Background Cardiac sympathetic innervation comes from the paravertebral cervical and thoracic ganglia. Among them, the stellate (cervicothoracic) ganglion is a major source of sympathetic innervation. It constantly connects with phrenic nerves and almost as often to the vagal nerves.37 The paravertebral ganglia also directly connect with spinal nerves, which connect with the intercostal nerves. These intercostal nerves split into ramus cutaneous lateralis and a deep branch to the musculus rectus abdominis. Histological studies of human skin biopsy confirmed the presence of abundant sympathetic nerves in arteriovenous anastomoses arrector pilorum muscles, and arterioles. Using horseradish peroxidase as tracer, Baron et al and Taniguchi et al found that all skin sensory and sympathetic neurons are located ipsilaterally. The sympathetic somata are located in the middle cervical and stellate ganglia as well as the thoracic ganglia. Because of the direct and extensive connections among various nerve structures, it is possible for the sympathetic nerves in the various structures to activate simultaneously. Therefore, the investigators hypothesized that SKNA recorded from the upper thorax can be used to estimate the cardiac sympathetic tone.