Progression of Protruding Plaque in Acute Coronary Syndrome Diagnosed by Serial Optical Coherence Tomography

<b>Background:</b> Plaque protrusion after stent implantation is frequently observed in acute coronary syndrome (ACS) patients, yet studies on its long-term progression and clinical significance are limited. <b>Methods:</b> Seventy-eight ACS patients underwent optical coherence tomography (OCT)-guided PCI and follow-up OCT at 1 year. A total of 101 protruding lesions were classified into atherogenic neointima (AN) and non-AN groups based on OCT findings. Qualitative and quantitative assessments of protruding plaque, including irregularity and plaque intensity, were conducted. <b>Results:</b> AN developed in 17% of irregular protrusion (IP) lesions, whereas no smooth protrusion progressed to AN. Lesions in the AN group showed greater increases in protruding plaque volume (2.80 ± 0.46 mm² vs. 0.67 ± 0.16 mm², <i>p</i> < 0.001) and diameter stenosis (16.5% vs. 10.1%, <i>p</i> = 0.02). Follow-up LDL levels were higher in the AN group compared with the non-AN group (76.9 vs. 61.2 mg/dL, <i>p</i> = 0.02), despite similar baseline levels. <b>Conclusions:</b> Low-intensity IP after stent implantation in ACS patients carries a high risk of progression to AN, particularly under poor LDL control. Aggressive lipid-lowering therapy may mitigate this risk.