Wearable heart rate variability monitoring identifies autonomic dysfunction and thresholds for post-exertional malaise in Long COVID

Objectives Patients with Long COVID experience disabling fatigue, autonomic dysfunction, reduced exercise capacity, and post-exertional malaise (PEM). Heart rate variability (HRV) can evaluate autonomic function and monitor overexertion, potentially helping to mitigate PEM. This study aimed to use continuous multi-day HRV recordings to monitor overexertion and study autonomic function in Long COVID. Method Heart rate and HRV were continuously measured in 127 patients with long COVID (43±11 years, 32% male) and 21 healthy controls (42±13 years, 48% male), and daily life activities tracked in a logbook. Participants underwent a (sub)maximal cardiopulmonary exercise test to determine heart rate at the first ventilatory threshold (VT1) to study HRV responses to exercise at different intensities. Results HRV was lower in patients with long COVID compared to healthy controls during various daily activities and sleep (p<0.027). HRV remained lower for 24 hours after exercise below, at or above VT1 in patients, but not in healthy controls (p=0.010). Nighttime HRV decreased with intense exercise and longer durations in patients with long COVID (p=0.018), indicative of exercise-induced diurnal disturbances of the autonomic nervous system in long COVID. Conclusion Heart rate variability, assessed by wearables, confirms autonomic dysfunction in patients with long COVID. The delayed recovery of the sympathovagal balance after exercise close and above to VT1 suggests that VT1 can be practically interpreted as a PEM threshold. Application These results confirm the applicability of wearables to assess autonomic function and manage overexertion in long COVID patients. Summary Box What is already known on this topic Patients with long COVID often experience fatigue, autonomic dysfunction, and post-exertional malaise (PEM). HRV can be used as a non-invasive tool to measure autonomic function and recovery. Anecdotal evidence suggests lower HRV in patients with long COVID, but measurements are usually very short. What this study adds This study demonstrates that continuous HRV monitoring through wearables can effectively identify overexertion and autonomic dysfunction during daily activities in patients with long COVID. Patients with long COVID have a lower heart rate variability during sleep and HRV remained significantly lower for a longer period after moderate-to-heavy exercise, that is generally associated with the induction of post-exertional malaise. How this study might affect research, practice, or policy This study supports the use of wearables for assessing autonomic function and overexertion in daily life, helping patients with long COVID in pacing daily activities to mitigate symptoms of post-exertional malaise. HRV tracking after exercise shows that VT1 is a potential threshold for PEM. Sports physicians and physiotherapists can incorporate HRV biofeedback measures into pacing advice to patients. Additional research is needed to further investigate the effect of such an intervention.