Dolphin
Senior Member (Voting Rights)
Journal Article Accepted manuscript
Monitoring of Cardiorespiratory Vagal Desynchrony Using Novel Biomarkers Derived from Smartwatch ECGs in a Patient Recovering from Long COVID – Case Report
Open Access
Gustaf Kranck, MSc Eng , Marcus Ståhlberg, MD, PhD , Ulf Andersson, MD, PhD , Johan Lundin, MD, PhD , Artur Fedorowski, MD, PhD
European Heart Journal - Case Reports, ytaf425, https://doi.org/10.1093/ehjcr/ytaf425 Published: 29 August 2025
Abstract
Background Long COVID and cardiovascular autonomic dysfunction, including Postural Orthostatic Tachycardia Syndrome (POTS), present significant healthcare challenges. Long-term monitoring is challenging due to the evolving nature of symptoms and the limited availability of objective diagnostic tools. With over 200 million ECG-enabled smartwatches sold worldwide, these devices offer a promising solution for at-home diagnostics and disease tracking.
Methods This study examines a 35-year-old male with Long COVID, Postural Orthostatic Tachycardia Syndrome (POTS), and Chronic Fatigue Syndrome (CFS), who recorded 328 ECGs over using a Samsung smartwatch. The protocol required ECG recordings to be taken first in a sitting posture, followed by a standing position, with slow, controlled breathing. For testing, the patient used a Samsung Smartwatch to perform a 30-second hand-to-hand single-lead ECG while engaging in 0.1 Hz diaphragmatic controlled breathing, consisting of 5 seconds of inhalation followed by 5 seconds of exhalation (Appendix 2). S/R peak amplitude ratios, heart rhythm changes, and other biomarkers were analyzed to assess autonomic function.
Fatigue levels were self-reported via the BREATHE FLOW app using a three-grade scale, and health status was tracked monthly with the EQ-5D-5L model.
Results Initially, the patient experienced severe fatigue and heart rhythm changes consistent with POTS. ECG analysis revealed an increased S-wave amplitude and higher S/R ratio in standing posture, along with worsening Respiratory Sinus Arrhythmia (RSA), indicating cardiorespiratory desynchrony. Over time, as symptoms improved, heart rate responses between sitting and standing normalized, and S/R ratio and RSA index followed self-reported fatigue levels, including fluctuations due to post-exercise fatigue.
Conclusion Smartwatch-derived S/R-wave amplitude ratio may serve as an accessible biomarker for tracking disease progression in Long COVID. Given the widespread availability of smartwatches, standardized at-home protocols could improve diagnostics and monitoring for autonomic dysfunction.
Case Report, Long-Covid, Smartwatch, S/R Ratio, Remote Cardiac Monitoring, Novel Biomarker, Postural orthostatic tachycardia syndrome (POTS) Topic: inspirationfatiguebiological markerspostural orthostatic tachycardia syndromesmartwatchespost-acute covid-19 syndrome
Monitoring of Cardiorespiratory Vagal Desynchrony Using Novel Biomarkers Derived from Smartwatch ECGs in a Patient Recovering from Long COVID – Case Report
Open Access
Gustaf Kranck, MSc Eng , Marcus Ståhlberg, MD, PhD , Ulf Andersson, MD, PhD , Johan Lundin, MD, PhD , Artur Fedorowski, MD, PhD
European Heart Journal - Case Reports, ytaf425, https://doi.org/10.1093/ehjcr/ytaf425 Published: 29 August 2025
Abstract
Background Long COVID and cardiovascular autonomic dysfunction, including Postural Orthostatic Tachycardia Syndrome (POTS), present significant healthcare challenges. Long-term monitoring is challenging due to the evolving nature of symptoms and the limited availability of objective diagnostic tools. With over 200 million ECG-enabled smartwatches sold worldwide, these devices offer a promising solution for at-home diagnostics and disease tracking.
Methods This study examines a 35-year-old male with Long COVID, Postural Orthostatic Tachycardia Syndrome (POTS), and Chronic Fatigue Syndrome (CFS), who recorded 328 ECGs over using a Samsung smartwatch. The protocol required ECG recordings to be taken first in a sitting posture, followed by a standing position, with slow, controlled breathing. For testing, the patient used a Samsung Smartwatch to perform a 30-second hand-to-hand single-lead ECG while engaging in 0.1 Hz diaphragmatic controlled breathing, consisting of 5 seconds of inhalation followed by 5 seconds of exhalation (Appendix 2). S/R peak amplitude ratios, heart rhythm changes, and other biomarkers were analyzed to assess autonomic function.
Fatigue levels were self-reported via the BREATHE FLOW app using a three-grade scale, and health status was tracked monthly with the EQ-5D-5L model.
Results Initially, the patient experienced severe fatigue and heart rhythm changes consistent with POTS. ECG analysis revealed an increased S-wave amplitude and higher S/R ratio in standing posture, along with worsening Respiratory Sinus Arrhythmia (RSA), indicating cardiorespiratory desynchrony. Over time, as symptoms improved, heart rate responses between sitting and standing normalized, and S/R ratio and RSA index followed self-reported fatigue levels, including fluctuations due to post-exercise fatigue.
Conclusion Smartwatch-derived S/R-wave amplitude ratio may serve as an accessible biomarker for tracking disease progression in Long COVID. Given the widespread availability of smartwatches, standardized at-home protocols could improve diagnostics and monitoring for autonomic dysfunction.
Case Report, Long-Covid, Smartwatch, S/R Ratio, Remote Cardiac Monitoring, Novel Biomarker, Postural orthostatic tachycardia syndrome (POTS) Topic: inspirationfatiguebiological markerspostural orthostatic tachycardia syndromesmartwatchespost-acute covid-19 syndrome