Scintigraphic evaluation of cardiac autonomic innervation

Alterations in cardiac autonomic neuronal function have become the focus of intense research in various cardiovascular diseases. Both single-photon emission tomography (SPECT) and the positron emission tomography (PET) imaging techniques in combination with radio-labeled neurotransmitters and receptor ligands have become available for the scintigraphic visualization of presynaptic and postsynaptic neuronal function. Several clinical studies have shown changes in tracer distribution in different clinical conditions, such as ischemic heart disease, congestive heart failure, malignant arrhythmias, heart transplantation, and in patients with diabetes. In patients with congestive heart failure, previous in vitro investigations have concentrated on the postsynaptic level of the sympathetic innervation. However, alterations in presynaptic nerve function have been demonstrated with scintigraphic investigations by decreased presynaptic tracer retention. Moreover, correlation between scintigraphic findings and clinical outcome was shown in patients with heart failure, providing important prognostic information superior to conventional risk assessment. In conclusion, scintigraphic evaluation by SPECT and PET allows functional characterization of cardiac presynaptic and postsynaptic neurons. Regional tracer uptake can be used as an index for the integrity of innervation in various diseases. Newer tracer approaches may allow the noninvasive quantification of neuronal function by PET.