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Cardiovascular block > Pathophysiology of ischaemia and infarction > Flashcards

Pathophysiology of ischaemia and infarction Flashcards

1
Q

What is ischaemia ?

A

Reduced blood flow to organs/ tissues

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2
Q

What is hypoxia ?

A

Inadequate oxygen supply to meet the needs of tissue/ organs ?

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3
Q

What is hypoxic hypoxia ?

A

Low inspired O2 levels

Normal inspired o2 but low PaCO2

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4
Q

What is anaemic hypoxia ?

A

Normal inspired O2 but blood abnormal;

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5
Q

What is stagnant hypoxia ?

A

Normal inspired O2 but abnormal delivery
Local e.g. occlusion of artery
Systemic e.g. shock

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6
Q

What is cytotoxic hypoxia ?

A

Normal inspired O2 but abnormal at tissue level

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7
Q

What are the factors affecting O2 supply ?

A 
Inspired O2
Pulmonary function
Blood constituents
Blood flow
Integrity of vasculature
Tissue mechanisms
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8
Q

What are the factors affecting O2 demand ?

A

Tissue itself- different tissues have different requirements

Activity of tissue above baseline value

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9
Q

What are the supply issues with iscahmic heart disease ?

A

Coronary artery atheroma
Cardiac failure (flow)
Pulmonary function- other disease or pulmonary oedema (LVF)
Anaemia, previous MI

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10
Q

What are the demand issues with ischaemic heart disease ?

A

Heart has high intrinsic demand

exertion/ stress

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11
Q

What is an atheroma/atherosclerosis ?

A

Localised accumulation of lipid and fibrous tissue in intima of arteries

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12
Q

What is the clinical correlation with established atheroma in coronary artery ?

A

Stable angina

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13
Q

What is the clinical consequence of complicated atheroma in coronary artery ?

A

Unstable angina

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14
Q

What is the clinical correlation of an ulcerated/fissured plaque ?

A

Leads to thrombosis, then leads to ischaemia and infarction

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15
Q

What are the clinical consequences of atheroma ?

A 
MI
TIA
Cerebral infacrtion
Abdominal aortic aneurysm 
Peripheral vascular diease
Cardiac failure 
Coronary artery disease-> MI-> cardiac failure
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16
Q

What are the effects of atheroma on blood flow ?

A

Changes in vessel wall-> thrombosis
Poiseuille’s formula- R= 8ηl/πr2
Blood flow- Q = ∆P/R

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17
Q

What are the functional effects of ischaemia ?

A

Blood/ O2 supply fails to meet demand due to decreased supply; increased demand; or both
Related to rate of onset

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18
Q

What are the general effects of ischaemia ?

A

Acute
Chronic
Acute-on-chronic

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19
Q

What are the biochemical effects of ischaemia ?

A
  • Normal aerobic metabolism
    glucose+36ADP+36Pi+36H++6O2 ®6CO2+36ATP+42H2O
    • Anaerobic metabolism
      glucose+2Pi+2ADP ®2lactate+2ATP+2H2O
    • L-lactate¬®pyruvate
    • Pyruvate+ NAD++CoA®acetylCoA+CO2+NADH
    • O2 ® anaerobic metabolism ® cell death
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20
Q

What are the cellular effects of ischaemia ?

A

Different tissues have variable O2 requirement and are variably susceptible to ischaemia
Cells with high metabolic rate
Cells with low metabolic rate

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21
Q

What are the clinical effects of ischaemia ?

A

Dysfunction
Pain
Physical damage- specialised cells

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22
Q

What is the outcome of the effects of ischaemia ?

A

No clinical effect
Resolution vs therapeutic intervention
Infacrtion

23
Q

What is infarction ?

A

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

24
Q

What are the possible aetiologies for infarction ?

A

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

25
Q

What does the scale of damage of ischamia/infarction depend on ?

A

Time period
Tissue/organ
Pattern of blood supply
Previous disease

26
Q

What is the mechanism of tissue breakdown caused by infarction ?

A

Anaerobic metabolism - cell death - liberation of enzymes

27
Q

What are the two types of necrosis ?

