Cardiac viability

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

F18 FDG PET

• 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

Thallium

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