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Cardiovascular System > Pathophysiology of Ischaemia and Infarction > Flashcards

Pathophysiology of Ischaemia and Infarction Flashcards

1
Q

What is ischaemia?

A

Lack of blood supply leading to inadequate O2 supply to meet the needs of the tissue/organ -> hypoxia

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2
Q

What is hypoxic hypoxia?

A

Low inspired O2 level

Normal inspired O2 but low PaO2

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3
Q

What is anaemic hypoxia?

A

Normal inspired O2 but blood abnormal

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4
Q

What is stagnant hypoxia?

A

Normal inspired O2 but abnormal delivery due to:
Local (occlusion)
Systemic (shock)

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5
Q

What is cytotoxic hypoxia?

A

Organelles cannot function properly even though they have adequate oxygen

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6
Q

What are 6 factors affecting oxygen supply?

A 
Inspired O2 
Pulmonary function 
Blood constituents 
Blood flow 
integrity of vasculature 
Tissue mechanisms
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7
Q

What are 2 factors that will increase oxygen demand?

A

Tissue itself may have different requirement

Activity of tissue above baseline

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8
Q

What can cause low inspired O2 leading to hypoxic hypoxia?

A

High altitude

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9
Q

Wh might blood flow be compromised leading to decreased O2 supply?

A

Heart failure

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10
Q

Why might the integrity of the vasculature be compromised, lead to decreased O2 supply?

A

Compression or occlusion

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11
Q

What can cause supply issues that would lead to ischaemic heart issues?

A 
Coronary artery atheroma 
Cardiac failure (decreased flow)
Pulmonary function - pul. oedema (due to LVF)
Anaemia 
Previous MI
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12
Q

What are demand issues that can cause ischaemic heart disease?

A

Heart has high intrinsic demand
Exertion
Stress

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13
Q

What is an atheroma?

A

Localised accumulation of lipid and fibrous tissue in the intima of arteries

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14
Q

What can established atheroma in coronary arteries cause?

A

Stable angina

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15
Q

What can a complicated atheroma in coronary arteries cause?

A

Unstable angina

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16
Q

What can an atheroma in the aorta cause?

A

Aneurysm - from dilatation due to weakening of the vascular wall from inflammation

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17
Q

What can an ulcerated/fissured plaque cause?

A

Thrombosis leading to ischaemia or infarction

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18
Q

What are the clinical consequences of atheroma?

A 
MI
TIA
Cerebral infarction 
AAA
Peripheral vascular disease 
Cardiac failure (CAD -> MI -> cardiac failure)
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19
Q

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?

A

16 fold decrease
Shows large effect of radius of vessels on flow and why explains why plaques significantly reduce flow and cause ischaemia

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20
Q

Give an example of where ischaemia can be chronic?

A

Sufferers of peripheral vascular disease getting claudication when walking

21
Q

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

A

Claudication in peripheral vascular disease (chronic) but can turn into an acute event

22
Q

How does ischaemia affect the biochemistry of cells?

A

Increases anaerobic metabolism, meaning less O2 is produced -> cell death

23
Q

Which cells are more affected by ischaemia?

A

Cells with high metabolic rate

24
Q

Which cells are less affected by ischaemia?

A

Cell with low metabolic rate

25
Q

What are the three general clinical effects of ischaemia?

A

Dysfunction
Pain
Physical damage

26
Q

What are the three potential outcomes of ischaemia?

A

No clinical effect
Resolution vs therapeutic intervention
Infarction

27
Q

What is infarction?

A

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

28
Q

What are the 4 possible causes of infarction?

A

Thrombosis
Embolism
Strangulation i.e. gut
Trauma - cut/ruptured vessel

29
Q

What is the scale of damage caused by the ischaemia/infarction dependent on?

A

Time period
Tissue/organ
Pattern of blood supply
Previous disease

30
Q

How does infarction cause necrosis?

A

More anaerobic metabolism therefore less O2 produced -> cell death -> release of enzymes -> breakdown of tissue

31
Q

What is coagulative necrosis?

A

Cell death is caused by lack of blood flow, and the cells become dry, hard and white
I.e. heart, lung

32
Q

What is colliquitive necrosis?

A

Transformation of the tissue into a liquid viscous mass

I.e. brain

33
Q

Describe the sequence of events in necrosis

A

Coronary arterial obstruction -> decrease blood flow to region of myocardium -> ischaemia causing rapid myocardial dysfunction -> myocyte death

34
Q

What occurs in the first seconds of myocardial ischaemia?

A

Anaerobic metabolism causing ATP depletion

35
Q

How long is severe ischaemia and is it reversible?

A

20-30mins and causes irreversible damage

36
Q

What occurs in the first 2mins of myocardial ischaemia?

A

Loss of myocardial contractility (leading to heart failure)

37
Q

What ultrastructural changes occur in the first few minutes of myocardial ischaemia?

A

Myofibrillar relaxation
Glycogen depletion
Cell and mitochondrial swelling

38
Q

What happens in the first 20-40mins of infarction?

A

Myocyte necrosis

39
Q

What happens in the first hour after infarction?

A

Injury to the microvascular

40
Q

Describe the appearance of infarcts in the 24hrs after infarction

A

No change visually

Up to 12hrs after - swollen mitochondria on electron microscopy

41
Q

Describe the appearance of infarcts 24-48hrs after infarction

A

Pale infarct: myocardium, spleen kidney, solid tissues

Red infarct: lung, liver - loose tissues, previously congested tissue

Microscopically: acute inflammation initially at edge of infarct, loss of specialised cell features

42
Q

Describe the appearance of infarcts 72hrs after infarction

A

Macroscopically: pale - yellow/white and red periphery and no change to red infarct

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

43
Q

What is the end result appearance of infarcts?

A

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

Reperfusion injury

44
Q

What is a repercussion injury?

A

Tissue damage caused when blood supply returns to tissue after a period of ischemia or lack of oxygen

45
Q

What is the process of repair after infarction?

A
  1. Cell death
  2. Acute inflammation
  3. Macrophage phagocytosis of dead cells
  4. Granulation tissue
  5. Collagen deposition (fibrosis)
  6. Scar formation
46
Q

What is a transmural infarction?

A

Ischaemic necrosis affects the full thickness of the myocardium

47
Q

What is a subendocardial infarction?

A

Ischaemic necrosis limited to a zone under the endocardium

48
Q

What are acute infarcts classified by?

A

Whether there is elevation of the ST segment on the ECG

49
Q

List some complications of myocardial infarctions

A 
Sudden death 
Arrhythmias 
Angina
Heart failure 
Rupture of wall, septum, papillary muscle due to weakening wall from necrosis
Pulmonary embolism secondary to DVT
Papillary muscle dysfunction/rupture causing mitral incompetence 
Mural thrombosis 
Ventricular aneurysms 
Dresslers syndrome

Cardiovascular System (37 decks)

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