pathophysiology of ischaema and infarction

Question 1

what is ischaemia?

Answer 1

relative lack of blood supply to organ/tissue leading to inadequate oxygen supply to meet needs of tissue/organ

Question 2

what are the 4 ways that hypoxia can occur?

Answer 2

1. low inspired oxygen level or normal inspired oxygen but low PaO2
   2 anaemia-normal inspired oxygen but blood abnormal
2. stagnation- normal inspired oxygen but abnormal delivery
3. cytotoxic- normal oxygen inspired but abnormal at tissue level

Question 3

what can cause low in inspired oxygen levels leading to hypoxia?

Answer 3

high altitude

Question 4

what can lead to local stagnation of blood flow leading to hypoxia?

Answer 4

occlusion of vessel

Question 5

what can causes systemic stagnation of blood flow leading to hypoxia?

Answer 5

shock

Question 6

what is cytotoxic hypoxia?

Answer 6

organelles cannot function properly even though they have adequate oxygen

Question 7

what are the factors that affect oxygen supply?

Answer 7

1. Inspired O2
2. Pulmonary function
3. Blood constituents
4. Blood flow
5. Integrity of vasculature
6. Tissue mechanisms

Question 8

when might blood flow be compromised, decreasing oxygen supply?

Answer 8

when there is heart failure

Question 9

when might the integrity of vasculature be compromised, decreasing oxygen supply?

Answer 9

occlusion/compression of vessels

Question 10

what are the 2 factors that affect the oxygen demand of a tissue?

Answer 10

the type of tissue

activity of the tissue above the baseline

Question 11

what are the supply issues that can cause ischaemic heart disease?

Answer 11

coronary artery atheroma
cardiac failure
pulmonary function- pulmonary oedema (from LVF)
anaemia
previous MI

Question 12

what are demand issues that can cause ischaemic heart disease?

Answer 12

heart has high intrinsic demand

exertion/stress

Question 13

how can atherosclerosis cause stable angina?

Answer 13

when it is established and doesnt occlude the coronary artery so much as to cause inadequate oxygen supply at rest. however on exertion oxygen supply becomes inadequate

Question 14

how can atherosclerosis cause unstable angina?

Answer 14

when the atheromatous plaque in the coronary artery is complicated and so causes inadequate delivery of oxygen at rest

Question 15

what do ulcerated and fissure plaques in the coronary artery lead to?

Answer 15

thombosis then ischaemia or infarction

Question 16

how does atheroma cause an aortic aneurysm?

Answer 16

dilatation of the aorta due to weakening of the vascular wall from inflammation

Question 17

what conditions can atheromatous plaques lead to?

Answer 17

MI
TIA
Cerebral infarction
abdominal aortic aneurysm
peripheral vascular disease
cardiac failure (could be from MI)

Question 18

a reduction in radius of an artery from 4 to 2 will cause a decrease of what in blood flow? and how does this explain how plaques cause ischaemia?

Answer 18

16 fold decrease.
this highlights the large effect of radius of vessels on flow. this explains why plaques significantly reduce flow and cause ischaemia

Question 19

give an example of where ischaemia can be chronic?

Answer 19

sufferers of peripheral vascular disease getting claudication when walking

Question 20

give an example of when ischaenia can be acute-on-chronic ?

Answer 20

claudication in peripheral vascular disease (chronic) but can turn into and acute event

Question 21

how does ischaemia affect the biochemistry of cells?

Answer 21

causes cells to metabolise more by anaerobic respiration. So lactate builds up on cells, causing acid-bace imbalance and leads to cell death

Question 22

which cells are more affected by ischaemia?

Answer 22

those with high metabolic rate, eg. renal tubule, myocyte, neurons

Question 23

which cells are less affected by ischaemia?

Answer 23

those with a slower metabolic rate

Question 24

what are the three general clinical effects of ischaemia?

Answer 24

• dysfunction
• pain
• physical damage

Question 25

what dysfunction can ischaemia cause in the heart?

