Pathophysiology of Ischaemia & Infarction Flashcards
What is ischaemia?
Restriction in the blood supply to tissues, causing a shortage of oxygen that is needed for cellular respiration (to keep the tissue alive)
What is a restriction of blood supply to a tissue called?
Ischaemia
What is hypoxia?
Condition where part of the body is not recieving enough oxygen
What is the condition where part of the body is not recieving enough oxygen?
Hypoxia
What are some different kinds of hypoxia?
Hypoxic
Anaemic
Stagnant
Cytotoxic
What is hypoxic hypoxia?
Low inspired oxygen levels or normal inspired oxygen levels but low PaO2
What kind of hypoxia is low inspired oxygen levels or normal inspired oxygen levels but low PaO2?
Hypoxic
What is anaemic hypoxia?
Normal inspired oxygen but blood is abnormal
What is the hypoxia with normal inspired oxygen levels but blood is abnormal?
Anaemia
What is stagnant hypoxia?
Normal inspired oxygen but abnormal delivery, due to local (occlusion of the vessel) or systemic problems (shock)
What is the hypoxia due to normal inspired oxygen but abnormal delivery, due to local (occlusion of the vessel) or systemic problems (shock)?
Stagnant hypoxia
What is cytotoxic hypoxia?
Normal inspired oxygen but abnormal at tissue level
What hypoxia is due to normal inspired oxygen but abnormal at tissue level?
Cytotoxic hypoxia
What are some factors that affect oxygen supply?
Inspired oxygen
Pulmonary function
Blood constituents
Blood flow
Integrity of vasculature
Tissue mechanisms
What are factors that affect oxygen demand?
Tissues itself (different tissues have different requirements)
Activity of the tissue above baseline value
What are the 2 general things that ischaemic heart tissue can be due to?
Supply issues
Demand issues
What are some examples of supply issues that can cause ischaemic heart disease?
Coronary artery atheroma
Cardiac failure (flow)
Pulmonary function (other disease or pulmonary oedema)
Anaemia
Previous myocardial infarction
What is an example of a demand issue that can cause myocardial ischaemia?
Heart has high intrinsic demand, possible due to exertion or stress
What is atheroma/atherosclerosis?
Localised accumulation of lipid and fibrous tissue in intima of arteries
What is localised accumulation of lipid and fibrous tissue in intima of arteries called?
Atheroma/atherosclerosis
What are some of the clinical impacts of atheroma?
Stable angina
Unstable angina
Ischaemia/infarction by thrombosis
Aneurysm (atheroma in the aorta)
What is stable angina?
Established atheroma in coronary arteries
What does an established atheroma in the coronary arteries cause?
Stable angina
What is unstable angina?
Complicated atheroma in the coronary arteries
What is a complicated atheroma in the coronary arteries called?
Unstable angina
What are some possible clinical consequences due to atheroma?
Myocardial infarction
Transient ischaemic attack (TIA)
Cerebral infarction
Abdominal aortic aneurysm
Peripheral vascular disease
Cardiac failure
What does TIA stand for?
Transient ischaemic attack
What is a transient ischaemic attack?
Brief interruption of blood flow to part of the brain that causes temporary stroke like symptoms
What is peripheral vascular disease?
Blood circulation disorder that causes the blood vessels outisde of your art and brain to narrow, block or spasm (happens in arteries or veins)
What is a brief interruption of blood flow to part of the brain that causes temporary stroke like symptoms called?
Transient ischaemic attack
What is a cerebral infarction?
Area of necrotic tissue in th ebrain resulting from a blockage or narrowing in the arteries supplying it with blood
What is an area of necrotic tissue in th ebrain resulting from a blockage or narrowing in the arteries supplying it with blood called?
Cerebral infarction
What is an abdominal aortic aneursm?
Localised enlargement of the abdominal aorta so the diameter is greater than 3cm
What is localised enlargement of the abdominal aorta so the diameter is greater than 3cm called?
Abdominal aortic aneurysm
What is it called when the heart does not pump blood as well as it should?
Heart failure
What is blood circulation disorder that causes the blood vessels outisde of your art and brain to narrow, block or spasm (happens in arteries or veins) called?
Peripheral vascular disease
What is cardiac failure?
Heart does not pump blood as well as it should
What does coronary artery disease lead to, and then what does this lead to?
Coronary artery disease -> myocardial infarction -> cardiac failure
In terms of formular, why does an atheroma have an impact on blood flow?
Atheroma decreases the radius of the vessel, causing decrease in flow (to the power of 4)
This decreases the delivery of oxygen and causes myocardial infarction
What are the different categories of ischaemia?
Acute
Chronic
Acute-on-chronic
How does ischaemia effect cells biochemically?
Decreased oxygen means aerobic respiration is not possible
So cell performs anaerobic respiration
Which does not produce enough energy
Cell death occurs
What can be said about the impact of ischaemia on different tissues?
Different tissues have variable oxygen demands and so have variable susceptibility to ischaemia
What cannot be performed in a cell without oxygen?
Aerobic respiration
What are the clinical effects of ischaemia?
Dysfunction
Pain
Physical damage
What are the possible outcomes of ischaemia?
No clinical effect
Resolution verses therapeutic intervention
Infarction
What is infarction?
Obstruction of the blood supply to an organ or region of tissue causing death of the tissue
What is infarction due to?
Cessation of blood flow
What is the aetiology of infarction?
Thrombosis
Embolism
Strangulation
Trauma
What does the scale of damage due to ischaemia/infarction depend on?
