Ischaemia and Infarction Flashcards

1
Q

What is the definition of Infarction?

A

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

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2
Q

What is the definition of Ischaemia?

A

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

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3
Q

What are the four types of hypoxia?

A

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

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4
Q

What are the factors affecting O2 supply?

A
  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
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5
Q

What factors could effect the O2 demand?

A
  1. exertion eg. exercise, stress

2. heart has a high intrinsic demand of oxygen

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6
Q

Is there a clinical correlation between atheroma and ischaemia?

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

complicated atheroma -> thrombosis -> ischaemia/infarction

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7
Q

name six clinical consequences of ischaemia.

A
¥	MI 
¥	TIA – symptoms of a stroke lasting for less than 24 hours
¥	Cerebral infarction
¥	Abdominal aortic aneurysm
¥	Peripheral vascular disease
¥	Cardiac failure
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8
Q

What are the functionally effects of ischaemia?

A

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

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9
Q

What are the general effects of ischaemia?

A

¥ Acute – obvious signs, breathlessness, chest pain

¥ Chronic – insidious signs

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10
Q

What are the biochemical effects of ischaemia?

A
decrease of O2 
more anaerobic respiration 
acid base balance is altered 
pH decreases 
this causes cell death
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11
Q

What are the cellular effects of ischaemia?

A

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

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12
Q

What causes infarction??

A

cessation of blood flow

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13
Q

Name four ways which can stop blood flow.

A
  1. Thrombosis
  2. Embolism
  3. Strangulation e.g. gut twisted
  4. Trauma - cut/ruptured vessel
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14
Q

What does the scale of damage form infarction depend on?

A
  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
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15
Q

State the sequence of events that cause infarction.

A
coronary artery obstruction (atheroma, thrombosis)
decreased blood flow 
ischaemia 
anaerobic respiration (pH decreases) 
increased cell death 
liberation of enzymes 
breakdown of tissue
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16
Q

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

A

Coagulative necrosis e.g. heart, lung

Colliquitive necrosis e.g. brain (more liquid)

17
Q

What is a myocardial infarction?

A

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.

18
Q

State the sequence and time frame of a MI

A
  1. anaerobic respiration (ATP depletion) = seconds

2. loss of myocardial contraction = 1 hour

19
Q

What is the appearance of a MI at:

A
20
Q

Following on from the question before:

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

A
  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
21
Q

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

A

Transmural infarction - effects full thickness of myocardium

Subendocardial infarction - just under endothelium

22
Q

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

A

Subendocardial

23
Q

what are some complications of MI

A
¥	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
24
Q

Does ST elevation correlate with subendocardial or transmural infarct?

A

transmural