Identification of near-infrared spectroscopy-defined lipid content within calcified coronary plaques using optical coherence tomography

Background and Aims Calcified coronary plaques frequently harbor lipid-rich components, yet identifying residual lipid burden within calcification remains challenging. This study aimed to evaluate the ability of optical coherence tomography (OCT) to identify lipidic calcification, utilizing near-infrared spectroscopy intravascular ultrasound (NIRS-IVUS) as the reference standard. Methods We retrospectively analyzed patients undergoing PCI for de novo calcified lesions (IVUS arc ≥90°) assessed by both NIRS-IVUS and OCT. Lipidic calcification was defined as a lesion with a maximum lipid core burden index in 4 mm (maxLCBI4mm) ≥400. On OCT, the "attenuated calcium index" was calculated as the mean angle of calcification exhibiting an invisible trailing edge across the 20-mm lesion segment. We compared clinical and imaging characteristics between vessels with and without lipidic calcification. Results Among 102 patients, 38 lesions (37.3%) exhibited lipidic calcification. While clinical demographics were comparable between groups, OCT analysis revealed significantly greater lipid length, attenuated calcium index, and prevalence of cholesterol crystals in the lipidic calcification group. Multivariable analysis identified the attenuated calcium index (OR 1.03; 95% CI 1.01–1.05) and cholesterol crystals (OR 10.5; 95% CI 2.91–37.9) as independent predictors of lipidic calcification. Furthermore, among calcified nodules, eruptive nodules demonstrated a significantly higher maxLCBI4mm than non-eruptive ones (401 vs. 208; p=0.035). Conclusions The OCT-derived attenuated calcium index and cholesterol crystals are distinct markers associated with lipidic calcification. Additionally, eruptive calcified nodules appear to harbor a greater lipid burden. OCT facilitates the identification of high-risk phenotypes even within complex calcified lesions.