Comparative value of metabolic and inflammatory indices for identifying OCT-derived coronary plaque vulnerability in patients with acute coronary syndrome and type 2 diabetes mellitus

Background/objectives Patients with acute coronary syndrome (ACS) and type 2 diabetes mellitus (T2DM) are prone to coronary plaque vulnerability and recurrent ischemic events. Although optical coherence tomography (OCT) enables a detailed assessment of vulnerable plaque features, it is invasive and not routinely applicable in all patients. Several routinely available metabolic and inflammatory indices have been associated with cardiovascular risk; however, their comparative value in identifying OCT-defined vulnerable plaques in patients with ACS and T2DM remains unclear. Methods This single-center retrospective study included 115 patients with ACS and T2DM who underwent OCT assessment of one target coronary lesion between July 2024 and May 2025 at our institution. Candidate biomarkers included the triglyceride-glucose (TyG) index, fasting blood glucose (FBG), triglycerides (TG), atherogenic index of plasma (AIP), TG/high-density lipoprotein cholesterol (TG/HDL-C) ratio, glycated hemoglobin (HbA1c), and selected inflammatory indices. The primary outcome was OCT-defined thin-cap fibroatheroma (TCFA), and fibrous cap thickness (FCT) was analyzed as a key continuous OCT parameter. Logistic regression, linear regression, and receiver operating characteristic analyses were performed to compare the associations and discriminative abilities of the candidate biomarkers. Results TCFA was identified in 63 (54.8%) of the 115 patients. Compared with patients without TCFA, those with TCFA had higher levels of TG, FBG, HbA1c, TyG, AIP, and TG/HDL-C, whereas the neutrophil-to-lymphocyte ratio and systemic immune-inflammation index did not differ significantly between the groups. After multivariable adjustment, TyG index showed the most consistent association with TCFA among the evaluated biomarkers (odds ratio per 1-SD increase, 4.42; 95% confidence interval, 2.34−8.35; P < 0.001). TyG was also inversely associated with FCT, a continuous component underlying TCFA classification (adjusted beta per 1-SD increase, −19.0 μm; 95% confidence interval, −25.5 to −12.4 μm; P < 0.001). In exploratory single-biomarker receiver operating characteristic analysis, TyG had the largest numerical discriminative estimate for TCFA (area under the curve, 0.792; 95% confidence interval, 0.711−0.874), followed by FBG, TG, AIP, and TG/HDL-C. Inflammatory indices showed limited ability to discriminate TCFA. Conclusions Among the routinely available metabolic and inflammatory indices, TyG index showed the most consistent association with OCT-defined coronary plaque vulnerability in patients with ACS and T2DM and had the largest numerical AUC in exploratory single-biomarker discrimination analyses. These findings suggest that TyG is an accessible metabolic correlate of OCT-defined plaque vulnerability in this high-risk cohort; however, larger prospective studies are needed for confirmation.