Time period
Tissue/organ
Pattern of blood supply
Previous disease
What is the biochemical process of infarction?
1) Anaerobic respiration
2) Cell death
3) Liberation of enzymes
4) Breakdown of tissue
What are examples of infarction?
Coagulative necrosis
Colliquative necrosis
What is coagulative necrosis?
Accidental cell death typically caused by ischaemia or infarction, architecture of dead tissue is preserved for a few days so if surrounded by healthy tissue regeneration can occur
What is accidental cell death typically caused by ischaemia or infarction, architecture of dead tissue is preserved for a few days so if surrounded by healthy tissue regeneration can occur called?
Coagulative necrosis
What is colliquative necrosis?
Type of necrosis that results in transformation of the tissue into liquid viscous mass
What is the type of necrosis that results in transformation of the tissue into liquid viscous mass called?
Colliquative necrosis
Where does coagulative necrosis occur?
Heart and lungs
Where does colliquative necrosis occur?
Brain
What is the process of myocardial infarction?
1) Coronary artery obstruction
2) Decrease in blood flow to region of the myocardium
3) Ischaemia and rapid myocardial dysfunction
4) Myocyte death
What does myocardial infarction lead to?
Anaerobic respiration, onset of ATP depletion (within seconds)
Loss of myocardial contractility which leads to heart failure (within 2 minutes)
Ultrastructural changes (after a few minutes)
Myocyte necrosis (20-40 minutes)
Injury to the microvasculature (after 1 hour)
What are examples of microstructure changes that occurs due to myocardial infarction?
Myofibrillar relaxation
Glycogen depletion
Cell and mitochrondrial swelling
How does the appearance of infarcts change within less than 24 hours?
No change on visual inspection
A few hours to 12 hours post insult see swollen mitochondria on electron microscopy
How does the appearance of infarcts change between 24-48 hours?
PALE INFARCT
Solid tissues
RED INFARCT
Loose tissues
Previously congested tissues
Second/continuing blood supply
Venous occlusion
MICROSCOPICALLY
Acute inflammation initially at edge of infarct, leading to loss of specialisd cell features
How does the appearance of infacts change after 72 hours?
MACROSCOPICALLY
Pale infarct (yellow/white and red periphery) Red infarct (little change)
MICROSCOPICALLY
Chronic inflammation
Macrophages remove debris
Granulation tissue
Fibrosis
What are examples of pale infarcts?
Myocardium
Spleen
Kidney
What are examples of red infarcts?
Lung
Liver
What is the end appearance of infarction?
Scar replaces area of tissue damage
Shape depend on territory of occluded vessel
Possibly reperfusion
What is reperfusion?
Tissue damage caused when blood supply returns to a tissue after a period of ischaemia
What is tissue damage caused when blood supply returns to a tissue after a period of ischaemia called?
Reperfusion
What is the reparative process after infarction?
1) Cell death
2) Acute inflammation
3) Macrophages phagocytosis of dead cells
4) Granulation tissue
5) Collagen deposition (fibrosis)
6) Scar formation
What is the microscopic process of myocardial infarction?
4 TO 12 HOURS
Early coagulation necrosis
Oedema
Haemorrhage
12 TO 24 HOURS
Ongoing coagulation necrosis
Myocyte changes
Early neutrophilic infiltrate
1 TO 3 DAYS
Coagulation necrosis
Loss of nuclei and striations
Brisk neutrophilic infiltrate
3 TO 7 DAYS
Disintegration of dead myofibrils
Dying neutrophils
Early phagocytosis
7 TO 10 DAYS
Well developed phagocytosis
Granulation tissue at margins
10 TO 14 DAYS
Well established granulation tissue with new blood vessels and collagen deposition
2 TO 8 WEEKS
Increased collagen deposition
Decreased cellularity
MORE THAN 2 MONTHS
Dense collagenous scar
What are the 2 different kinds of myocardial infarction?
Transmural infarction
Subendocardial infarction
What is a transmural infarction?
Ischaemic necrosis affects full thickness of the myocardium
What is it called when ischaemic necrosis affects full thickness of the myocardium?
Transmural infarction
What is subendocardial infarction?
Ischaemic necrosis mostly limited to a zone of the myocardium under the endocardial lining of the heart
What is it called when ischaemic necrosis mostly limited to a zone of the myocardium under the endocardial lining of the heart?
Subendocardial infarction
How do the histological features compare between transmural and subendocardial infactions?
They are the same (same repair time and granulation tissue stage followed by fibrosis)
Clinically, what are acute infarcts classifed according to?
Whethere there is an elevation of the ST segment on the ECG:
NSTEMI
STEMI
Clinically, what are the 2 kinds of acute infarcts?
STEMI
NSTEMI
What does STEMI stand for?
ST elevated myocardial infarction
What does NSTEMI stand for?
Non-ST elevated myocardial infarction
What kind of myocardial infarction is NSTEMI thought to correlate with?
Subendocardial infarction
What does the effects of infarction depend on?
Site of infarct (within body and organ)
Size of infarct
Contribution of previous disease/infarction
What are some possible effects of infarction?
Death
Dysfunciton (pain)
What can complications of myocardial infarction be classified as?
Immediate
Early
Late
What are some examples of complications of myocardial infarctions?
Sudden death
Arrhythmias
Angina
Cardiac failure
Cardiac rupture (ventricular wall, septum or papillary muscle
Reinfarction
Pericarditis
Pulmonayr embolism secondary to deep vein thrombosis
Mitral incompetence
Ventricular aneurysm