Heart rate variability in patients presenting with neurally mediated syncope in an emergency department

Abstract Background Neurally mediated syncope (NMS) is a disorder of autonomic nervous system (ANS) regulation. Orthostatic stress is one of the most common causative factors seen in clinical practice. Analysis of heart rate variability (HRV) is a non-invasive method that is used to assess ANS regulation. In this study, we investigated the pathophysiology of NMS using HRV in our emergency department. Methods The subjects were 19 patients (age 25.8 ± 6.2 years old) who presented with NMS and 20 healthy individuals (age 26.6 ± 2.7 years old) who served as controls. HRV was measured in supine, sitting and standing positions. Heart rate (HR), low frequency (LF 0.04–0.15 Hz), high frequency (HF > 0.15 Hz), and coefficient of variation of the R-R interval (CVRR) were determined. Results LF and HF in the supine position were significantly lower in the patients with NMS ( p p p p  = 0.0017). Area under the curve was calculated to be 0.824, and at the cutoff value of 4.997 of CVRR in supine, the sensitivity and the specificity were 78.9% and 85.0%. Conclusion The sympathetic and parasympathetic nervous systems were both suppressed in patients with NMS. In post-syncope, parasympathetic withdrawal, rather than sympathetic reactivation, was responsible for the increased HR after syncope. CVRR may serve as a new clinical biomarker in the emergency department.