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Nocturnal Heart Rate Variability in Unexplained Syncope and Sleep Apnea-The SINCOSAS Study
María-José Muñoz-Martínez1,2,3, Manuel Casal-Guisande2,4,5, Bernardo Sopeña3,6
1Pulmonary Department, Hospital Universitario Álvaro Cunqueiro, 36312 Vigo, Spain.
Journal of Clinical Medicine
|November 13, 2025
Summary
Obstructive sleep apnea (OSA) and syncope have distinct nocturnal autonomic patterns. Their coexistence reveals deeper autonomic imbalance, suggesting HRV analysis can improve diagnosis.
Area of Science:
- Cardiology
- Neurology
- Sleep Medicine
Background:
- Heart rate variability (HRV) indicates autonomic nervous system (ANS) function.
- Autonomic dysfunction is implicated in unexplained syncope and obstructive sleep apnea (OSA).
- Nocturnal autonomic patterns in these conditions and their overlap are not well understood.
Purpose of the Study:
- To characterize nocturnal autonomic modulation in patients with unexplained syncope, OSA, or both.
- To compare autonomic patterns across these groups and with controls.
Main Methods:
- Multicenter, cross-sectional, comparative study of 304 adults.
- Four groups: controls, OSA only, syncope only, and syncope with OSA.
- Analysis of time- and frequency-domain HRV parameters from overnight respiratory polygraphy.
Main Results:
- OSA showed increased vagal activity (RMSSD) and reduced sympathetic tone (LF power).
- Syncope demonstrated further sympathetic reduction (LF, VLF) with increased RMSSD, indicating blunted reserve.
- Combined OSA and syncope presented mixed autonomic profiles with profound dysautonomia despite milder OSA.
Conclusions:
- OSA and syncope exhibit unique nocturnal autonomic signatures.
- Coexisting conditions result in significant autonomic imbalance.
- Nocturnal HRV analysis may enhance pathophysiological stratification for syncope and OSA.
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