How does fasting prior to 18F-FDG administration affect myocardial metabolism?

Fasting prior to the administration of 18F-FDG, a radiotracer commonly used in PET imaging, has a significant influence on myocardial metabolism. When a patient fasts, the levels of circulating insulin decrease, which promotes a shift in the heart's preferred energy substrate from glucose to fatty acids. This metabolic adaptation allows the myocardium to utilize fatty acids as a primary fuel source during periods of low glucose availability, such as during fasting.

This change in substrate use is particularly important in the context of PET imaging with 18F-FDG, as the radiotracer is a glucose analog; thus, when the heart is primarily utilizing fatty acids, the uptake of 18F-FDG might be reduced. Consequently, fasting can lead to increased effectiveness in diagnosing certain cardiac conditions, as it affects how the heart metabolizes energy during imaging.

Conversely, the other options, while they address aspects related to fasting and metabolism, do not fully capture the primary metabolic shift away from glucose utilization during fasting. Fasting does not necessarily increase insulin sensitivity directly in this context nor does it inherently reduce blood flow to the heart or encourage glucose usage, making the promotion of fatty acid utilization the most pertinent and accurate response regarding the effects of fasting prior to