Answer 25

if it is next to the SA node then there is the chance that it may lead to cardiac arrhythmia

Question 26

how does ischaemia cause heart pain/

Answer 26

due to pH changes and bracycardia

Question 27

what are the three potential outcomes of ischaemia?

Answer 27

- no clinical effect - resolution (normally need therapeutic intervention) - infarction

Question 28

what is infarction?

Answer 28

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

Question 29

what are the 4 possible causes of infarction?

Answer 29

1. thrombosis 2. embolism 3. strangulation 4. trauma-cut/ruptured vessel

Question 30

if an infarction occurs for a short time, how is the long-term damage different from if it was for a long time?

Answer 30

it is less

Question 31

what are the factors that determine the scale of damage from ischaemia or infarction?

Answer 31

- Time period - Tissue/organ - Pattern of blood supply - Previous disease

Question 32

what is coagulative necrosis?

Answer 32

necrosis in which the organ maintains its shape after necrosis

Question 33

what is colliquitive necrosis?

Answer 33

necrosis in which the tissue loses its gross structure as there is loss of connective tissue

Question 34

describe the sequence of events in necrosis

Answer 34

1. Anaerobic metabolism 2. cell death 3. liberation of enzymes 4. breakdown of tissue

Question 35

give examples of tissue that undergo coagulative necrosis?

Answer 35

heart, lung

Question 36

give examples of a tissue that undergo colliquitive necrosis?

Answer 36

brain

Question 37

how long is severe ischaemia and is it reversible?

Answer 37

20-30 minutes | irreversible damage

Question 38

what happens in the first seconds of myocardial ischaemia?

Answer 38

anaerobic matabolism causes ATP depletion

Question 39

what happens in the first 2 minutes of myocardial ischaemia?

Answer 39

loss of myocardial contractility leading to heart failure

Question 40

what happens after the first 2 minutes of myocardial ischaemia?

Answer 40

- ultrastructural changes: - myofibrillar relaxation - glycogen depletion - cell and mitochondial swelling

Question 41

after how long of ischaemia is there injury to the microvasculature of the heart?

Answer 41

>1 hour

Question 42

after 24-48 hours what is the appearance of an infarct in dense tissues such as the myocardium, spleen, kidney solid tissues

Answer 42

pale

Question 43

after 24-48 hours what is the appearance of an infarct in loose tissues such as the lung, liver and perviously congested tissues?

Answer 43

red

Question 44

under the microscope what can be seen around the edge of infarcts at 24-48 hours?

Answer 44

inflammatory cells such as neutrophils

Question 45

under the microscope what can be seen i infarcts at 72 hours after event?

Answer 45

chronic inflammation: - macrophages remove debris - granulation tissue - fibrosis

Question 46

what is the end result of infarction?

Answer 46

scar replaces area of tissue damage | reperfusion injury

Question 47

what is reperfusion injury?

Answer 47

after a period of ischaemia blood reperfuses the tissue. | this causes inflammation and further damage to the tissue as there inflammation and oxidative injury

Question 48

what are the reparative processes of mysocardial infarction?

Answer 48

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

Question 49

what is a transmural myocardial infarction?

Answer 49

ischaemic necrosis affects full thickness of the myocardium

Question 50

what is a subendocardial infarction?

Answer 50

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

Question 51

what sort of MI is a non-STEMI most likely to be?

Answer 51

subendocardial infarct

Question 52

what sort of myocardial infarction is likely to have occurred if there is no ST elevation and elevated serum troponin level?

Answer 52

non-STEMI

Question 53

what are some of the complication of myocardial infarction?

Answer 53

``` sudden death arrythmias angina cardiac failure cardiac rupture-ventricular wall, septum, papillary muscle reinfarction pericarditis pulmonary embolism secondary to DVT -papillary muscle dysfunction from necrosis or rupture causing mitral incompetence mural thrombosis ventricular aneurysm dressler's syndrome ```

Question 54

what is dressler's syndrome?

Answer 54

Dressler syndrome is a secondary form of pericarditis that occurs in the setting of injury to the heart or the pericardium

Question 55

what does papillary muscle dysfunction lead to?

Answer 55

usually mitral (but can be tricuspid) incompetence