Daytime dysfunction and reduced heart rate variability during NREM sleep stage 3 were both independent risk factors for SUDEP, with an inverse relationship identified between RMSSD during NREM stage 3 and both outcomes.
Key Findings
Results
Patients with a first sleep cycle duration of less than 60 minutes had significantly poorer subjective sleep quality than those with a cycle 1 duration of 60 minutes or more.
Subjective sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI).
Patients with cycle 1 duration <60 min had significantly higher PSQI scores (t test, P<.05).
The study enrolled 127 patients with epilepsy undergoing overnight video-EEG monitoring between December 2020 and June 2022.
Cycle 1 duration was defined as the duration of the first sleep cycle of the whole night.
Results
Daytime dysfunction (the 7th domain of the PSQI) was identified as an independent risk factor for SUDEP.
SUDEP risk was measured using the 7-item SUDEP inventory (SUDEP-7).
Daytime dysfunction reflects impaired waking function attributable to sleep disturbance.
The finding was derived from a sample of 127 patients with epilepsy.
The authors recommend that patients with epilepsy exhibiting daytime dysfunction, especially those with generalised tonic-clonic seizures, should be prioritised for SUDEP risk screening.
Results
RMSSD and PNN50 during NREM sleep stage 3 were independent risk factors for SUDEP.
HRV parameters assessed included root mean square of successive differences (RMSSD) and the percentage of NN50 intervals (PNN50).
These HRV parameters were measured specifically during NREM sleep stages 2 and 3.
Both RMSSD and PNN50 during NREM stage 3 were identified as independent risk factors in multivariable analysis.
An inverse relationship between RMSSD during NREM stage 3 and SUDEP risk was identified.
Results
No positive mediation effect of HRV on the relationship between daytime dysfunction and SUDEP risk was observed.
Despite both daytime dysfunction and HRV parameters being independent risk factors for SUDEP, HRV did not mediate the association between daytime dysfunction and SUDEP risk.
An inverse relationship between RMSSD during NREM stage 3 and both daytime dysfunction and SUDEP risk was nonetheless identified.
This suggests that HRV and daytime dysfunction may represent separate, non-mediating pathways to SUDEP risk.
Results
The study identified an inverse relationship between RMSSD during NREM stage 3 and both daytime dysfunction and SUDEP risk outcomes.
Lower RMSSD values during NREM stage 3 were associated with higher SUDEP risk and worse daytime dysfunction.
RMSSD is a time-domain HRV parameter reflecting parasympathetic autonomic tone.
NREM stage 3 is a deep sleep stage during which autonomic regulation is particularly relevant.
The finding suggests that reduced parasympathetic activity during deep sleep may be a marker of elevated SUDEP risk.
Conclusions
The authors recommend further research into additional factors beyond HRV and potential interventions targeting sleep and autonomic function in epilepsy patients.
The study period ran from December 2020 to June 2022.
Seizure-related characteristics were collected alongside sleep and HRV measures.
Generalised tonic-clonic seizures were specifically highlighted as a subgroup warranting priority SUDEP screening when daytime dysfunction is present.
What This Means
This research suggests that two measurable factors — daytime sleepiness or impaired daytime functioning (a symptom of poor sleep quality) and reduced heart rate variability during deep sleep — are each independently associated with a higher risk of sudden unexpected death in epilepsy (SUDEP). The study followed 127 people with epilepsy who had overnight sleep and brain activity monitoring, and used established questionnaires and physiological measurements to assess sleep quality and the nervous system's control of heart rate. People with shorter first sleep cycles (less than 60 minutes) also reported worse overall sleep quality.
Interestingly, while both daytime dysfunction and heart rate variability during deep sleep (NREM stage 3) were linked to SUDEP risk, heart rate variability did not appear to explain or 'mediate' the connection between daytime dysfunction and SUDEP risk — suggesting these may be two separate pathways contributing to risk. Lower heart rate variability during deep sleep, which reflects reduced activity of the calming branch of the nervous system, was inversely related to both worse daytime functioning and higher SUDEP risk.
This research suggests that clinicians caring for people with epilepsy — particularly those who experience generalised tonic-clonic seizures — should pay close attention to reports of daytime dysfunction as a potential signal for elevated SUDEP risk. The findings point toward sleep quality and autonomic nervous system function as potentially important areas for future research into SUDEP prevention, though the authors note that additional factors and possible interventions still need to be explored.
Shao Z, Hu Z, Tang R, Wang X, Peng W. (2026). Daytime dysfunction and SUDEP risk: Exploring the role of sleep and heart rate variability in epilepsy.. Neurologia. https://doi.org/10.1016/j.nrleng.2026.501940