MedicoNotebook: Myocardial perfusion and viability

Author: Dr Ayush Goel

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 re-vascularization
to evaluate response of re-vascularization

Terminology

Stunned myocardium

It refers to a state in which there is wall dysfunction but the perfusion (resting and stress) is normal.

Myocardial ischemia

It refers to a state in which there is decreased perfusion on stress but normal during rest (seen as reversible perfusion defect). These patients will significantly benefit with treatment.

Hibernating myocardium

In this the myocardium shows decreased perfusion on both stress and resting phase (seen as fixed defect) but the myocytes are viable and will benefit from revascularization.

Myocardial infarct

In this there is absent perfusion on both stress and resting phase (seen as fixed defect) and the myocytes are not viable. There will be no benefit from revascularization.

Imaging techniques

thallium-201 SPECT
- excessive radiation dose (c.f. 99mTc-MIBI)
- redistribution may occur
- single injection for stress and resting phase
99mTc-Sestamibi SPECT
- less radiation dose
- no redistribution
- separate injections for stress and resting phase
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
Cardiac MR perfusion imaging