Heart rate fragmentation in psychiatry: across age stages and association with conventional heart rate variability

BACKGROUND Heart rate fragmentation (HRF) reflects disorganized beat-to-beat rhythm dynamics not captured by conventional heart rate variability (HRV). This study characterized age-related HRF patterns in psychiatric patients using the percentage of inflection points (PIP) as the primary index and examined differences by sex and diagnosis, as well as associations with conventional HRV. METHODS We included 3,813 patients with schizophrenia, depressive disorder, anxiety disorder, or sleep disorder across four age groups. Three-minute resting electrocardiograms were used to derive PIP, the percentage of alternating segments (PAS), and the conventional HRV indices RMSSD, SDNN, LF, and HF. Group differences were tested by analysis of covariance. Associations between PIP and HRV were assessed using partial Spearman correlations and multivariable linear regression with covariate adjustment. RESULTS PIP increased across age groups, whereas conventional HRV indices declined (all p < 0.001). Males showed higher PIP than females in adolescence and early adulthood, but not in later adulthood. Diagnosis had a significant main effect on PIP, although between-diagnosis differences were modest, and no diagnosis-by-age interaction was observed. PIP was inversely associated with all HRV indices, most strongly with LnHF (all p < 0.001). PAS showed a similar pattern. CONCLUSIONS HRF was higher in older age groups in this psychiatric sample, showed sex differences that varied across age groups, and displayed limited diagnostic specificity. Its robust inverse association with conventional HRV, particularly HF, suggests partial overlap with traditional HRV and supports fragmentation as a complementary marker of beat-to-beat rhythm organization.