Myocardial perfusion and viability assessment is important for many reasons:
to diagnose, locate and grade the severity of coronary artery disease
to identify candidates who would benefit from revascularization
to evaluate response to revascularization
Terminology
Stunned myocardium
Stunned myocardium refers to a state in which there is wall dysfunction but the perfusion (resting and stress) is normal; (see the main article on stunned myocardium for more details).
Myocardial ischemia
Myocardial ischemia refers to a state in which there is decreased perfusion of the myocardium when stressed (such as during exertion) but normal perfusion during rest (seen as reversible perfusion defect). These patients will significantly benefit from treatment.
Hibernating myocardium
With hibernating myocardium, the myocardium shows decreased perfusion on both stress and resting phase (seen as a fixed defect) but the myocytes are viable and will benefit from revascularization (see hibernating myocardium for more details).
Myocardial infarction
In myocardial infarction, there is absent perfusion both when the heart is stressed and at rest (a fixed defect) and the myocytes are not viable. There will be no benefit from revascularization; (see myocardial infarction for more details).
Imaging techniques
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thallium-201 SPECT
excessive radiation dose (in comparison to Tc-99m MIBI)
redistribution may occur
single injection for stress and resting phase
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technetium-99m MIBI SPECT
less radiation dose
no redistribution
separate injections for stress and resting phase
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FDG-PET (for viability)
based on the fact that myocardium utilizes glucose for metabolism when under effect of ischemia (hence the ischemic myocardium will show greater uptake than normal cells)
under normal circumstances, it utilizes fatty acids for energy
non-viable myocardium will not show any uptake
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no ionizing radiation exposure
dynamic imaging with gadolinium for perfusion
delayed imaging for viability assessment
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CT myocardial perfusion imaging
single phase or dynamic perfusion imaging during stress +/- rest
coronary arteries can be assessed at the same time