W2 7 Thromboembolic Disease

Question 1

What is a thrombus?

Answer 1

A solid mass present within the vascular system during life formed by the constituents of blood

Question 2

Differences between a thrombus and a post-mortem clot in terms of consistency, colour and adherence to vessel wall
(Useful to know if it was there before death or contributed to death)

Answer 2

Thrombus: firm/brittle consistency; variable colour: might be pale or red, or laminated with alternating bands of each (lines of Zahn); adherent to vessel wall
Post-mortem clot: gelatinous consistency; pale on top and dark red underneath; not adherent to vessel wall

Question 3

When do pale thrombi form?

Answer 3

Tend to form in high flow environments (arteries/heart) due to turbulence or endothelial injury

Question 4

What are pale thrombi composed of? (Image pg58)

Answer 4

Mainly composed of platelets

Question 5

What types of pale thrombi are there?

Answer 5

Mural (stuck on the wall) or occlusive (depends on size of vessel)

Question 6

What are the 3 causes of arterial thrombosis?

Answer 6

1. Atherosclerosis
2. Aneurysms (abnormal areas of dilatation of an artery)
3. Inflammation, vasculitis

Question 7

What appearances of arterial thrombosis are there?

Answer 7

Mural thrombosis - large vessels
Occlusive thrombosis - medium/small vessels (image pg59)

Question 8

Why are Lines of Zahn formed? (Pg 60 image)

Answer 8

Formed due to alternating deposition of fibrin/platelets (pale) and erythrocytes (red)
Provides definitive evidence the clot formed during life

Question 9

Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in atria associated with?

Answer 9

Heart failure, atrial fibrillation

Question 10

Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in valves associated with?

Answer 10

Rheumatic fever, infective endocarditis, non-bacterial thrombotic endocarditis eg malignancy or SLE

Question 11

Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in ventricles associated with?

Answer 11

Myocardial infarction, cardiomyopathy

Question 12

How do red thrombi form?

Answer 12

Usually form in veins due to stasis of blood

Question 13

What makes up red thrombi?

Answer 13

Many enmeshed erythrocytes

Question 14

What type are red thrombi?

Answer 14

Occlusive, propagate in direction of blood flow towards the heart

Question 15

What are predisposing factors to venous thrombosis?

Answer 15

Immobility
Post-operative
Severe trauma
Myocardial infarction
Congestive heart failure
Pelvic mass
Thrombophlebitis (rare)

Question 16

Describe the 4 stages of thrombus formation (PG63J

Answer 16

A. Vasoconstriction - following an injury of the endothelium
B. Primary haemostasis - primary haemostatit clot formed mainly of a platelet plug over the area of defect
C. Secondary haemostasis - involves recruitment of thrombin and fibrin to create a more mature mesh work embedded within the platelets
D. Thrombus and antithrombotic events: mature thrombus forms with associated inflammation and trapped blood cells. Lines of Zahn can accumulate with areas of platelets and fibrin followed by areas of RBC.

Question 17

What is Virchow’s triad?

Answer 17

3 factors that promote thrombosis

Question 18

What are the 3 primary factors in Virchow’s triad?

Answer 18

Endothelial injury (eg hypercholesterolemia, inflammation)
Hypercoagulability (inherited, acquired)
Abnormal blood flow (stasis, turbulence)

Question 19

Pg64 images of thrombus development

Question 20

How is a thrombus recanalised?

Answer 20

Over time the occlusive thrombus can be recanalised. Occurs when endothelial cells proliferate and extend within the thrombus.

Question 21

What is an embolism?

Answer 21

A passage of insoluble mass (embolus) within the bloodstream and impaction at a site distant from its point of origin.

Question 22

What is the composition of an embolism?

Answer 22

Thrombus (>95%)
Others (rare): fat, air/base tumour, amniotic fluid, infective/septic material

Question 23

What are the sequence of events that occur in a pulmonary embolism? (Occlusion of pulmonary arteries)

Answer 23

1. Fragmentation of venous thrombosis
2. The thrombotic embolus is carries through progressively larger veins and the right side of the heart
3. Lodges in the pulmonary arteries, which have a smaller diameter than the embolus
   (can also arise from thrombi in RHS of the heart)

Question 24

What is the sequence of events in systemic embolism?

Answer 24

1. Fragmentation of thrombus in the left side of the heart or aorta
2. The thrombotic embolus is carried through progressively smaller arteries
3. Lodges in a branch of the aorta at a place where the diameter of the artery is less than that of the embolus

Question 25

What is ischaemia?

Answer 25

Cell injury caused by the reduced blood flow to a tissue/organ or reduced venous drainage.

Question 26

What are the causes of ischaemia?

Answer 26

Intrinsic disease of vessels
Occlusion by thrombus/embolus
External compression

Question 27

What factors determine the severity of ischaemia?

Answer 27

Speed of onset
Extent of obstruction
Anatomy of local blood supply
Pathology of collateral circulation
General factors eg cardiac state, oxygenation of blood
Vulnerability of tissue supplied to anoxia

Question 28

What is infarction?

Answer 28

Ischaemic necrosis caused by occlusion of either the arterial supply (common) or the venous drainage (less common) of a tissue/organ. I.e., end result of ischaemia.

Question 29

Shape causing an infarction

Answer 29

Tend to be wedge shaped with the occluded vessel at the apex and periphery of the organ at the base

Question 30

Why are white infarcts white and red infarcts red?

Answer 30

White colour due to lack of blood within the infarct
Red colour due to the accumulation of blood within the infarct

Question 31

How does a white infarct occur?

Answer 31

Occurs in arterial occlusion (blockage) of solid organs with end-arterial circulation where tissue density limits the seepage of blood

Question 32

Give examples of where white infarcts can occur

Answer 32

Heart, spleen, kidney

Question 33

How does a red infarct occur?

Answer 33

Occurs in loose spongy tissues in venous occlusion. Dual circulation. Previous congestion, re-established blood flow at a site of previous arterial occlusion and necrosis.

Question 34

Give examples of where red infarcts can occur

Answer 34

Lungs, small intestine, testis