Skin Sympathetic Nerve Activity and Cardiac Arrhythmias

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. Utilize the differential frequency contents of ECG and SNA to record neuECG To preserve the signal and eliminate noise, the American Heart Association (AHA) standard recommendation for low pass filtering of the ECG is 150 Hz for adolescents and adults, and 250 Hz for children. Higher frequency signals, although known to be clinically important, are routinely eliminated by this low pass filtering. Because there is no need to record high frequency signals, the conventional ECG and Holter monitoring devices do not have a wide bandwidth and high sampling rate. neuECG recording takes a different approach. the investigators use equipment with wide bandwidth (2K Hz) and high sampling rate (4K/s-10K/s) to record the signals from the skin. The signal is then band passed between 0.5 Hz and 150 Hz to display ECG signal. The same signals are then high passed at \> 150 Hz to reveal nerve activities. Figure 1 illustrates the above concept. It shows Fast Fourier Transform (FFT) analyses of the signals recorded from the skin. High pass filtering at 150 Hz eliminated the ECG signals. The remaining high frequency signals may contain both muscle and nerve activities. McAuley et al reported that the electromyography (EMG) usually has a frequency of \<100 Hz. At most, small amounts of muscle activities could reach 400 Hz. By high pass filtering at 500 Hz, the EMG is eliminated but so are other signals with frequencies \< 500 Hz. The standard high pass setting for microneurography study is 700 Hz. High pass filtering at 500 or 700 Hz increased the specificity but reduced the sensitivity of SKNA recording. The signal to noise ratio is reduced. However, the basic patterns of nerve discharges remain.