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Background Sleep regularity is an emerging key indicator of cardiovascular health. Irregular sleep/wake pattern is strongly associated with heightened risk of major adverse cardiovascular events and cardiometabolic mortality. However, little is known about the effect of poor sleep regularity among older patients with heart failure (HF).Purpose To evaluate sleep regularity among older patients with HF using accelerometer and to examine factors associated with irregular sleep pattern.Methods We recruited 150 patients with HF, aged ≥ 65 from a hospital-based HF clinic between March -October 2023. Patients’ sleep/wake pattern was assessed using a wrist accelerometer, worn for 7 days on the non-dominant hand (24 hours/day). Sleep regularity is quantified in terms of Sleep Regularity Index, SRI (score 0–100; higher scores indicating greater sleep regularity). Concurrent assessments included frailty (Clinical Frailty Score, CFS), HRQoL measure (KCCQ-12) and ADL assessment (Barthel Index). Based on SRI distribution, patients were categorised as highly irregular sleepers (SRI ≤ 36.2; lower tertile), moderately irregular sleepers (SRI 36.3 – 51.1; middle tertile) and regular sleepers (SRI ≥ 51.2; upper tertile).Results Accelerometry data from 145 participants were included in the analysis; median age 80 (range 65–94 years), 36% female. Sixty seven percent were frail (CFS ≥ 5). Median NT-proBNP was 2040 ng/L (IQR = 1117 - 4915), 47% had preserved ejection fraction (HFpEF), 22% had NYHA class III/IV symptoms.The mean SRI of the study population was 43.9 (SD = 17.2). Ninety-six participants (66%) were identified as ‘irregular sleepers’, of which 32% were ‘highly irregular’ sleepers. Irregular sleepers had significantly poorer QoL (KCCQ-12), particularly within the physical and social limitation domains. They also had worse physical functions (Barthel Index) compared to those with regular sleep patterns (table 1).Abstract 5-016 Table 1Baseline characteristics of participants stratified by Sleep Regularity Index (SRI) Demographics Regular sleepers* (SRI ≥ 51.2) N = 49 Moderately irregular sleepers* (SRI 36.3 – 51.1) N = 49 Highly irregular sleepers* (SRI ≤ 36.2) N = 47 P -value Age, year 78 (74–85) 79 (77–85) 82 (74–86) 0.549 Male 33% (N =31) 34% (N =32) 32% (N =30) 0.977 NT-proBNP, ng/L 1945 (1098–5289) 2578 (1304–4535) 1876 (980–5072) 0.841 HF PhenotypeHFrEFHFmrEFHFpEF 35% (N =19)36% (N =8)32% (N=22) 33% (N =18)41% (N =9)32% (N =22) 33% (N =18)23% (N =5)35% (N =24) 0.862 NYHA Class (III/IV) 16% (N=5) 41% (N=13) 44% (N=14) 0.102 Frailty (CFS ≥ 5) 26% (N=25) 37% (N=36) 37% (N=36) 0.287 No. of comorbidities, ≥ 5 17% (N=5) 41% (N=12) 41% (N=12) 0.185 KCCQ-12OverallKCCQ-PLKCCQ-SFKCCQ-QoLKCCQ-SL 62.5 (47.4–76.0)50.0 (41.7–75.0)62.5 (55.2–85.4)62.5 (25.0–75.0)66.7 (41.7–83.3) 47.9 (32.8–75.0)41.7 (25.0–58.3)58.3 (35.4–73.9)50.0 (37.5–75.0)58.3 (33.3–79.2) 51.0 (26.0–63.5)41.7 (16.7–58.3)58.3 (35.4–75.0)50.0 (25.0–75.0)50.0 (25–66.7) 0.0280.0070.1270.3760.008 Barthel Index, % 95 (85–100) 95 (85–100) 85 (70–95) < 0.001 *continuous variables reported as median (IQR), categorical variables reported as N (%)When SRI is considered as continuous variable, lower score had significant association with higher NYHA class (β = -0.009, p = 0.007), worse frailty status (β = -0.017, p < 0.001), poorer QoL (β = 0.344, p = 0.001) and functional ability (ADL) (β = 0.310, p < 0.001), after adjusting for age, gender and number of comorbidities.Conclusion In older patients with HF, poor sleep regularity was significantly associated with worse HF symptom burden, frailty status, QoL and physical performance.