24-Hour Heart Rate Variability in Subjects with Postural Orthostatic Tachycardia Syndrome (POTS)

Abstract

Introduction: Postural orthostatic tachycardia syndrome (POTS) is characterised by symptoms of palpitations and lightheadedness on standing from a recumbent position, presyncope or syncope and tachycardia without hypotension during tilt table testing. We hypothesised women with POTS have reduced heart rate variability (HRV), compared to women with neurocardiogenic syncope (NCS) and healthy controls without syncope which can be detected by HRV analysis of 24 h ECGs during daily life. Methods: We examined heart rate (HR) and HRV during 24 h ECG recordings (Philips Zymed) in 37 women (mean age 29 years) including 9 with POTS confirmed by tilt table testing, 8 with NCS thought not to be POTS and 20 healthy women without syncope. Results: Mean maximal 24-hour HR was significantly higher in POTS patients than controls without syncope (168 ± 27bpm vs 147 ± 16bpm, p = 0.03) but was similar to those with NCS (168 ± 27bpm vs159 ± 16bpm; p = 0.62). Mean maximum HR was similar in women with NCS and healthy controls (p = 0.31). POTS patients had lower HRV, demonstrated by reduced RMSSD (square root of mean of squares of successive R-R interval differences), relative to those with NCS (30 ± 17msec, 46 ± 23msec; p = 0.07), and without syncope (30 ± 17msec, 41 ± 15msec; p = 0.03). Conclusion: Mean maximum heart rates were elevated in POTS and NCS compared with controls without either POTS or NCS suggesting that there is some pathophysiological overlap between POTS and NCS. Reduced HRV was typical of POTS and not either NCS or controls, suggesting sympathetic overactivity and relative vagal deficiency. These parameters were detectable by HR and HRV analysis of 24-hour ECG during daily life.