Ischaemia and Infarction

Question 1

What is the definition of Infarction?

Answer 1

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

Question 2

What is the definition of Ischaemia?

Answer 2

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

Question 3

What are the four types of hypoxia?

Answer 3

Hypoxic - high altitudes, low partial pressure of O2
Anaemic - low haemoglobin
Stagnant - abnormal delivery of O2, local (occlusion), systematic (shock, hypotension)
Cytotoxic - respiring organelles don’t work properly

Question 4

What are the factors affecting O2 supply?

Answer 4

1. Inspired O2
2. Pulmonary function- oedema ?
3. Blood constituents – enough haemoglobin
4. Blood flow – turbulence, stasis
5. Integrity of vasculature – tumour, atheroma
6. Tissue mechanisms – cells have to work properly, organelles
7. Previous MI

Question 5

What factors could effect the O2 demand?

Answer 5

1. exertion eg. exercise, stress

2. heart has a high intrinsic demand of oxygen

Question 6

Is there a clinical correlation between atheroma and ischaemia?

Answer 6

established atheroma = stable angina
complicated atheroma (fissuring, rupture) = unstable angina

complicated atheroma -> thrombosis -> ischaemia/infarction

Question 7

name six clinical consequences of ischaemia.

Answer 7

¥	MI 
¥	TIA – symptoms of a stroke lasting for less than 24 hours
¥	Cerebral infarction
¥	Abdominal aortic aneurysm
¥	Peripheral vascular disease
¥	Cardiac failure

Question 8

What are the functionally effects of ischaemia?

Answer 8

Blood/O2 supply fails to meet demand due to decreased supply; increased demand

Question 9

What are the general effects of ischaemia?

Answer 9

¥ Acute – obvious signs, breathlessness, chest pain

¥ Chronic – insidious signs

Question 10

What are the biochemical effects of ischaemia?

Answer 10

decrease of O2 
more anaerobic respiration 
acid base balance is altered 
pH decreases 
this causes cell death

Question 11

What are the cellular effects of ischaemia?

Answer 11

¥ Cells with high metabolic rate – greatly and quickly effected (require more O2)
¥ Cells with low metabolic rate - less effected

Question 12

What causes infarction??

Answer 12

cessation of blood flow

Question 13

Name four ways which can stop blood flow.

Answer 13

1. Thrombosis
2. Embolism
3. Strangulation e.g. gut twisted
4. Trauma - cut/ruptured vessel

Question 14

What does the scale of damage form infarction depend on?

Answer 14

1. Time period
2. Tissue/organ (site in the body)
3. Pattern of blood supply – number of arteries supplying the area
4. Previous disease
5. Size of infarction

Question 15

State the sequence of events that cause infarction.

Answer 15

coronary artery obstruction (atheroma, thrombosis)
decreased blood flow 
ischaemia 
anaerobic respiration (pH decreases) 
increased cell death 
liberation of enzymes 
breakdown of tissue

Question 16

Name the two types of tissue necrosis in the heart and in the brain.

Answer 16

Coagulative necrosis e.g. heart, lung

Colliquitive necrosis e.g. brain (more liquid)

Question 17

What is a myocardial infarction?

Answer 17

When blood flow is blocked in the coronary arteries supplying the heart.
This means that oxygen cannot reach the myocardial cells and causes cell death and therefore heart failure and ultimately death as the blood cannot be pumped around the body properly.

Question 18

State the sequence and time frame of a MI

Answer 18

1. anaerobic respiration (ATP depletion) = seconds

2. loss of myocardial contraction = 1 hour

Question 19

What is the appearance of a MI at:

Question 20

Following on from the question before:

What is the sequence of events of healing process of a MI

Answer 20

1. Cell death
2. Acute inflammation
3. Macrophage phagocytosis of dead cells
4. Granulation tissue
5. Collagen deposition (fibrosis tissue)
6. Scar formation (fibrosis tissue becomes old and well established

Question 21

What are the two types of MI that affect different thicknesses of the myocardium?

Answer 21

Transmural infarction - effects full thickness of myocardium

Subendocardial infarction - just under endothelium

Question 22

Which repair time is shorter..? transmural or subendocardial?

Answer 22

Subendocardial

Question 23

what are some complications of MI

Answer 23

¥	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 – secondary form of pericarditis that occurs in the setting of injury to the heart or the pericardium

Question 24

Does ST elevation correlate with subendocardial or transmural infarct?

Answer 24

transmural