Prognostic Value of the Atherogenic Index of Plasma for Severity and Cardiovascular Outcomes in Young Patients (≤35 Years) with Coronary Artery Disease: A Retrospective Study

Background: Rising coronary artery disease (CAD) in young adults calls for early risk stratification, yet the atherogenic index of plasma (AIP) has been understudied in patients aged ≤35 years. We therefore assessed its association with coronary lesion severity and major adverse cardiovascular events (MACE) in this cohort. Methods: This single-center retrospective study enrolled 948 patients aged 18–35 years with angiographically confirmed CAD. Greater coronary lesion severity was defined as a Gensini score > 40. The association between AIP and MACE was explored. Results: During a median follow-up of 60 months, MACE occurred in 287 patients. After full adjustment, AIP as a continuous variable was independently associated with greater coronary lesion severity (OR = 1.761; 95% CI: 1.052–2.948; p = 0.031). Regarding prognosis, when AIP was dichotomized at 0.4, it was independently associated with MACE (HR = 1.350; 95% CI: 1.060–1.721; p = 0.015) in the fully adjusted model, whereas continuous AIP did not retain significance. Restricted cubic spline analysis suggested a possible U-shaped dose–response relationship between AIP and MACE (overall p < 0.001, nonlinear p = 0.051). Subgroup analyses showed that the association of AIP with MACE was generally consistent across all examined strata, with no significant interactions (all p for interaction >0.05). Conclusions: AIP was independently associated with greater coronary lesion severity and MACE in young CAD patients (≤35 years). These findings support AIP as a practical tool not only for early risk stratification but also for guiding intensive lipid-lowering therapy in this distinct population.