Myocardial metabolic imaging in the acute care setting

Myocardial perfusion scintigraphy: past, present and future

During the last two decades, radionuclide myocardial perfusion scintigraphy (MPS) has become established as the main functional cardiac imaging technique for the assessment of ischaemic heart disease (IHD). Despite a growing number of alternative functional imaging techniques, MPS still remains the most widely used technique, with a wealth of literature supporting its usefulness in assessing IHD and predicting prognosis. The technique itself has evolved, making it more reliable and robust, with additional ventricular functional information that further defines the prognosis in these patients. With the advent of hybrid single photon emission with CT and positron emission tomography with CT cameras together with the development of new camera technology that enables faster images with less radiation and better resolution, MPS will remain an essential part of IHD investigation. There are new promising radiopharmacological developments and applications such as radiolabelled fatty acids and meta-iodobenzylguanidine. These will widen the scope of nuclear medicine imaging to include patients with cardiac failure and acute chest pain presenting to accident and emergency departments. Nuclear medicine cardiac investigations will continue to have an essential role in the diagnosis, stratification and prognosis of patients with cardiac disease, complementing the new developing cardiac modalities such as CT coronary angiography and MRI.

Fatty acid imaging of the heart

Imaging metabolic processes in the human heart yields valuable insights into the mechanisms contributing to myocardial pathology and allows assessment of the efficacy of therapies designed to treat cardiac disease. Recent advances in fatty acid (FA) imaging using positron emission tomography (PET) include the development of a method to assess endogenous triglyceride metabolism and the design of new fluorine-18 labeled tracers. Studies of patients with diabetes have shown that the heart is resistant to insulin-mediated glucose uptake and that metabolism of nonesterified FA is upregulated. Cardiac PET imaging has also recently shown the increase in myocardial FA uptake seen in obese patients can be reversed with weight loss. And a pilot study of patients with chronic kidney disease demonstrated that PET imaging can reveal myocardial metabolic alterations that parallel the decline in estimated glomerular filtration rate. Recent advances in FA imaging using single photon emission computed tomography (SPECT) have been accomplished with the tracer β-methyl-p-[(123)I]-iodophenyl-pentadecanoic acid (BMIPP). Two meta-analyses showed this imaging technique has a diagnostic accuracy for the detection of obstructive coronary artery disease that compares favorably with SPECT myocardial perfusion imaging and that BMIPP imaging yields excellent prognostic data in patients across the spectrum of coronary artery disease. A recent multicenter study of patients presenting with acute coronary syndromes found BMIPP SPECT imaging has greater diagnostic sensitivity than, and enhances the negative predictive value of, clinical assessment alone. Because of their exquisite sensitivity, nuclear imaging techniques facilitate the study of physiologic processes that are the key to our understanding of cardiac metabolism in health and disease.