§
Transient
& localised reduction of blood supply to the myocardium
§
most
commonly caused by degenerative changes in coronary arteries
§
associated
with atherosclerosis &/or arteriosclerosis [coronary heart disease (CHD)]
§
extent of
myocardial ischaemia is dependent on:
i)
Degree of
occlusion of vascular lumen
ii)
Location
& extent of vascular occlusion (whether proximal of distal; degree of
collateral blood supply)
i)
Metabolic
demand of myocardium (workload ie heart rate, afterload, preload)
ii)
Eg caused
by physical exercise or emotional stress
i) Spastic constriction
- usually early stages of
CHD
- local spasm of a coronary
artery 2°:
a) Nervous reflex: exposure
to wind or cold
b) Local irritation of
smooth muscle adjacent to atherosclerotic plaque eg: nicotine or caffeine
ii) Occlusion
- usually later stages of
CHD
- characteristically
progressive & irreversible
- when plaque breaks
through intima
—> contact with blood
—> initiate thrombus
—> occlude vessel
—> portion of clot breaks
away —> distal vessel embolisation