Lecture 43: Ischemic Dirsorders of the Myocardium Flashcards
What are the two types of ischemia?
- non-lethal
- lethal
Ischemia = inadequate blood flow that leads to inadequate O2 and inadequate removal of waste
Reperfusion can alter these events
What does lethal ischemia lead to?
Coagulative necrosis
What is ischemia caused by?
- reduced blood flow
2. increased myocardial demand
What is the most important cause of ischemic heart disease?
Atherosclerosis
Clinically important atherosclerosis affects epicardial coronary arteries
What is the layer most susceptible to ischemic injury?
Subendocardium because flow is from epicardial to endocardial, and is subjected to most resistance due to shear forces
Whats the collateral circulation like in the coronaries?
They are minimal but can form when there is a coronary occlusion
What are the earliest changes to myocardium in ischemia?
- switch from aerobic to anaerobic metabolism
- cessation of contraction
- altered electrical activity
- relaxation of myofibrils, allowing stretch of myocytes by still contracting adjacent myocardium
Changes are reversible for up to 20-40 minutes
How long can myocardial tissue live without perfusion?
20 minutes
What happens if myocardium ischemic for >40 minutes?
First coagulative necrosis starting with most susceptible layer (subendocardium)
Necrosis followed by phagocytosis (polys then macrophages)
Healing by replacement with granulation tissue progressing to a scar
When you reperfuse myocardium, what modifications may the myocardium undergo?
- stunning
- precondition
- hibernation
- contraction band necrosis
- Reperfusion injury
When there is an occluded artery, what is the first part of myocardium to necrose?
The subendocarium
What are the clinical consequences of MI?
- silent angina
- stable angina pectoris (when pain is felt with increased workload/activity and is relieved with rest)
- Prinzmetal’s (variant) angina
- Cardiac pain occurring during sleep
- caused by vasospasm
- acute coronary syndromes (unstable angina)
What does stenosis of >75% lead to? >90%?
Angina during exercise
Angina during rest
What are the types of acute coronary syndromes?
- unstable (crescendo) angina
- acute MI
- sudden cardiac death
What are the susceptible plaques?
30-60% narrowing Thin fibrous caps Morell ipid Less SMC More inflammation Disruption leads to superimposed thrombus
What does incomplete obstruction by thrombus lead to?
Unstable angina
Subendocardial MI
Sudden death
What does complete obstruction lead to?
Transmural MI
Sudden death
What can happen to non-lethal thrombi?
- becomes organized and incorporated into the plaque
2. lysed either spontaneously or with medical intervention