Pathophysiology of Ischaemia and Infarction

Question 1

Define Ischaemia

Answer 1

Need oxygen to function
Relative lack of blood supply to tissue/organ leading to inadequate O2 supply to meet needs of tissue/organ (hypoxia)

Question 2

Define hypoxia

Answer 2

(Relative lack of blood supply to tissue/organ leading to) inadequate O2 supply to meet needs of tissue/organ

Question 3

Define infarction

Answer 3

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

Question 4

Explain the relationship between atheroma and ischemia

Answer 4

Established atheroma in coronary artery - stable angina

Complicated atheroma in coronary artery - unstable angina

Ulcerated/fissured plaques –> thrombosis –> ischaemia/infarction

Atheroma in aorta –> aneurysm

Question 5

Describe the consequences of ischaemia

Answer 5

MI
TIA
Cerebral infarction
Abdominal aortic aneurysm
Peripheral vascular disease
Cardiac failure

Coronary artery disease –> MI –> cardiac failure

Question 6

What are the supply and demand issues affecting the heart and coronary blood flow

Answer 6

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

DEMAND ISSUES
- heart has high intrinsic demand,
- exertion/stress

Question 7

Describe the process of infarction

Answer 7

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

Scale of damage of ischaemia/infarction dependent on several factors:
- Time period
- Tissue/organ
- Pattern of blood supply
- Previous disease

Question 8

What is the difference between subendocardial and transmural infarction of myocardium

Answer 8

Transmural infarction: ischaemic necrosis affects full thickness of the myocardium

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

Histological features are the same

Question 9

What is the clinical significance of the two types of infarct

Question 10

List the effect of infarction

Answer 10

Site dependent – within body and organ

Size of infarct

Death, dysfunction (pain)

Contribution of previous disease/infarction

Question 11

What is the reparative process involved in myocardial infarction

Answer 11

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

Question 12

What are the four types of hypoxia?

Answer 12

HYPOXIC
(a) Low inspired O2 levels
(b) Normal inspired O2 but low PaO2

ANAEMIC
- Normal inspired O2 but abnormal blood

STAGNANT
- Normal inspired O2 but abnormal delivery
(a) Local
(b) Systemic

CYTOTOXIC
- Normal inspired O2 but abnormal at tissue level

Question 13

Factors affecting oxygen supply

Answer 13

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

Question 14

Factors affecting oxygen demand

Answer 14

1. Tissue itself - different tissues have different requirements
2. Activity of tissue above baseline value

Question 15

MYOCARDIAL ISCHAEMIA

Answer 15

• Anaerobic metabolism, onset of ATP depletion
• Loss of myocardial contractility ( heart failure)
• Ultrastructural changes