Cardiac viability

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Distinguishes hibernating myocardium from scar (i.e. candidates for revascularization)

Matched defect on perfusion and viability indicates non-viable myocardium

Mismatched defect (no perfusion, but positive viability) indicates viable myocardium

Reverse mismatched defect (perfusion, but no viability) can be seen with stunning, LBBB or pacer


  • Myocytes prefer fatty acids in a fasting state when glucose and insulin are low
    • This is why a fasting protocol (6-12 hrs) is preferred when evaluating for cardiac sarcoid
  • Glucose Loading
    • 50 mg of oral glucose
    • Measure blood glucose and administer sliding scale insulin after 1 hour
    • High insulin state will make myocytes prefer glucose


Rest-Rest TI 201 with radiotracer activity on delays

Highest first-pass extraction fraction of any commonly used perfusion tracer, extraction efficiency 90%
K analog tha uses ATPase NA-K pump
Undergoes redistribution - as TI clears from myocardium, it's replaced by circulating TI
Cold defects on early images are due to decreased flow
Ischemic myocardium will fill in on delayed imaging
  • Often performed after Stress-Rest demonstrates fixed defect

Stunned Myocardium

  • Reperfused myocardium after occlusion
  • Normal blood flow, but decreased contractility, will regain function in a few weeks

Hibernating Myocardium

  • Chronic myocardial ischemia with reduction of blood flow and contractility
  • Although myocardium is viable
  • Perfusion defect will be mild or moderate, severe fixed defect compatible with infarct