pathology of ischaemia and infarction

Question 1

what is ischaemia?

Answer 1

Relative lack of blood supply to tissue/organ leading to inadequate O2 supply to meet needs of tissue/organ: hypoxia

Question 2

what is hypoxic?

Answer 2

Low inspired O2 level

(b) Normal inspired O2 but low PaO2

Question 3

what is anaemic?

Answer 3

Normal inspired O2 but blood abnormal

Question 4

what is stagnant?

Answer 4

Normal inspired O2 but abnormal delivery
Local e.g. occlusion of vessel
Systemic e.g. shock

Question 5

what is cytoxic?

Answer 5

Normal inspired O2 but abnormal at tissue level

Question 6

factors affecting oxygen supply?

Answer 6

Inspired O2

2. Pulmonary function
3. Blood constituents
4. Blood flow
5. Integrity of vasculature
6. Tissue mechanisms

Question 7

factors affecting oxygen demand?

Answer 7

Tissue itself - different tissues have different requirements

2. Activity of tissue above baseline value

Question 8

what are the supply issues for ischaemic heart disease?

Answer 8

coronary artery atheroma, cardiac failure (flow), pulmonary function – other disease or pulmonary oedema (LVF), anaemia, previous MI

Question 9

what are the demand issues for ischaemic heart disease?

Answer 9

heart has high intrinsic demand, exertion/stress

Question 10

what is atheroma/atherosclerosis?

Answer 10

Localised accumulation of lipid and fibrous tissue in intima of arteries

Question 11

whats the correlation between atheroma and stable angina?

Answer 11

established atheroma in coronary artery

Question 12

whats the correlation between atheroma and unstable angina?

Answer 12

Complicated atheroma in coronary artery

Question 13

what would an atheroma in aorta be?

Answer 13

aneurysm

Question 14

what would ulcerated/fissured plaques be?

Answer 14

thrombosis which could lead to ischaemia/infarction

Question 15

what are the effects of ischaemia functionally ?

Answer 15

Blood/O2 supply fails to meet demand due to supply; demand; or both
Related to rate of onset

Question 16

what are the effects of ischaemia biochemically?

Answer 16

Normal aerobic metabolism
glucose+36ADP+36Pi+36H++6O2 6CO2+36ATP+42H2O
Anaerobic metabolism
glucose+2Pi+2ADP 2lactate+2ATP+2H2O
L-lactatepyruvate
Pyruvate+NAD++CoAacetylCoA+CO2+NADH
decreased O2 anaerobic metabolism leads to cell death

Question 17

what is infarction?

Answer 17

Ischaemic necrosis within a tissue/organ in living body produced by occlusion of either the arterial supply or venous drainage

Question 18

whats the aetiology of infraction?

Answer 18

cessation of blood flow
For example:
1. Thrombosis
2. Embolism
3. Strangulation e.g. gut
4. Trauma - cut/ruptured vessel

Question 19

what is the scale of infarction dependent on?

Answer 19

Time period
Tissue/organ
Pattern of blood supply
Previous disease

Question 20

what happens with an infarction?

Answer 20

Anaerobic metabolism goes to cell death goes to liberation of enzymes goes to breakdown of tissue

Coagulative necrosis e.g. heart, lung

Question 21

how long does anaerobic metabolism, onset of ATP depletion take

Answer 21

seconds

Question 22

how long does loss of myocardial contractility leading to heart failure

Answer 22

over 2 minutes

Question 23

how long does myocyte necrosis take?

Answer 23

20-40 minutes

Question 24

how long does injury to the microvasculature take?

Answer 24

over 1 hour

Question 25

what visual changes can you see in less than 24 hours?

Answer 25

No change on visual inspection | A few hours to 12 hours post insult, see swollen mitochondria on Electron Microscopy

Question 26

what visual changes can you see in less than 24 - 48 hours?

Answer 26

Pale infarct: e.g. myocardium, spleen, kidney Solid tissues Red infarct: e.g. in lung, liver Loose tissues, previously congested tissue; second/continuing blood supply, venous occlusion Microscopically: acute inflammation initially at edge of infarct; loss of specialised cell features

Question 27

what visual changes can you see in less than 72 hours ?

Answer 27

Macroscopically: Pale infarct - yellow/white and red periphery Red infarct - little change Microscopically: chronic inflammation; macrophages remove debris; granulation tissue; fibrosis

Question 28

whats the end result of infarcts?

Answer 28

Scar replaces area of tissue damage Shape depends on territory of occluded vessel Reperfusion Injury

Question 29

what is the repartive process of MI

Answer 29

``` Cell death Acute inflammation Macrophage phagocytosis of dead cells Granulation tissue Collagen deposition (fibrosis) Scar formation ```

Question 30

what would you see in 4-12 hours in myocardial infarction?

Answer 30

Early coagulation necrosis, oedema, haemorrhage

Question 31

what would you see in 12-24 hours in myocardial infarction?

Answer 31

Ongoing coagulation necrosis, myocyte changes, early neutrophilic infiltrate

Question 32

what would you see in 1-3 days in myocardial infarction?

Answer 32

Coagulation necrosis, loss of nuclei and striations, brisk neutrophilic infiltrate

Question 33

what would you see in 3-7 days in myocardial infarction?

Answer 33

Disintegration of dead myofibres, dying neutrophils, early phagocytosis

Question 34

what would you see in 7-10 days | in myocardial infarction?

Answer 34

Well developed phagocytosis, granulation tissue at margins

Question 35

what would you see in 10-14 days | in myocardial infarction?

Answer 35

Well established granulation tissue with new blood vessels and collagen deposition

Question 36

what would you see in 2-8 weeks in myocardial infarction?

Answer 36

Increased collagen deposition, decreased cellularity

Question 37

what would you see in >2 months | in myocardial infarction?

Answer 37

Dense collagenous scar

Question 38

what is Transmural infarction

Answer 38

: ischaemic necrosis affects full thickness of the myocardium

Question 39

what is Subendocardial infarction

Answer 39

ischaemic necrosis mostly limited to a zone of myocardium under the endocardial lining of the heart

Question 40

what are acute infarcts classified as?

Answer 40

whether there is elevation of the ST segment on the ECG

Question 41

what would a 'If no ST segment elevation but a significantly elevated serum troponin level' mean?

Answer 41

non-STEMI

Question 42

what are the complications of myocardial infarction?

Answer 42

Immediate; early; late Sudden death; arrhythmias; angina; cardiac failure; cardiac rupture - ventricular wall, septum, papillary muscle; reinfarction; pericarditis; pulmonary embolism secondary to DVT; papillary muscle dysfunction - necrosis/rupture mitral incompetence; mural thrombosis; ventricular aneurysm; Dressler's syndrome