Heart rate variability across depressive presentations with and without suicidal ideation in university and clinical samples

Abstract Background Reduced heart rate variability (HRV) has been associated with depressive symptoms, clinically diagnosed depression, and suicidal ideation. However, it remains unclear whether similar HRV patterns are observed across distinct university and clinical study contexts. This study examined HRV differences among healthy controls (HC), participants with depressive symptoms or clinically diagnosed depression classified according to study-specific operational criteria as D, and participants classified as DSI according to study-specific criteria. In Study 1, the D group was defined by SSI scores below the prespecified threshold rather than complete absence of suicidal thoughts. Methods A two-study design was used. Study 1 included 86 university students, and Study 2 included 150 clinical participants. Resting-state HRV was recorded during a 5-minute ECG session. The primary outcomes were ln-transformed standard deviation of normal-to-normal intervals (lnSDNN) and root mean square of successive differences (lnRMSSD). Age- and gender-adjusted general linear models were used to test omnibus group effects, linear trends, and planned contrasts. Cross-study analyses were conducted using pooled models based on within-sample standardized lnSDNN and lnRMSSD. Results In the university sample, lnSDNN showed a significant omnibus group effect, and both lnSDNN and lnRMSSD showed significant linear trends, although planned adjacent-group contrasts were not significant after correction. In the clinical sample, both primary HRV indices showed significant omnibus effects, linear trends, and planned contrasts. Additional analyses adjusting for depressive symptom severity after exclusion of the HAMD suicide item showed that DSI remained associated with lower lnSDNN in both samples and with lower lnRMSSD in the clinical sample. Exploratory cross-study analyses showed significant group-related patterns and group × sample interactions, which were interpreted cautiously given the substantial differences between the two samples. Conclusions Lower HRV was associated with depressive symptom burden and suicidal ideation within both the university and clinical samples. The findings were statistically more robust in the clinical study, but differences between studies should be interpreted cautiously because the samples differed substantially in recruitment, clinical characterization, symptom range, and assessment context. Clinical trial number Not applicable.