ObjectiveThe monocyte-to-high-density lipoprotein cholesterol ratio (MHR) integrates inflammatory burden with anti-inflammatory lipid status, yet its prognostic value for long-term outcomes in critically ill patients with coronary heart disease (CHD) remains unclear. This study aimed to evaluate the association between MHR and 1-year all-cause mortality in this high-risk population.MethodsWe conducted a retrospective cohort study using data from the Medical Information Mart for Intensive Care (MIMIC)-III and IV databases (2001-2019). Adult patients (≥18 years) with CHD were included, excluding those with ICU stay <24 hours or missing monocyte count/HDL-C data, yielding 3,004 patients. MHR was calculated as monocyte count (×109/L) divided by HDL-C (mmol/L). The primary outcome was 1-year all-cause mortality. Kaplan-Meier analysis and log-rank tests compared survival across MHR tertiles. Restricted cubic splines assessed dose-response relationships. Multivariable Cox proportional hazards regression with progressive adjustment evaluated MHR-mortality associations. Subgroup analyses examined effect modification across predefined clinical characteristics.ResultsThe cohort had a mean age of 73.5 years, with 65.8% males. Patients in the highest MHR tertile (T3) demonstrated greater disease severity, higher comorbidity burden, and more intensive treatment requirements. Kaplan-Meier analysis revealed significantly lower 1-year survival in T3 versus T1 (68% vs. 80%, log-rank P<0.001). Restricted cubic spline analysis showed a linear relationship (P for non-linearity=0.441). After adjustment for demographics, vital signs, comorbidities, laboratory parameters, and treatments, each 1-unit increase in MHR conferred a HR of 1.33 (95% CI: 1.18-1.51), per-SD HR = 1.10, 95% CI: 1.03-1.17. Tertile analysis demonstrated a dose-response pattern, with T3 showing HR=1.25 (95% CI: 1.04-1.51) compared with T1 (P for trend<0.05). Subgroup analyses revealed consistent associations across most strata.ConclusionsElevated MHR is associated with increased 1-year mortality in critically ill CHD patients. As a readily available composite marker, MHR may have supplementary prognostic relevance, but its clinical utility requires prospective validation.