Myocardial oxygen supply and demand
Balance of myocardial oxygen supply
and demand. Transient ischemic episodes arise from imbalanced
myocardial oxygen supply and demand. Determinants of myocardial
oxygen supply include coronary blood flow, intraluminal coronary
artery size, coronary perfusion pressure, hemoglobin oxygen
content, and duration of diastole. Determinants of myocardial
oxygen demand include heart rate, blood pressure, myocardial
contractility, left ventricular (LV) size, and duration of systole.
Any imbalance between supply and demand may induce ischemia (silent
or symptomatic); however, silent ischemia during daily life tends
to occur at low heart rates and activity levels when compared with
ischemia evoked during exercise testing .
Studies of pathology have shown no definitive coronary morphologic
differences between asymptomatic and symptomatic forms of coronary
heart disease . Therefore, a dynamic coronary
obstructive component in addition to the fixed obstruction may be a
greater contributor to the development of ischemia occurring during
daily life than to that occurring during exercise stress
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