The postural orthostatic stress syndrome in childhood: HRV analysis and the active standing test

Background: Abnormalities in heart rate variability analysis (HRV) have been found in patients with postural orthostatic stress syndrome (POTS), indicating impaired autonomic function. We screened HRV in children in a 5-minute active standing test. Methods: 48 of nearly 500 (9.6%) screened children had a heart rate increase of more than 35 bpm on average in the first 5 minutes active standing test. These data are compared to well-defined indication groups: Healthy controls (N=47), Anorexia Nervosa (N=43), Obesity (N=52) and operated Congenital Heart Disease (N=38). 150 patients have additional 24-hours Holter ECG. Results: We found nearly no differences of supine and 24-hours heart rate and HRV between POTS patients and the healthy controls. However, there is a collapse of the vagus in the standing position indicated by a highly significant decrease of the HRV parameters RMSSD, pNN50, pNN20, High Frequency Power and the increase of the LF to HF ratio. Linear regression analysis show the significant impact of the patients height on the heart rate increase (T=5.9, p<0.0001) and an inverse impact of the body mass index (T= (-)2.33, p=0.021). Conclusion: We uncover the probably most important point of POTS physiology – the collapse of the vagus in the standing position. We identify the high-risk POTS patients – the tall lean teenagers and children with G-protein coupled receptor autoantibodies.