{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,12]],"date-time":"2026-02-12T10:16:53Z","timestamp":1770891413685,"version":"3.50.1"},"reference-count":8,"publisher":"Oxford University Press (OUP)","issue":"10","license":[{"start":{"date-parts":[[2025,8,29]],"date-time":"2025-08-29T00:00:00Z","timestamp":1756425600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2025,10,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>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 electrocardiogram (ECG)-enabled smartwatches sold worldwide, these devices offer a promising solution for at-home diagnostics and disease tracking.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Methods and results<\/jats:title>\n                  <jats:p>This study examines a 35-year-old male with long COVID, 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-s hand-to-hand single-lead ECG while engaging in 0.1\u2005Hz diaphragmatic controlled breathing, consisting of 5\u2005s of inhalation followed by 5\u2005s of exhalation (Appendix 1). S-\/R-peak amplitude ratios, heart rhythm changes, and other biomarkers were analysed 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. Initially, the patient experienced severe fatigue and heart rhythm changes consistent with POTS. Electrocardiogram 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.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusion<\/jats:title>\n                  <jats:p>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.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1093\/ehjcr\/ytaf425","type":"journal-article","created":{"date-parts":[[2025,8,29]],"date-time":"2025-08-29T15:48:10Z","timestamp":1756482490000},"source":"Crossref","is-referenced-by-count":1,"title":["Monitoring of cardiorespiratory vagal desynchrony using novel biomarkers derived from smartwatch electrocardiograms in a patient recovering from long COVID: case report"],"prefix":"10.1093","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0009-0007-6452-6828","authenticated-orcid":false,"given":"Gustaf","family":"Kranck","sequence":"first","affiliation":[{"name":"Vagus Health Ltd , St. Johns Innovation Centre, Cowley Road, Cambridge CB4 0WS , UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0319-6240","authenticated-orcid":false,"given":"Marcus","family":"St\u00e5hlberg","sequence":"additional","affiliation":[{"name":"Department of Medicine, Karolinska Institutet, Solna, K2 Kardio Pernow J , 17177 Stockholm ,","place":["Sweden"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ulf","family":"Andersson","sequence":"additional","affiliation":[{"name":"Department of Women\u2019s and Children's Health, Karolinska Institutet , KBH, Tomtebodav\u00e4gen 18 A, 17177 Stockholm ,","place":["Sweden"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Johan","family":"Lundin","sequence":"additional","affiliation":[{"name":"Department of Global Public Health, Karolinska Institutet , Tomtebodav\u00e4gen 18 A, 17177 Stockholm ,","place":["Sweden"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Artur","family":"Fedorowski","sequence":"additional","affiliation":[{"name":"Department of Medicine, Karolinska Institutet, Solna, K2 Kardio Pernow J , 17177 Stockholm ,","place":["Sweden"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"286","published-online":{"date-parts":[[2025,8,29]]},"reference":[{"key":"2025100401521395700_ytaf425-B1","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1038\/s41569-023-00962-3","article-title":"Cardiovascular autonomic dysfunction in post-COVID-19 syndrome: a major health-care burden","volume":"21","author":"Fedorowski","year":"2024","journal-title":"Nat Rev Cardiol"},{"key":"2025100401521395700_ytaf425-B2","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1016\/j.biopsycho.2005.11.014","article-title":"Toward understanding respiratory sinus arrhythmia: relations to cardiac vagal tone, evolution, and biobehavioral functions","volume":"74","author":"Grossman","year":"2007","journal-title":"Biol Psychol"},{"key":"2025100401521395700_ytaf425-B3","doi-asserted-by":"crossref","first-page":"354","DOI":"10.1093\/oxfordjournals.eurheartj.a014868","article-title":"Heart rate variability: standards of measurement, physiological interpretation, and clinical use","volume":"17","author":"Malik","year":"1996","journal-title":"Eur Heart J"},{"key":"2025100401521395700_ytaf425-B4","doi-asserted-by":"crossref","first-page":"183","DOI":"10.1111\/j.1469-8986.1993.tb01731.x","article-title":"Respiratory sinus arrhythmia: autonomic origins, physiological mechanisms, and psychophysiological implications","volume":"30","author":"Berntson","year":"1993","journal-title":"Psychophysiology"},{"key":"2025100401521395700_ytaf425-B5","author":"EuroQol Group"},{"key":"2025100401521395700_ytaf425-B6","first-page":"350","article-title":"Significance of a prominent S wave in leads I and V6 in the electrocardiograms of middle-aged and elderly hospital patients","volume":"8","author":"Romo","year":"1976","journal-title":"Ann Clin Res"},{"key":"2025100401521395700_ytaf425-B7","first-page":"149","article-title":"Changes in heart rate and R-wave amplitude with posture","volume":"23","author":"Smith","year":"2003","journal-title":"Clin Physiol Funct Imaging"},{"key":"2025100401521395700_ytaf425-B8","author":"Vanderbilt University Medical Center"}],"container-title":["European Heart Journal - 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