Pathophysiology Of Ischaemia And Infarction Flashcards
What are the types of hypoxia?
Hypoxia hypoxia- low inspired o2 or normal inspired 02 but low pa02
Anemia - normal inspired 02 but abnormal blood
Stagnant - normal inspired 02 but abnormal delivery i.e. local: occlusion of a blood vessel or systemic: shock
Sytotoxic - normal inspired 02 but abnormal at tissue level
What factors affect oxygen supply?
Inspired 02 Pulmonary function Blood flow Blood constituents Integrity of blood vessel I.e. if something is occluding it Tissue mechanisms
What factors affect oxygen demand?
Tissue itself- different tissues have different requirements
Activity of tissue above baseline value
In ischaemic heart disease, what many affect the supply of 02 to the heart?
Coronary artery atheroma, pulmonary function due to other disease or pulmonary edema from LVH, anaemia, previous MI
State some of the clinical consequences of ischaemia and infarction
MI Transient ischameic attack Cerebral infarction Abdominal aortic aneurysm Peripheral vascular disease Cardiac failure
What are the clinical effects of ischaemia?
Dysfunction
Pain
Physical damage
What is the definition of infraction?
Ischemic necrosis within a tissue/organ of a living body produced by occlusion of either the arterial blood supply or venous drainage
What factors affect the scale of damage of ischemia/infarction?
Time period
Tissue/organ
Pattern of Blood supply (collateral blood supply)
Previous disease
What is the etiology of infarction?
Occlusion of blood flow
What are the 2 different forms of necrosis?
Coagulative I.e. heart, adrenals, kidney
Colliquitive i.e. brain (digestion of dead cells into a viscous liquid mass)
What is the time limit before myocardial ischaemia progresses to severe ischaemia?
20-30 mins at at this stage it is irreversible
How long does it take for myocardial ischemia to cause myocyte necrosis?
20-40 mins
From myocardial ischemia, how long does it take to undergo anaerobic metabolism causing depletion of ATP?
Seconds
What is the appearance 24-48 after infarction?
Pale infarct in kidney, spleen, myocardium
Red infarct in lung, liver, loose tissues
Microscopically loss of specialized cell features & acute inflammation at the edge of infarction
What is the appearance up to 24 hours after infarction?
No change in appearance
But in microscopy there may be swollen mitochondria
What is the appearance 72 hours onwards from infarction?
Pale infarction - pale / yellow with red periphery
Red infarct - little changes
Microscopically- chronic inflammation, macrophages remove debris, fibrosis, granulation tissue
What is the end result of infarction?
A scar replaces the area of tissue damage
The shape depends on the territory of the occluded vessel
May result in repercussion injury
What is repercussion injury?
When blood flow is restored to a previously ischaemic area, this causes tissue damage.
When blood returns you get inflammation and damage from the 02 free radicals
What is the reparative process of a myocardial infarction?
Cell death Acute inflammation Macrophages phagocytosis of dead cells Granulation tissue Collagen deposition, causing fibrosis = fibrous tissue Scar formation
How long does it take for a dense collagenous scar to develop from a myocardial infarction?
> 2 months
What is the name for ischaemic necrosis which affects the full thickness of the myocardium?
Transmural infarction
What is a subendocardial infarction?
Ischemic necrosis which affects the zone of the myocardium under the endocardial lining of the heart
A non-STEMI is usually associated with what type of ischaemic necrosis?
Subendocardial infarction
Describe the time time frame of the injury caused by ischaemia.
Few seconds - anaerobic respiration causing ATP depletion
<2mins -loss of myocardial contractility
Few mins - changes to the ultra structure
20-30 mins - myocyte necrosis
>1 hr - injury to the microvasculature
What is a bad end result from infarction?
Repercussion injury
What follows cell death in the reparative process of infarction?
Acute inflammation
What follows acute inflammation in the reparative process?
Macrophages phagocytosis of dead cells
What follows macrophage phagocytosis in the reparative process?
Granulation tissue
Collagen deposition
How long after an myocardial infarction do you see early neutrophillic infiltrate and then brisk neutrophillic infiltrate?
Early infiltrate 12-24 hrs
Brisk infiltrate 1-3 days
When does disintegration of dead myofibres occur after an infarction?
3-7 days
When do you begin to see granulation tissue? And where does this first appear?
7-10 days
At the margins
What occurs 2-8 weeks after a MI?
Increased collagen deposition
Decreased cellularity
What are some of the complications of a MI?
Sudden death Arrhythmia Angina Heart failure Pulmonary embolism secondary to DVT Ventricular aneurysm Ventricular wall, septum or papillary muscle rupture Papillary muscle dysfunction = necrosis/rupture = mitral regurgitation
If a MI causes infarction to a papillary muscle what can this result in?
Rupture of the papillary muscle = regurgitation
What is the time frame when there is irreversible damage to the myocardium?
20-30 mins
Where would the infarction of an MI occur which would cauze bradyarthymias?
Inferior MI
What is cardiogenic shock characterised by?
Low blood pressure
Low urine output
High mortality
What is a late complication of a myocardial infarction?
Ventricular aneurysm
