Association of low triglyceride glucose-body mass index (TyG-BMI) and high systemic inflammation response index (SIRI) with one-year all-cause mortality in critically ill patients with coronary heart disease: a retrospective cohort study from MIMIC-IV

Insulin resistance (IR) and systemic inflammation are key drivers of coronary heart disease (CHD), yet their combined prognostic value in critically ill patients remains unknown. The triglyceride glucose-body mass index (TyG-BMI) is a novel IR surrogate, and the systemic inflammation response index (SIRI) reflects global inflammatory burden. This study aimed to evaluate the independent and combined associations of TyG-BMI and SIRI with one-year all-cause mortality in critically ill CHD patients. This retrospective cohort study extracted data from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Cox proportional hazards models and restricted cubic splines (RCS) were used as primary analyses to assess the associations of continuous TyG‑BMI and SIRI with one‑year all‑cause mortality, including formal interaction testing. A four‑group comparison based on median splits was additionally performed as a secondary, exploratory analysis to illustrate descriptive risk patterns. A total of 1,546 CHD patients (60.87% male; mean age 70.90 ± 13.04 years) were included, with a one‑year mortality rate of 37.45% (579 deaths). In the primary continuous analyses, higher SIRI was associated with higher one‑year mortality (HR 1.023 per 0.1-unit increase, 95% CI 1.018–1.027, P < 0.0001), whereas higher TyG‑BMI was associated with lower mortality (HR 0.998 per unit increase, 95% CI 0.997–0.999, P = 0.0008); the multiplicative interaction between TyG‑BMI and SIRI was not statistically significant (P = 0.3668). In an exploratory four‑group analysis based on median splits (median TyG‑BMI, 277.66; median SIRI, 6.64), using the TyG‑BMI < median & SIRI < median group as the reference, patients with TyG‑BMI < median & SIRI > median had the highest mortality risk (HR 2.33, 95% CI 1.85–2.94, P < 0.0001), while those with TyG‑BMI > median & SIRI < median had the lowest risk (HR 0.65, 95% CI 0.48–0.87, P = 0.0037). RCS analysis revealed a significant non‑linear relationship between SIRI and mortality (P for non‑linearity < 0.0001); the hazard ratio increased rapidly at low SIRI values, plateaued gradually, and declined slightly at higher values. TyG‑BMI showed no significant non‑linear association (P = 0.1430). No significant effect modification was observed across the tested subgroups (all interaction P > 0.05). In critically ill CHD patients, low TyG‑BMI combined with high SIRI identifies a high‑risk phenotype with more than double the one‑year mortality risk. These observational, single-database findings require external validation before any clinical application can be considered. CHD is a leading cause of death worldwide. Insulin resistance and inflammation drive its progression. TyG‑BMI is a validated surrogate for insulin resistance, and SIRI reflects systemic inflammation. Previous studies have evaluated these indices separately. Their combined prognostic value in ICU patients remains unexamined. This study evaluated the independent and combined associations of TyG-BMI and SIRI with one-year all-cause mortality in critically ill CHD patients, including formal interaction testing and dose-response analyses, and asked whether a dual metabolic-inflammatory phenotype identifies a high-risk subgroup. This is the first study to simultaneously evaluate TyG‑BMI and SIRI in critically ill CHD patients. Higher SIRI was associated with higher one‑year mortality in both continuous and exploratory four-group analyses (low TyG‑BMI + high SIRI versus low‑low group: HR 2.33), with a significant non-linear dose-response pattern; the multiplicative interaction between the two indices was not statistically significant. The inconsistent signal of TyG‑BMI alone cautions against overinterpreting the “reverse metabolic paradox.” Using routine admission laboratory tests, we identified a high‑risk metabolic-inflammatory phenotype in critically ill CHD patients. These findings are observational and hypothesis-generating; whether incorporating TyG-BMI and SIRI into routine risk assessment improves clinical decision-making requires prospective validation.