Thrombosis, embolism, ischaemia and infarction

Question 1

What is the definition of thrombosis?

Answer 1

formation of a solid mass
form the constituents of blood
within the vascular system during life (different to a simple blood clot)

Question 2

What is the mechanism behind thrombosis?

Answer 2

exaggeration of normal haemostatic mechanisms:

1) coagulation system - formation of blood clot
2) platelets - adhesion, aggregation, secretion
3) vascular endothelium - promotion/inhibition of 1 & 2, protection of circulating blood from highly thrombogenic subendothelium

Question 3

What is virchow’s triad?

Answer 3

1) changes in vessel wall - endothelial damage
2) changes in blood flow - stasis, turbulence
3) changes in blood composition - many poorly defined (polycythaemia, nephrotic synrome, malignancy, oral contraceptive pill)

Question 4

What is the composition and appearance of thrombi?

Answer 4

blood clots + platelets
= variable proportions depending on speed of blood flow

characteristic laminations - lines of zahn

1) arterial/cardiac (rapid flow)
- mainly platelets (pale)
- mural or occlusive (depending on size of vessel)

2) venous (slow flow)
- mainly blood clot (red)
- usually occlusive

Question 5

What are the sites where thrombosis usually occurs?

Answer 5

heart
arteries
veins

Question 6

What are examples of cardiac thrombosis?

Answer 6

1) atria
- most common in appendages
- associated with HF and AF

2) valves (vegetations)
- rheumatic fever (Sterile), infective endocarditis (infective), non-bacterial thombotic endocarditis (sterile - malignancy, SLE)

3) ventricles
- mural thrombosis
- associated MI and cardiomyopathy

Question 7

What are the causes and appearance of arterial thrombosis ?

Answer 7

causes:
- atherosclerosis, aneurysms, inflammation (vasculitis)

appearance: mural thrombosis (large vessels), occlusive thrombosis (medium/small vessels)

Question 8

What are the predisposing factors to venous thrombosis?

Answer 8

immobility 
post op
severe trauma
MI
congestive HF
pelvic mass (inc pregnancy)
thrombophlebitis

Question 9

What are the pathological features of venous thrombosis?

Answer 9

usually occlusive

propagation

Question 10

What is the sequelae of thrombosis?

Answer 10

1) resolution = dissolution of clot by fibrinolysis (venous thrombi)
2) organisation = ingrowth of fibroblasts, capillaries, phagocytes (granulation tissue)
3) recanalisation = restoration of original lumen, fibrosis = formation of webs, cords

Question 11

What are the main complications of thrombosis?

Answer 11

arteries - ischaemia/infarction

veins/heart = embolism

Question 12

What is the definition of embolism?

Answer 12

passage of insoluble mass (embolus)

within the blood stream and impaction at a site distant from its point of origin

Question 13

What is the composition of emboli?

Answer 13

1) thrombus (>95%)

2) other (rare) - fat, gas/air, tumour, amniotic fluid, infective material

Question 14

What are the sites of impaction of emboli?

Answer 14

1) pulmonary arteries = thrombi from veins, to right side of heart
2) systemic arteries = thrombi from left side of heart and aorta

Question 15

What is the definition of ischaemia?

Answer 15

reduced blood supply to tissue or organ

harmful effects due to hypoxia

Question 16

What are the causes of ischaemia?

Answer 16

1) intrinsic disease of vessels
2) occlusion by thrombus/embolus
3) external compression

Question 17

What factors determine the severity of ischaemia?

Answer 17

1) speed of onset
2) extent of obstruction
3) anatomy of local blood supply = end arteries, parallel arteries, inter-arterial branches
4) pathology of collateral circulation
5) general factors - cardiac state, oxygenation of blood
6) vulnerability of tissue supplied to anoxia

Question 18

What is the definition of infarction?

Answer 18

death of tissue due to ischaemia

usually arterial occlusion, occasionally venous

Question 19

How are infarctions classified?

Answer 19

shape - wedge shaped or other
colour - white or red
infection - bland or septic

Question 20

What are the 4 stages of infarction?

Answer 20

1) necrosis = usually coagulative - 6-12 hours
2) acute inflammation = congestion, oedema, migration of polymorphs - 24 hours - 7 days
3) organisation = ingrowth of capillaries, macrophages, fibroblasts - 3 days - 2 weeks
4) scar formation = deposition of collagen polymerisation - 2 weeks - 3 months

Question 21

Why are the stages of infarction important?

Answer 21

determining the age of infarcts

understanding complications of infarction

Question 22

What are the sources of PE?

Answer 22

1) dvt - >95%
2) other veins - pelvic, iliac, vena cava
3) right side of heart

Question 23

What are the consequences of PE?

Answer 23

1) Sudden death - massive embolism
2) pulmonary infarction - pulmonary venous congestion, haemorrhagic, peripheral, wedge-shaped
3) pulmonary hypertension - recurrent PE
4) asymptomatic - complete resolution (up to 60-80%)

Question 24

What are the common and rare sources of systemic emboli?

Answer 24

common

• left atrium - AF
• valves - infective endocarditis
• left ventricle - MI
• aorta - atherosclerosis

rare

• paradoxical embolus - atrial septal defect
• atrial myxoma

Question 25

What is the clinical relevance of knowing the source of a systemic emboli?

Answer 25

patient presenting with complications of embolism e.g. cerebral infarction consider predisposing factors and treat to prevent further episodes

Question 26

What are the 2 main patterns of MI?

Answer 26

regional (transmural) >90% - sharply localised, thrombosis of main coronary artery branch subendocardial <10% - poorly localised, severe triple vessel atheroma

Question 27

What is the definition of gangrene?

Answer 27

necrosis (tissue death) with superadded bacterial infection

Question 28

When do fat embolisms occur?

Answer 28

bone fractures and other soft tissue trauma pulmonary circulation => dyspnoea, haemoptysis systemic circulation => widespread microemboli (esp brain) mortality = 10-15%

Question 29

What are the causes and effects of air/gas embolism?

Answer 29

causes = venous rupture, accidental infusion, decompression sickness Effects = nil (small amounts), sudden death (>200ml), microemboli

Question 30

What happens and what is the prognosis of amniotic fluid embolism?

Answer 30

rare - 1 in 50,000 deliveries high mortality >80% rupture of uterine veins during labour impaction of amniotic contents in pulmonary vessels