Ischaemia and Infarction

Question 1

What is ischaemia

Answer 1

Relative lack of blood supply to tissue/organ leading to inadequate oxygen supply to meet demands of tissue/organ

Question 2

Name the four types of hypoxia

Answer 2

Hypoxic hypoxia
Anemic hypoxia
Stagnant hypoxia
Cytotoxic hypoxia

Question 3

How does hypoxia arise in hypoxic hypoxia

Answer 3

Low inspired oxygen level or normal inspired oxygen but low PaO2

Question 4

How does anaemic hypoxia arise

Answer 4

Abnormal blood

Question 5

How does stagnant hypoxia arise

Answer 5

Abnormal delivery of oxygen either locally (eg occlusion) or systemic (eg shock)

Question 6

How does cytotoxic hypoxia arise

Answer 6

Abnormal at tissue level

Question 7

What 6 factors affect oxygen supply

Answer 7

Inspired oxygen
Pulmonary function
Blood constituents
Blood flow
Integrity of vasculature
Tissue mechanisms

Question 8

2 factors affecting oxygen demand

Answer 8

Tissue itself - some require more oxygen than others

Activity of tissue above baseline

Question 9

In terms of the factors that affect oxygen supply, what specific problems can lead to ischaemic heart disease?

Answer 9

Coronary artery atheroma
Cardiac failure (flow)
Pulmonary function - disease/pulmonary oedema (LVF)
Anaemia
Previous MI

Question 10

What demand issues may lead to ischaemic heart disease

Answer 10

Heart has high intrinsic demand, especially on exertion or stress

Question 11

What is an atheroma

Answer 11

Localised accumulation of lipid and fibrous issue in intima of arteries

Question 12

What do the following lead to clinically:

1. established atheroma
2. complicated atheroma
3. ulcerated/fissured plaques
4. atheroma in aorta

Answer 12

1. stable angina
2. unstable angina
3. thrombosis and then ischaemia or infarction
4. aneurysm

Question 13

6 clinical consequences of atheroma throughout the body

Answer 13

MI - cardiac failure
Transient ischaemic attack
Cerebral infarction
Abdominal aortic aneurysm
Peripheral vascular disease

Question 14

What are the 6 categories for effects of ischaemia

Answer 14

functional 
general
biochemical
cellular
clinical 
outcome

Question 15

What are the functional effects of ischaemia

Answer 15

Blood oxygen supply fails to meet demand

Question 16

What are the three ways the general effects of ischaemia can be described

Answer 16

Can be acute, chronic or acute on chronic

Question 17

What are the biochemical effects of ischaemia

Answer 17

Aerobic metabolism changes to anaerobic metabolism. Increased lactate and pyruvate. Not enough oxygen for cells and cells die.

Question 18

What are the cellular effects of ischaemia?

Answer 18

Different cells have variable oxygen requirement so are variably susceptible to ischaemia eg those with high metabolic rate

Question 19

Three clinical effects of ischaemia

Answer 19

Dysfunction
Pain
Physical damage

Question 20

Three possible outcomes of ischaemia

Answer 20

No clinical effect
Resolution versus therapeutic intervention
Infarction

Question 21

Definition of infarction

Answer 21

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

Question 22

Four examples of aetiology of infarction

Answer 22

Thrombosis
Embolism
Strangulation
Trauma

Question 23

What four factors is the scale of damage of ischaemia/infarction dependent on

Answer 23

time period
tissue/organ
pattern of blood supply
previous disease

Question 24

What are the two types of necrosis

Answer 24

Coagulative necrosis

Colliquitive necrosis

Question 25

What organs experience coagulative necrosis

Answer 25

Heart | Lung

Question 26

What organ has colliquitive necrosis

Answer 26

brain

Question 27

What happens in seconds in myocardial ischaemia

Answer 27

anaerobic metabolism | onset of ATP depletion

Question 28

What happens in less than 2 minutes

Answer 28

Loss of myocardial contractility

Question 29

How long until myocyte necrosis

Answer 29

20-40 minutes

Question 30

How long until injury to microvasculature

Answer 30

over an hour

Question 31

What is the appearance of the infarct in less than 24 hours

Answer 31

no change on visual inspection | swollen mitochondria on electron microscopy

Question 32

What is the appearance of the infarct 24-48 hours

Answer 32

Pale infarct red infarct microscopically - acute inflammation at edge of infarct, loss of specialised features

Question 33

What kind of tissues appear as pale infarcts

Answer 33

Solid tissues eg. myocardium, spleen, kidney

Question 34

What kind of tissues appear as red infarcts

Answer 34

Loose tissue eg. lung, liver Previously congested tissue Second, continuing blood supply Venous occlusion

Question 35

What changes to pale infarct 72 hours onwards

Answer 35

Yellow/white and red periphery

Question 36

What changes to red infarct 72 hours onwards

Answer 36

little change

Question 37

What changes microscopically 72 hours onwards

Answer 37

Chronic inflammation, macrophages remove debris, granulation tissue, fibrosis

Question 38

6 steps of reparative process of myocardial infarction

Answer 38

1. cell death 2. acute inflammation 3. macrophage phagocytosis dead cells 4. granulation tissue 5. collagen deposition 6. scar formation

Question 39

What are the two types of infarction

Answer 39

Transmural - affects full thickness of myocardium | Subendocardial - limited to zone under endocardial lining

Question 40

Complications of myocardial infarction (there are many)

Answer 40

``` 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 ```