ABSTRACT
Free fatty acids (FFA), glucose and lactate are the main fuels of the heart. In addition, ketone bodies and amino acids are used in lesser extent. Several factors affect the use of an individual substrate. These include the plasma concentration of the substrate and alternate substrates, myocardial blood flow and oxygen supply, hormone levels and regulatory effects of metabolites arising during degradation of substrates. The quality of the myocardial image depends on the concentration of tracer in both myocardium and blood. Since several factors affect myocardial substrate metabolism, the metabolic imaging should be performed during standardized metabolic conditions. Analogous to the glucose tolerance test, oral glucose loading (50–75 g) is commonly used to stimulate insulin secretion and regional glucose utilization and thus myocardial 2-fluoroglucose (FDG) uptake. It enhances the image quality with more homogeneously distributed FDG uptake than observed during the fasting state. After a glucose load, plasma insulin concentrations rise, this enhances regional glucose utilization.
