Use and limitations of metabolic tracers labeled with positron-emitting radionuclides in the identification of viable myocardium.

Identification of viable myocardium is crucial in identifying patients who could benefit from interventional therapy such as coronary artery balloon angioplasty or bypass surgery. PET can be used to prospectively identify viable from nonviable myocardium based on the pattern of substrate use in comparison with perfusion. Viable myocardium can be identified with such diverse tracers as 1-11C-palmitate (for assessment of fatty acid metabolism) and 18F-fluorodeoxyglucose (for assessment of the uptake of glucose). Recent studies have suggested that assessment of oxidative metabolism with tracers such as 1-11C-acetate may predict with the greatest accuracy segments of myocardial tissue that will recover after recanalization. Further studies will be necessary to determine whether PET represents a superior technology compared with other more widely available (and less expensive) approaches for identification of jeopardized myocardium. Nonetheless, PET should provide a better understanding of the pathophysiology of myocardial ischemia (since it enables delineation of the biochemical alterations that underlie contractile dysfunction) and of therapeutic strategies likely to be beneficial. It will also be useful for the identification of viable from nonviable myocardium when results of other diagnostic techniques are equivocal, and in patients who are at high risk.