Do patients with neurally mediated syncope have augmented vagal tone

Abstract Head-up tilt testing is now recognized as a valuable diagnostic tool for identifying patients with neurally mediated syncope. However, the causes of individual susceptibility to such orthostatic stress have not been well characterized in this patient population. At the time of syncope, there is evidence to suggest both withdrawal of sympathetic tone as well as increased vagal activity. The latter is manifest by bradycardia, increased high-frequency spectral power of heart rate variability and release of pancreatic polypeptide. 1,2 The purpose of this study was to assess the importance of resting autonomic tone assessed by temporal and spectral measures of heart rate variability and vagal reserve assessed by baroreceptor sensitivity in patients with neurally mediated syncope and in control subjects.