Ischemia and Infarction - Physiology Flashcards
Define ischemia
Lack of blood supply to tissue/organ = hypoxia
What are the 4 different types of blood/O2 abnormal perfusion
Hypoxic = low inspired O2. Can also have norm O2 but low paO2
Anaemic = Norm inspired O2 but blood abnormal
Stagnant = Norm inspired O2 but abnormal delivery either: a) Local eg Occlusion or 2) Systemic eg: shock
Cytotoxic = Norm inspired O2 but abnormal at tissue level
What are some blood supply issues?
Coronary artery atheroma Cardiac failure Anaemia Pulm function Previous MI
Does the heart have a high or low intrinsic demand?
High
What are the different types of atherosclerosis?
Established atheroma in coronary a = stable angina
Complicated atheroma in coronary a = unstable angina
Ulcerated/fissured plaque -> thrombosis -> ischaemia/infarction
Atheroma in aorta -> aneurysm
What are some consequences of ischaemia
MI TIA PVD Cerebral infarction Aortic aneurysm Cardiac failure
What are the effects of ischaemia functionally?
Blood/O2 feels to meet demand due to decreased supply or increased demand or both
What are the effects of ischaemia biochemically?
Anaerobic metabolism causes increase lactic acid so leads to cell death
Define what infarction is?
Ischemic necrosis due to occlusion of either arterial or venous vessels
What can result in caessation of blood flow for infarction?
Thrombosis
Embolism
Trauma - cut or ruptured vessel
Enstrangulation eg; gut
Which factors can determine the damage scale for infarction?
Time peroid
Pattern of blood supply
Tissue/organ
Previous disease
What are the 2 types of necrosis?
Coagulative necrosis eg: heart, lung
Colliquitive necrosis eg: brain
Just to note; anaerobic metabolism -> cell death -> liberation of enzymes -> breakdown of tissue
Coronary arterial obstruction -> decrease blood flow to region of myocardium -> ischaemia, rapid myocardial dysfunction -> myocyte death
What are the different myocardial ischemia onset times?
Anaerobic metabolism onset of atop depletion = seconds
Loss of myocardial contractility (-> heart failure) = <2min
Ultrastructural changes = few min
*Severe ischemia = 20-30min = irreversible damage
Myocyte necrosis ( leakage of macromolecules ) = 20-40mins
Injury to microvascular = >1 hour
Describe the appearance of an infarct less than 24hour?
No change on visual inspection
Few-12hours = swollen mitochondria
Describe the appearance of an infarct between 24-48h
Pale infarct and solid tissue: eg myocardium, spleen and kidney
Red infarct and loose tissue ( previously congested tissue, venous occlusion ) eg: lung and liver
Microscopically = acute inflammation initially at edge of infarct ~ loss of specialised cell features
What is the infarct appearance after 72hours?
Macroscopic:
- Pale infarct: yellow/white and red periphery
- Red infarct: little change
Microscopic:
- Chronic inflam
- Macroscopic remove debris
- Granulation tissue
- Fibrosis
What is the appearance of an infarct at the end/end result?
Scar replaces area of tissue damage
Shape depends on territory of occluded vessel
Reperfusion Injury
What is the infarct factors onset for between 4-12hours?
Early coagulation necrosis
Oedema
Hemorrhage
What is the infarct factors onset for between 12-24h?
Ongoing coagulation necrosis
Myocyte changes
Early neutrophillic infiltrate
What is the infarct factors onset for between 1-3days?
Coagulation necrosis
Loss of nuclei + striations
Brisk neutrophilic infiltrate
What is the infarct factors onset for between 3-7days?
Disintegration of dead myofibres
Dying neutrophils
Early phagocytosis
What is the infarct factors onset for between 7-10days?
Well developed phagocytosis
Granulation tissue at margins
What is the infarct factors onset for between 10-14 days?
Well established granulation tissue with new blood vessels and collagen deposition
What is the infarct factors onset for between 2-8weeks?
Increased collagen deposition
Decreased cellularity
What is the infarct factors onset for between >2 months?
Dense collagenous scar
What are the two types of infarcts?
Transmural: ischaemic necrosis affects full thickness of myocardium
Subendocardial:
Ischemic necrosis limited to zone of myocardium under endocardial lining
Which infarct classification can NSTEMI correlate with?
Subendocardial
What are complications associated with infarction?
DARTH VADER Death Arrhythmias Rupture Tamponade Heart failure
Valve disease Aneurysm Dresslers syndrome thromboEmbolism Regurg
