Non-invasive quantitation of cardiac sympathetic innervation using (11)C-HED PET is feasible and gives reliable estimates of cardiac sympathetic innervation in rabbits. Additionally, although both (11)C-HED and (123)I-MIBG are specific for sympathetic neurons, (11)C-HED may be more specific for intravesicular uptake than (123)I-MIBG in some situations, such as that seen in reserpine pretreatment.

Background Syndrome X has been recognized as a disease that is primarily reflected in the cardiac microvasculature. Myocardial metabolism in this condition has been studied, but not in relation to small vessel pathology. Methods and ResultsIn order to examine the relationship between myocardial metabolism and small vessel pathology, 24 consecutive patients with syndrome X (7 men, 17 women; mean age 58 years) were evaluated by the thallium exercise stress test, positron emission tomography using F-18 fluoro-deoxyglucose (FDG), and an endomyocardial biopsy. All patients showed either diffuse or focal increase in the myocardial uptake of FDG, but only 17 patients (71%) showed hypoperfused areas with partial or complete redistribution in the thallium study. Quantification of myocardial FDG uptake revealed that the value in syndrome X patients was 10-fold higher than in controls (p<0.0001). Histopathological examination revealed that in syndrome X there is an extensive increase in smooth muscle cells and thickening of the vascular wall, even in capillary vessels, and the small vessel lumen was markedly narrowed. There was a significant inverse correlation between FDG myocardial uptake and the microvessel luminal area. Conclusions In syndrome X patients, myocardial FDG uptake is increased extensively, which is strongly associated with narrowed myocardial microvasculature. (Circ J 2004; 68: 220 -226)