Early Creatinine-Defined Acute Kidney Injury and 1-Year Mortality in Critically Ill AMI-Coded Patients Meeting Premature-Age Criteria: A MIMIC-IV Retrospective Cohort Study

Objective: Acute kidney injury may complicate acute myocardial infarction and has prognostic significance in broad acute coronary syndrome cohorts. However, the timing of early kidney injury and the prognostic differentiation among acute kidney injury phenotypes remain insufficiently characterized in critically ill patients with acute myocardial infarction who meet premature-age criteria and require intensive care.
Method: This retrospective cohort study used MIMIC-IV, a deidentified, single-center critical care database from an academic health system in the United States. The study cohort should be interpreted as ICU-admitted patients with AMI codes who met prespecified sex-specific premature-age criteria rather than as a general young or angiographically adjudicated premature myocardial infarction population. Premature myocardial infarction was prespecified as age younger than 55 years in men and younger than 65 years in women. The primary exposure was early creatinine-defined acute kidney injury reconstructed according to the KDIGO serum creatinine relative and absolute change criteria, with the first qualifying creatinine-based onset occurring within 0–48 hours after ICU admission. Urine-output and renal-replacement-therapy variables were derived separately for phenotype analyses and were not incorporated into the primary exposure. The primary outcome was 1-year all-cause mortality. The main analysis used a time-dependent Cox model, with landmark phenotype analyses performed as supportive analyses.
Results: The cohort included 1261 patients, of whom 363 (28.8%) developed early creatinine-defined acute kidney injury. Within 1 year, 275 patients died (21.8%), including 151 deaths during the index hospitalization (12.0%). Early creatinine-defined acute kidney injury was associated with higher mortality in the primary time-dependent Cox model (hazard ratio 1.37, 95% confidence interval 1.06–1.79; P=0.018). The association was also maintained in the supportive parsimonious multivariable Cox model (hazard ratio 1.63, 95% confidence interval 1.23–2.16; P<0.001). The expanded complete-case model and prespecified multiple-imputation sensitivity analysis also supported an association in the same direction. In the 24-hour landmark analysis, the urine-output-only acute kidney injury phenotype did not retain an independent association with mortality, whereas the creatinine- or renal-replacement-therapy-positive phenotype remained directionally associated with higher risk.
Conclusion: Early creatinine-defined acute kidney injury may serve as a marker of increased risk among ICU-admitted, AMI-coded patients who meet sex-specific premature-age criteria. The findings should not be generalized to all young or premature myocardial infarction patients and should be interpreted cautiously in view of ICU-only selection, coding-based disease definitions, incomplete etiologic profiling, and residual confounding.

Keywords: Acute kidney injury, critical care, MIMIC-IV, mortality, premature-age myocardial infarction.