Higher remnant cholesterol to lymphocyte ratio is associated with vulnerable plaque features in acute coronary syndrome

Background Remnant cholesterol to lymphocyte ratio (RCLR) integrates atherogenic lipid metabolism and systemic inflammation, potentially reflecting plaque vulnerability in acute coronary syndrome (ACS). However, its association with intracoronary imaging features remains unclear. This study aimed to investigate the relationship between RCLR and culprit plaque characteristics using optical coherence tomography (OCT). Methods This retrospective study analyzed 450 ACS inpatients (2021–2024), with 201 included after rigorous selection. The patients were classified into three groups based on the remnant cholesterol to lymphocyte ratio [RCLR; remnant cholesterol (RC = TC−HDL-C−LDL-C) divided by lymphocyte percentage], using tertiles: Group T1 (RCLR ≤ 3.03, n = 66), Group T2 (3.03 < RCLR ≤ 4.66, n = 68), and Group T3 (RCLR > 4.66, n = 67). The characteristics of the culprit lesion plaques were assessed using OCT, and differences among the groups, the correlation between RCLR and plaque characteristics, and multivariable logistic regression were analyzed using SPSS version 27.0 and Python, with two-sided statistical significance set at p < 0.05 (with Bonferroni correction for post-hoc pairwise comparisons). Results OCT imaging analysis revealed significant differences in qualitative features among various RCLR groups, including plaque rupture, lipid plaque, thin-cap fibroatheroma (TCFA), and superficial calcification (all p values < 0.05). In an exploratory analysis restricted to lesions containing lipid plaque, RCLR showed weak positive correlations with the maximum lipid arc ( r = 0.252, 95% CI: 0.026–0.454, p = 0.022) and the lipid index ( r = 0.279, 95% CI: 0.062–0.481, p = 0.011). Receiver operating characteristic (ROC) curve analysis further confirmed that RCLR had modest discriminatory value for lipid plaques (AUC = 0.635, 95% CI: 0.559–0.712, p = 0.001), TCFA (AUC = 0.646, 95% CI: 0.559–0.733, p = 0.003), and plaque rupture (AUC = 0.618, 95% CI: 0.540–0.696, p = 0.004). In multivariable analysis, the highest RCLR tertile remained associated with lipid-rich plaque, TCFA, and plaque rupture after adjustment for major clinical risk factors (all P for trend ≤ 0.011). Conclusion In ACS patients, a higher RCLR was associated with high-risk plaque characteristics detected by OCT, such as lipid-rich plaques, TCFA, and plaque rupture, and the highest RCLR tertile remained associated with these features after multivariable adjustment. RCLR exhibits a certain predictive ability for these vulnerable plaque features. Higher RCLR tertiles were associated with a greater prevalence of vulnerable plaque features, suggesting that RCLR may serve as a composite lipid–inflammatory marker associated with coronary plaque vulnerability, although its signal partly overlaps with systemic inflammatory-cell parameters.