A Novel Atherogenic Index Is Associated with Multivessel Coronary Disease in Patients Undergoing Invasive Coronary Angiography: A Cross-Sectional Retrospective Study

Background/Objectives: Multivessel coronary artery disease (MVCD) determines prognosis and revascularization strategy. The CRP × 100/HDL-C atherogenic index (AtI) integrates systemic inflammation and anti-atherogenic lipoprotein parameters. We evaluated its capacity to predict MVCD in patients undergoing invasive coronary angiography (CA). Materials and Methods: Retrospective cross-sectional study of a cohort of 204 patients with suspected ischemic heart disease. The 173 patients who underwent invasive CA as a diagnostic test were classified as having no significant lesions (n = 55), single-vessel disease (n = 69), or MVCD (n = 49). The new AtI was measured as CRP (mg/dL) × 100/HDL-C (mg/dL). Kruskal-Wallis with Bonferroni correction, ROC analysis with DeLong confidence intervals, adjusted logistic regression (log2-transformed), and Harrell bootstrap optimism correction (1000 iterations) were applied. Results: The AtI showed a progressive gradient: median 0.73 (IQR 0.57–1) in the no-lesions group, 1.71 (IQR 0.95–2.44) in the single-vessel group, and 2.86 (IQR 1.79–6.67) in the MVCD group (Kruskal-Wallis p < 0.001), Spearman ρ = 0.596 (p < 0.001), and all Bonferroni-corrected pairwise comparisons significant. AUC for MVCD prediction: 0.818 (95% CI 0.753–0.883), superior to Castelli I (0.685; DeLong p = 0.003), Castelli II (0.626; p < 0.001), and the plasma atherogenic index (0.708; p = 0.013). At cut-off ≥2.00 (Youden criterion): sensitivity 73.5%, specificity 78.2%, NPV 88.2%. The AtI was independently associated with MVCD in adjusted logistic regression (OR 2.84 per doubling; 95% CI 1.95–4.13; p < 0.001). Adding the AtI to a classical risk factor model increased AUC from 0.652 to 0.836 (ΔAUC +0.184; 95% CI 0.093–0.275; p < 0.001; optimism-corrected AUC 0.812). Conclusions: The CRP × 100/HDL-C AtI is independently associated with MVCD and adds discrimination to a clinical model. It is a simple and inexpensive marker of angiographic extent; a cut-off of ≥2 had an NPV of 88.2% (86.5% after optimism correction), and its clinical usefulness requires external and prospective validation.