Atherogenic Dyslipidemia and the Atherogenic Index of Plasma in Premature Acute Myocardial Infarction: A Comprehensive Comparison of Derived Lipid Indices, Systemic Inflammation, and the TG-Glucose Axis in a Semi-urban Region

Background The Atherogenic Index of Plasma (AIP) is a validated marker of small-dense low-density lipoprotein (LDL) particle predominance and insulin resistance. AIP has not been systematically assessed in premature acute myocardial infarction (AMI) in South Asian populations with a comprehensive panel of derived atherogenic indices. A previous study identified isolated hypertriglyceridemia as the predominant lipid phenotype of premature AMI. Therefore, this study evaluates conventional lipid parameters, together with derived atherogenic indices like the triglyceride (TG) to high-density lipoprotein (HDL) (TG:HDL) ratio, Atherogenic Index of Plasma (AIP), and non-HDL cholesterol, which provide better insights into the metabolic status of premature patients. The relationship between triglycerides, glucose, and inflammation in the semi-urban Indian population remains incompletely understood. Methods A total of 55 participants were enrolled: 25 healthy controls, 13 premature AMI patients (age ≤45 years), and 17 old-age AMI patients (age >45 years). AIP was calculated as log₁₀ (TG/HDL). Additional derived indices included very-low-density lipoprotein (VLDL) (TG/5), TG:HDL ratio, Atherogenic Index of Plasma (TG-HDL/HDL), non-HDL cholesterol, Castelli Risk Index (total cholesterol/HDL), and LDL:HDL ratio. Group comparisons used Kruskal-Wallis and Mann-Whitney U tests. Pearson and Spearman correlations examined TG/Atherogenic Index relationships with glycaemic markers by age group. Area under the receiver operating characteristic curve (AUROC) analysis compared the discriminative performance of all indices for premature AMI versus controls and old-age AMI versus controls. Results AIP was significantly elevated in premature AMI (mean 0.414±0.429) versus controls (0.183±0.217; p=0.008**) and versus old-age AMI (0.171±0.185; p=0.012*), with no significant difference between old age AMI and controls (p=0.764). The AIP high-risk threshold age (>0.24) was exceeded by 62% of premature AMI patients versus 24% of controls and 24% of old age AMI patients. AIP correlated significantly with fasting blood sugar (FBS) (r=0.686, p=0.010 **) and glycated hemoglobin (HbA1C) (r=0.633, p=0.020*) exclusively in premature AMI, a pattern absent in old age AMI and controls. AUROC for AIP was 0.791 (premature AMI vs controls) versus 0.541 (old-age AMI vs controls), suggesting strict age-specificity. High-sensitivity C-reactive protein (Hs-CRP) remained the strongest overall discriminator (AUROC=0.863 for premature AMI; AUROC=0.974 for old-age AMI). Among lipid indices, HDL (AUROC=0.815) and AIP (0.791) outperformed TG:HDL ratio (0.763), TG alone (0.728), and Castelli Index (0.615) for premature AMI discrimination. Conclusions The AIP, computed as log₁₀(TG/HDL), is a superior single lipid index for identifying the premature AMI phenotype compared to standard lipid parameters. Its tight coupling with glycaemic markers exclusively in premature AMI patients suggests that subclinical insulin resistance is the primary metabolic driver, and its age-specificity is present in premature AMI but not in old-age AMI, validating AIP as a targeted screening index for the premature AMI phenotype. Together with Hs-CRP and fasting glucose, the Atherogenic Index of Plasma (AIP) outperforms standard lipid measures in identifying premature AMI and should be included in routine cardiac risk assessments for high-risk young South Asian adults.