Cardiac metabolism imaging

Full text: The use of substrate-specific radiotracers like C-11 palmitate, C-11 acetate, radiolabeled glucose analogs, and O-15 oxygen with PET permits the qualitative, and even more importantly, quantitative assessment of the myocardium's substrate metabolism. Investigations with these radiotracers and PET have succeeded in delineating the normal human heart's substrate metabolism and its responses in substrate selection to changes in plasma substrate and hormone levels as well as to pharmacological stress. Other studies have demonstrated age- and disease- related effects on the myocardium substrate utilization as well as on the efficiency of substrate utilization relative to generation of contractile work. Clinically most relevant has been the application of cardiac metabolism imaging to the assessment of the potential reversibility of contractile dysfunction (also called 'myocardial viability') in patients with ischemic cardiomyopathy. In dysfunctional myocardial regions with diminished blood flow at rest, potential reversibility is reflected by a sustained increase in the regional myocardial extraction of glucose. Myocardial viability as identified by cardiac metabolism imaging is highly predictive of the increased risk of cardiac death and morbidity in patients with ischemic cardiomyopathy on medical treatment. Conversely, such metabolically defined myocardial viability in patients with ischemic cardiomyopathy is predictive of an improvement in long-term survival, in congestive heart failure related symptoms, and in left ventricular function after successful coronary revascularization. (author)