Thinning of fibrous cap in atherosclerotic plaques is associated with plaque vulnerability. The high resolution of optical coherence tomography (OCT) provides an accurate measurement of fibrous cap thickness. Endothelial dysfunction is a key component of vulnerable plaque and digital reactive hyperemia-peripheral arterial tonometry (RH-PAT) is a non-invasive automatic and quantitative method to evaluate endothelial function. The investigators will investigate the association between endothelial function assessed by RH-PAT and plaque vulnerability determined by OCT-derived thin-cap fibroatheroma (TCFA).

Consecutive patients with acute coronary syndrome (ACS) who undergo both OCT examination and RH-PAT examination are enrolled. OCT examination is performed to observe the culprit lesion before percutaneous coronary intervention, and endothelial function is evaluated using RH-PAT before discharge.

Inclusion Criteria:

• patients with angiographically proven ACS (luminal stenosis of at least 50%) who undergo both OCT examination before coronary stent implantation and RH-PAT examination before discharge.

Exclusion Criteria:

• none

Yokohama City University Medical Center