Pathophysiology of Thrombosis and Embolism

Question 1

What defects in blood flow can result in thrombosis and embolism?

Answer 1

Atheroma
Hyperviscosity
Spasm
External compression
Vasculitis 
Vascular steal syndrome

Question 2

What is normal blood flow?

Answer 2

Laminar - smooth and ordered

Question 3

What is the vascular system affected by?

Answer 3

Pressure gradient
Resistance
Blood viscosity
Compliance of the vessel

Question 4

What features of blood flow are abnormal?

Answer 4

Stasis

Turbulence

Question 5

What is stasis of blood flow?

Answer 5

Stagnation of blood flow e.g. in cardiac failure where there is not enough force to push the blood

Question 6

What is turbulence of blood flow?

Answer 6

Forceful, unpredictable flow e.g. due to something protruding into the lumen such as an atheromatous plaque
Noisy on auscultation

Question 7

What are the components of Virchow’s triad?

Answer 7

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

Question 8

What is the most important risk factor for thrombus formation?

Answer 8

Hypercholesterolaemia

Question 9

What is thrombosis?

Answer 9

Formation of a solid mass from the constituents of blood within the vascular system during life

Question 10

What steps are involved in the pathogenesis of thrombosis?

Answer 10

Endothelial injury
Stasis or turbulent flow
Hypercoagulability of the blood

Question 11

What effect does an atheromatous plaque have on blood flow when it starts to protrude from the lumen?

Answer 11

Starts to cause turbulent flow

Question 12

What does turbulent blood flow cause?

Answer 12

Damage to the endothelial surface - loss of intimal cells and denuded plaque

Question 13

What happens when the endothelial surface is lost due to turbulent flow?

Answer 13

Collagen in the fatty core of the plaque is exposed to the blood, platelets in the blood then stick to the collagen and form a fibrin meshwork which traps the RBCs

Question 14

What do alternating bands of fibrin and RBCs form?

Answer 14

Lines of Zahn

Question 15

What do the consequences of thrombosis depend on?

Answer 15

Site
Extent
Collateral circulation

Question 16

What are common consequences of thrombosis?

Answer 16

DVT
Ischaemic limb
MI

Question 17

What are possible outcomes of thrombosis?

Answer 17

Resolution
Organisation/recanalisation
May relieve itself but often medical intervention is needed to break down the platelets and restore blood flow

Question 18

What will organisation/recanalisation cause?

Answer 18

Restoration of blood flow, but tissue damage may still occur as thrombus is stabilised, endothelial surface grows and fibrosis and granulation can occur along with the formation of new blood vessels

Question 19

What is embolism?

Answer 19

Movement of abnormal material in the blood stream and its impaction in a vessel, blocking its lumen

Question 20

What substances can form an embolus?

Answer 20

Detached intravascular solid, liquid or gaseous mass

Question 21

What are most emboli formed from?

Answer 21

Detached thrombi

Question 22

What are some causes of thromboembolism?

Answer 22

Systemic/arterial thromboembolism 
Mural thrombus 
Aortic aneurysm
Atheromatous plaque
Valvular vegetations

Question 23

What are the features of a systemic thromboembolism?

Answer 23

Travels to a wide variety of sites - lower limbs most common but brain and other organs also affected
Usually infarction occurs

Question 24

What do the consequences of a systemic thromboembolism depend on?

Answer 24

Vulnerability of the affected tissues to ischaemia
Calibre of occluded vessel
Collateral circulation

Question 25

Where do most venous thromboembolisms originate from?

Answer 25

Deep venous thromboses in the lower limbs

Question 26

What is the most common form of thromboembolic disease?

Answer 26

Venous thromboembolism

Question 27

Where do venous thromboembolisms travel to? What can this cause?

Answer 27

Pulmonary arterial circulation | May occlude the main pulmonary artery, bifurcation or small arteries

Question 28

What do the consequences of a venous thromboembolism depend on?

Answer 28

Size of the embolus

Question 29

What are the potential consequences of venous thromboembolism?

Answer 29

``` May be silent Pulmonary haemorrhage Pulmonary infarction Right heart failure Sudden death ```

Question 30

What do multiple pulmonary emboli cause over time?

Answer 30

Pulmonary hypertension and right ventricular failure

Question 31

What are the possible types of embolus?

Answer 31

``` Fat Gas Air Tumour Trophoblast Septic material Amniotic fluid Bone marrow Foreign bodies ```

Question 32

What are the risk factors for DVT and pulmonary thromboembolism?

Answer 32

``` Cardiac failure Severe trauma/burns Post-operative or post-partum state Nephrotic syndrome Disseminated malignancy OCP Increasing age Bed rest/immobilisation Obesity PMH of DVT ```

Question 33

What does prophylaxis for surgical patients at risk of DVT and pulmonary embolism include?

Answer 33

TEDS and subcutaneous heparin