolism?

Answer 32

Surgery - Small amounts of air gets into blood circulation accidentally during surgery and other medical procedures (for example a bubble entering an intravenous fluid line)

Most air emboli enter veins and are stopped at lungs, venous air embolism showing any symptoms is very rare

Question 33

Apart from systemic thrombus, DVT, Fat and gas what are the other types of embolus?

Answer 33

Tumour

Trophoblast - layer of tissue on outside of mammalian blastula, supplying embryo with nourishment and later forming major part of placenta

Septic material (e.g infective endocarditis)

Amniotic fluid (cause of collapse)

Bone marrow (fractures)

Foreign bodies (Intravascular cannulae tips, sutures)