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Cardiac metabolic imaging
- 1. Cardiac metabolic imaging Dr.Vishnukumar R, MD Nuclear Medicine Jawaharlal Institute of Post graduate Medical Education and Research (JIPMER), Puducherry, India.
- 2. Learning objectives • Various substrates utilized for cardiac metabolism in different suituations. • Clinical relevance of metabolism • Tracers available • Clinical application.
- 3. Overview of cardiac metabolism
- 4. Glycolysis Pyruvate Acetyl-Co-A Kerbs cycle and ETC (Co2 and H20) Lactate Fatty acid If less or absent O2 O2ispresent Glucose
- 5. S.NO METABOLIC STATE SUBSTRATE USED 1 FASTING FATTY ACIDS 2 FED STATE GLUCOSE 3 EXERCISE FATTY ACID 4 STARVATION KETONE BODIES • Pyruvate, lactate, amino acids are also utilized. • Substrate utilization depends on metabolic state, relative concentration in blood, insulin levels, catecholamine levels and oxygen.
- 6. Clinical relevance • Hibernating tissue- substrate is Glucose (GLUT-4) • Myocardial ischemic memory – Decreased oxidative metabolism – Decreased fatty acid metabolism – Activation of GLUT-1 • Cardiomyopathy and heart failure – Decreased expression of PPAR-α – Decreased fatty acid uptake, oxidation and storage. – Over dependance on glucose metabolism – Early increase in glucose metabolism followed by late decline.
- 7. Tracers available • Carbohydrate metabolism F-18 FDG C-11 Glucose C-11 Lactate • Fatty acid metabolism C-11 Palmitate F-18 FTHA F-18 flurothiapalmitate • Myocardial oxygen consumption O-15 water C-11 acetate
- 8. Clinical applications • Myocardial viability assessment • Hot spot imaging for ischemia • Heart failure
- 9. Myocardial viability • Principle: Resting glucose utilization (GLUT-4) • FDG injected after glucose load (oral or intravenous) • Oral glucose: – Administer 25-50g of glucose orally – Measure BG at 45-60 mins – Administer FDG when BG is between 100 and 140 mg/dl.
- 10. Prime FBG < 140mg/dl- 6U RI FBG > 140mg/dl- 10U RI Mix 100 U regular insulin in 500ml of NS Infuse @ 1.2ml/kg/hr When BG <140 mg/dl start 20D @1.8ml/kg/hr Maintain BG at 80 to 140 mg/dl for 30 minutes Inject FDG and scan after 40-60 mins Maintain infusion for 30-40 mins or till end of the study
- 12. • Findings – Metabolic perfusion mismatch (hibernating myocardium) – Normal perfusion and normal metabolism (normal myocardium, stunned myocardium) – Perfusion and metabolism match (scar) – Reverse mismatch pattern (non ischemic cardiomyopathy, diabetes)
- 14. Hot spot imaging for ischemia • Principle: Myocardial ischemic memory • Patient will be made to fast for 12 hours, then subjected to stress. FDG will be injected at peak stress. • Findings: – Ischemic myocardium preferentially utilizes glucose. – Increased FDG uptake is seen in the areas of ischemia.
- 19. Take home points • Fasting- fatty acids; fed- glucose; exercise- fatty acids • Ischemic myocyte- increased glucose utilization at exercise. • Hibernating myocardium- resting utilization of glucose. • Heart failure- early increase in glucose followed by decline in late stages; decrease in fatty acid metabolism.