2.4 Cellular Reactions to myocardial ischaemia Flashcards
define myocardial ischaemia
failure of oxygen and substrate delivery to meet myocardial requirements
what is the main factor in early myocardial ischaemia?
discorded calcium handling
what are the electrophysiological and functional consequences of increased Ca?
Electro: early afterdepolarization and delayed afterdepolarization
Functional: relaxation failure, contraction failure and cardiac contracture
what is early after depolarization?
Calcium overload with abnormal phase 2 or 3
phase 2 due to calcium
phase 3 due to sodium
leads to several rapid action potentials
what is delayed after depolarization
increased intracellular Ca which leads to delayed after depolarization in phase 4 - associated with the formation of arrhythmias
what is the progression of the effects of myocardial ischaemia
Calcium overload state - myocardial stunning - myocardial hibernation - cell death
what is myocardial stunning?
short term, mild, sub lethal ischaemia which has persistent contractile depression despite restoration of blood flow and no irreversible damage
Mechanisms of myocardial stunning?
calcium overload and oxygen free radicals
what are the mechanisms of calcium overload?
most plausible is troponin 1 degradation
decreased myofilament response to Ca
what is myocardial hibernation?
prolonged contractile depression which may be protective - cellular integrity maintained and restoration of blood flow improves contractile function
what are the two mechanisms of cell death
necrosis and apoptosis
