E3 PreliminaryPreliminaryPEM unclearPeer-reviewedMachine draft
Monitoring of cardiorespiratory vagal desynchrony using novel biomarkers derived from smartwatch electrocardiograms in a patient recovering from long COVID: case report.
Kranck, Gustaf, Ståhlberg, Marcus, Andersson, Ulf et al. · European heart journal. Case reports · 2025 · DOI
Quick Summary
Researchers tracked one long COVID patient over time using a smartwatch to record heart activity while he was sitting and standing. They noticed that when his fatigue improved, his heart's electrical patterns also normalized, suggesting smartwatch recordings could help monitor autonomic dysfunction (when the nervous system struggles to control heart rate and blood pressure). This simple at-home method may offer a practical way for patients to track their own recovery.
Why It Matters
ME/CFS and long COVID patients often lack objective tools to track their fluctuating autonomic symptoms at home. This study demonstrates that widely available smartwatches may provide accessible, real-time biomarkers of heart-breath synchrony that correlate with fatigue and recovery, potentially enabling better self-monitoring and earlier detection of autonomic deterioration without requiring clinic visits.
Observed Findings
- S-wave amplitude increased and S/R ratio elevated in standing posture during initial severe fatigue phase
- Respiratoryrsinus arrhythmia (RSA) worsened initially, indicating cardiorespiratory desynchrony
- Heart rate responses between sitting and standing normalized as self-reported fatigue improved over time
- S/R ratio and RSA index fluctuations tracked with self-reported fatigue levels, including post-exercise malaise episodes
- Patient improved symptomatically and physiologically over the monitoring period
Inferred Conclusions
- Smartwatch-derived S-/R-wave amplitude ratio may serve as an accessible biomarker for tracking autonomic dysfunction in long COVID and ME/CFS
- Cardiorespiratory synchrony metrics obtained from smartwatch ECGs correlate with subjective fatigue and may reflect disease progression
- Standardized at-home smartwatch protocols could improve diagnostics and disease monitoring for autonomic dysfunction in these conditions
Remaining Questions
- Do these smartwatch biomarkers distinguish ME/CFS from other autonomic conditions (POTS alone, dysautonomia, anxiety disorders)?
- What is the test-retest reliability and validity of smartwatch-derived S/R ratios compared to standard clinical ECG or autonomic testing?
What This Study Does Not Prove
This case report does not prove that S/R ratios cause fatigue or that smartwatch biomarkers are diagnostic for ME/CFS; it only shows correlation in one patient. The study cannot establish whether these metrics are specific to autonomic dysfunction in ME/CFS versus other conditions, and lacks controls to validate the biomarkers against gold-standard autonomic testing. Generalizability to other patients remains entirely unknown.
Tags
Symptom:Post-Exertional MalaiseOrthostatic IntoleranceFatigue
Biomarker:Blood Biomarker
Phenotype:Long COVID Overlap
Method Flag:PEM Not DefinedNo ControlsSmall SampleExploratory Only
Metadata
- DOI
- 10.1093/ehjcr/ytaf425
- PMID
- 41050528
- Review status
- Machine draft
- Evidence level
- Early hypothesis, preprint, editorial, or weak support
- Last updated
- 8 April 2026
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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