Inclusion criteria

Patients presenting for ACS who underwent IVUS during diagnostic interventions

IVUS run carried out for borderline lesions evaluation (no tight stenosis).

IVUS run included segment of interest (lesion) and at least one reference vessel segment

IVUS run considered suitable for analysis with automatic pull back

Exclusion criteria

IVUS run carried out for the evaluation of a stent, acutely or previously implanted

IVUS run not including at least one of the two reference segments

IVUS run with manual pull back

IVUS run with >40% superficial arc of calcification on more than 50% of lesion length

IVUS run interrupted by side branches >1.5 mm in diameter

IVUS run considered inadequate technically