Impact of small dense low-density lipoprotein cholesterol on cholesterol crystals in patients with acute coronary syndrome: An optical coherence tomography study

•Sd-LDL-c was an independent risk factor of cholesterol crystals (CC).•The levels of sd-LDL-c, apolipoprotein C3, and HbA1c were associated with CC.•The presence of CC is associated with vulnerable plaques, such as ruptured plaques.•A negative correlation was found between sd-LDL-c levels and CC-depth.•Sd-LDL-c increased significantly with increased macrophage grade.