Pathophysiology of Ischaemia and Infarction Flashcards
What is the definition of ischaemia?
- Supply of oxygen to a tissue/organ is not enough for the demand of the tissue/organ
What are the 4 types of hypoxia?
- Hypoxic
- Anaemic
- Stagnant
- Cytotoxic
What causes hypoxic hypoxia?
- Low inspired O2 level
- Normal inspired O2 but low PaO2
What causes anaemic hypoxia?
- Normal O2 inspiration but blood abnormal
What causes stagnant hypoxia?
Normal inspired O2 but abnormal delivery
- Occlusion of vessels
- Systemic (e.g. shock)
What causes cytotoxic hypoxia?
- Normal inspired O2 but abnormalities at the tissue level
What factors affect oxygen supply?
- Inspired O2
- Pulmonary function
- Blood constituents
- Blood flow
- Integrity of vasculature
- Tissue mechanisms
What factors affect tissue demand?
- Type of tissue
- Activity of tissue above baseline
In ischaemic heart disease what are the supply issues?
- Coronary artery atheroma
- Cardiac failure
- Pulmonary function
- Pulmonary oedema (LVF)
- Anaemia
- Previous MI
What demand issues relate to ischaemic HD?
- Heart has a high demand
- Increases on exercise and stress
What type of atheroma will cause stable angina?
- Established
What type of atheroma will cause unstable angina?
- Complicated
What are the functional effects of ischaemia?
- Blood/O2 supply doesn’t meat demand so demand increases further leading to angina
What is released due to this lack of O2/blood supply?
- Lactic acid from anaerobic respiration
- Ultimately, if not converted back into pyruvate leads to cell death
What are the clinical effects of ischaemia?
- Dysfunction
- Pain
- Physical damage to specialised cells that can’t be replaced
What is the definition of infarction?
- Ischaemic necrosis within a tissue/organ by occlusion of either the arterial supply or venous drainage
What does the scale of damage caused by infarction depend on?
- Time period
- Tissue/organ affected
- Pattern of blood supply
- Previous disease
What is coagulative necrosis and where does it occur in response to infarction?
Dead tissue arrangement is left for a few days following infarction i.e. in the heart
What is colliquitive necrosis and where does it occur in response to infarction ?
Dead tissue is liquefied into a liquid viscous mass i.e. the brain
What order does the myocardium lose it’s ability to function following infarction?
- Anaerobic metabolism (a few seconds after)
- Loss of myocardial contractility (<2 mins)
- Ultrastructural changes (a few minutes)
What are the ultrastructural changes following ischaemia?
- Myofibrillar relaxation
- Glycogen depletion
- Cell and mitochondrial swelling
- All are reversible unless ischaemia is very long
On investigation what can be seen less that 24 hours following an infarct?
- No visual inspection change
- Swollen mitochondria on electron microscopy
What changes can be seen 24-48 hours post infarct?
- Pale infarct
- Red infarct
- Acute inflammation at edges of infarct
What structures does a pale infarct occur?
- Myocardium
- Spleen
- Kidney
- Solid tissue
What structures does a red infarct occur?
- Lung
- Liver
- Loose tissue
What can be seen 72 hours after pale infarct?
- In a pale infarct, yellow white and red periphery
What can be seen 72 hours after red infarct?
Little change
What can be seen microscopically 72 hours after?
- Chronic inflammation
- Macrophages
- Granulation tissue
- Fibrosis
- Neutrophil polymorphs
What is the end result following an infarction (if survival)
- Scar tissue replaces tissue damage
What is the process of scar tissue formation in an MI?
- Cell death
- Acute inflammation
- Macrophages phagocytose dead cells
- Granulation tissue
- Collagen deposition
- Scar formation
Where does ischaemic necrosis extent from and to in a transmural infarction?
The full width of the myocardium
What is a subendocardial infarction?
- Ischaemic necrosis mostly limited to zone of myocardium beneath the endocardial lining
How are acute infarcts classified?
- Elevation of the ST segment on the ECG
What classifies a non STEMI?
- No elevation of the ST segment
- Serum troponin level risen
What do non-STEMI’s correlate with?
- A subendocardial infarct
