Cardiac neurotransmission imaging.

Cardiac neurotransmission imaging with SPECT and PET allows in vivo assessment of presynaptic reuptake and neurotransmitter storage as well as of regional distribution and activity of postsynaptic receptors. In this way, the biochemical processes that occur during neurotransmission can be investigated in vivo at a micromolar level using radiolabeled neurotransmitters and receptor ligands. SPECT and PET of cardiac neurotransmission characterize myocardial neuronal function in primary cardioneuropathies, in which the heart has no significant structural abnormality, and in secondary cardioneuropathies caused by the metabolic and functional changes that take place in different diseases of the heart. In patients with heart failure, the assessment of sympathetic activity has important prognostic implications and will result in better therapy and outcome. In diabetic patients, scintigraphic techniques allow the detection of autonomic neuropathy in early stages of the disease. In conditions with a risk of sudden death, such as idiopathic ventricular tachycardia and arrhythmogenic right ventricular cardiomyopathy, PET and SPECT reveal altered neuronal function when no other structural abnormality is seen. In patients with ischemic heart disease, heart transplantation, drug-induced cardiotoxicity, and dysautonomias, assessment of neuronal function can help characterize the disease and improve prognostic stratification. Future directions include the development of tracers for new types of receptors, the targeting of second messenger molecules, and the early assessment of cardiac neurotransmission in genetically predisposed subjects for prevention and early treatment of heart failure.