Myocardial Viability
Definitions¶
| State | Perfusion | Function | Potential recovery |
|---|---|---|---|
| Stunned myocardium | Restored | Temporarily reduced | Likely |
| Hibernating myocardium | Chronically reduced | Reduced | Possible after revascularization |
| Scar | Severely reduced | Reduced | Unlikely |
Viability is most relevant when dysfunctional myocardium may recover after restoration of blood flow.
Imaging Modalities¶
| Modality | Marker of viability |
|---|---|
| FDG PET | Preserved glucose metabolism |
| Thallium SPECT | Delayed redistribution or reinjection uptake |
| Tc-99m SPECT | Preserved resting uptake, sometimes enhanced with nitrates |
| Dobutamine echo | Contractile reserve |
| CMR | Limited transmural late gadolinium enhancement |
FDG PET Patterns¶
PET compares resting perfusion with myocardial glucose metabolism.
| Perfusion | FDG uptake | Interpretation |
|---|---|---|
| Normal | Normal | Normal myocardium |
| Reduced | Preserved or increased | Perfusion–metabolism mismatch: viable myocardium |
| Reduced | Reduced | Matched defect: scar |
| Normal | Reduced | Often inadequate metabolic preparation |
Tip
Reduced perfusion with preserved FDG uptake is the classic pattern of hibernating myocardium.
SPECT Viability¶
Thallium-201¶
Initial uptake reflects perfusion and cellular integrity. Delayed redistribution into a resting defect supports viability.
- Rest–redistribution
- Stress–redistribution
- Reinjection protocols
Tc-99m Agents¶
Preserved resting uptake suggests viable myocardium. Nitrate-enhanced imaging may increase tracer delivery to underperfused but viable regions.
Echo and CMR Correlation¶
Dobutamine stress echo¶
Improved contraction during low-dose dobutamine indicates contractile reserve. A biphasic response—improvement at low dose followed by deterioration at higher dose—strongly supports viable but ischemic myocardium.
CMR¶
Likelihood of functional recovery decreases as LGE becomes more transmural:
- <25% transmural LGE: recovery likely
- 25%–50%: intermediate
-
50%: recovery unlikely
When to Order Viability Testing¶
Consider testing when:
- LV dysfunction is severe
- Dysfunctional territory may be revascularizable
- The benefit of revascularization is uncertain
- The result will change management
Do not order viability imaging when the patient is not a revascularization candidate or the result will not affect treatment.
Evidence and Limitations¶
Viability predicts the potential for regional functional recovery, but it should not independently determine revascularization.
- The STICH viability substudy did not demonstrate that viability identified patients with a differential survival benefit from CABG.
- REVIVED-BCIS2 found that PCI did not reduce death or heart-failure hospitalization in patients with severe ischemic LV dysfunction despite demonstrable viability.
Clinical decisions should integrate coronary anatomy, symptoms, LV remodeling, procedural risk, ischemic burden, and likelihood of complete revascularization.
Board Pearls¶
- Perfusion–metabolism mismatch = viable, hibernating myocardium.
- Matched reduction in perfusion and FDG uptake = scar.
- Biphasic dobutamine response = viable and ischemic.
- Transmural LGE >50% predicts poor functional recovery.
- Viability does not automatically mean revascularization improves survival.