Since the invention of electrocardiogram (ECG), ECG has been an important part of clinical practice. A primary reason for the popularity of the ECG is that it is non-invasive and can be performed in any patient by placing electrodes on the skin. The present methods of ECG recording focus on detecting electrical signals from the heart. the investigators propose that with high frequency sampling and high pass filtering, the investigators can also record SNA from the skin. The somata of the subcutaneous sympathetic nerves on the skin are located at the ipsilateral cervical and stellate ganglia. Because the left stellate ganglion nerve activity (SGNA) is known to trigger cardiac arrhythmias, including AF, VF and VF, It is possible that skin SNA can also be used for arrhythmia prediction. the investigators tested that hypothesis in our preclinical studies (supported by R01 HL71140) using canine models. The results showed that subcutaneous nerve activity (SCNA) recorded with implanted electrodes can be used to estimate stellate ganglion nerve activity(SGNA) in normal dogs and in a canine model of ventricular arrhythmia and sudden death. the investigators also showed that SCNA is more accurate than heart rate variability in estimating cardiac sympathetic tone in ambulatory dogs with myocardial infarction.Therefore, SKNA and SCNA may be useful in estimating cardiac sympathetic tone. In addition to studying the autonomic mechanisms of cardiac arrhythmia, these new methods may have broad application in studying both cardiac and non-cardiac diseases. For example, sympathetic tone is important in the pathogenesis of heart failure, atherosclerosis, peripheral neuropathies, epilepsy, vasovagal syncope, renal failure, hypertension and many others diseases. Direct SKNA and SCNA recording may provide new approaches to study the mechanisms of these common diseases. SKNA recording may also have immediate clinical applications by assisting in the diagnosis and treatment of hyperhidrosis (sweaty palms), paralysis, stroke, diabetes, and neuromuscular diseases. It may be used to assist biofeedback monitoring performed by neurologists to control neuropsychiatric disorders. Because of these potential clinical and commercial applications, the investigators propose that this research project is significant.