The role of the autonomic nervous system in sudden cardiac death

The autonomic nervous system exerts a modulating effect on the risk of sudden cardiac death (SCD) in the setting of ischemic heart disease. The mechanism by which sympathetic tone increases the risk of ventricular arrhythmias is not known, though regional sympathetic denervation at and apical to the site of transmural infarction may result in regional supersensitivity to circulating catecholamines and play a role in ventricular arrhythmogenesis. [(123)I]MIBG scintigraphy enables noninvasive determination of regional cardiac denervation and may be a useful tool for probing the role of sympathetic nervous system in SCD. Increased vagal tone is generally protective against SCD. Newer tests such as baroreflex slope testing and various techniques for determination of heart rate variability, which provide indices of vagal tone, may have greater predictive value and are powerful tools in assessing the role of autonomic nervous system in SCD.