A

Coagulative necrosis e.g. Heart, lung

Colliquative necrosis e.g. Brain

28
Q

What can coronary arterial obstruction lead to ?

A

Reduced blood flow to region of myocardium, leads to ischaemia, rapid myocardial dysfunction, leads to myocyte death

29
Q

What happens within seconds of myocardial ischaemia ?

A

Anaerobic metabolism, onset of ATP depletion

30
Q

What happens in under two minutes of myocardial ischaemia ?

A

Loss of myocardial contractility (heart failure)

31
Q

What happens within a few minutes of myocardial ischaemia ?

A

Ultrastructural changes (myofibrillar relaxation, glycogen depletion, cell and mitochondrial swelling) ?reversible

32
Q

How long does it take for ischaemia to cause irreversible damage to the heart ?

A

20-30 minutes
Myocyte necrosis (disruption of integrity of sarcolemma membrane leading to the leakage of intracellular macromolecules: blood tests) - Troponin?
Injury to the microvasculature - over 1 hour

33
Q

What do areas of infarction look like less than 24 hours after insult ?

A

No change on visual inspection

A few hours to 12 hours post insult, see swollen mitochondria on Electron Microscopy

34
Q

What do areas of infarction look like within 24-48hrs ?

A

Pale infarct: e.g. myocardium, spleen, kidney, Solid tissues
Red infarct: e.g. in lung, liver, Loose tissues, previously congested tissue; second/continuing blood supply, venous occlusion
Microscopically: acute inflammation initially at edge of infarct; loss of specialised cell features

35
Q

What do areas of infarction look like within 72hrs and onwards ?

A

Macroscopically:
- Pale infarct - yellow/white and red periphery
Red infarct - little change
Microscopically: chronic inflammation; macrophages remove debris; granulation tissue; fibrosis

36
Q

What is the appearance of end result infarcts ?

A

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

37
Q

What is the reparative process of myocardial infarction ?

A 
Cell death
Acute inflammation
Macrophage phagocytosis of dead cells 
Granulation tissue 
Collagen deposition (fibrosis)
Scar formation
38
Q

What happens between 4-12hrs of an MI ?

A

Early coagulation necrosis, oedema, haemorrhage

39
Q

What happens between 12-24hrs of an MI ?

A

Ongoing coagulation necrosis, myocyte changes, early neutrophilic infiltrate

40
Q

What happens between 1-3 days of an MI ?

A

Coagulation necrosis, loss of nuclei and striations, brisk neutrophilic infiltrate

41
Q

What happens between 3-7 days of an MI ?

A

Disintegration of dead myofibrils, dying neutrophils, early phagocytosis

42
Q

What happens between 7-10 days of an MI ?

A

Well developed phagocytosis, granulation tissue at margins

43
Q

What happens between 10-14 days of an MI ?

A

Well established granulation tissue with new blood vessels and collagen deposition

44
Q

What happens between 2-8 weeks of an MI ?

A

Increased collagen deposition, decreased cellularity

45
Q

What happens over 2 months of an MI ?

A

Dense collagenous scar

46
Q

What is a transmural infarction ?

A

Ischaemic necrosis affects full thickness of the myocardium

47
Q

What is a subendocardial infarction ?

A

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

48
Q

What are the histological feature of transmural and subendocardial infarcts ?

A

Histological features are the same (repair time - granulation tissue stage followed by fibrosis - in subendocardial infarct possibly slightly shortened compared to transmural infarct)

49
Q

How are acute infarcts classified ?

A

According to whether there is elevation of the ST segment on the ECG

50
Q

What are the features of a NSTEMI ?

A

No ST segment elevation but a significantly elevated serum troponin level

51
Q

What does a NSTEMI correlate with ?

A

subendocardial infarct

52
Q

What do the effects of infarction depend ?

A

Site
Size of infarct
Death and dysfunction (pain)
Contribution of previous disease and infarction

53
Q

What are the complications of myocardial infarction ?

A

Immediate; early; late
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

Cardiovascular block (28 decks)

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