Randomization will be performed after initial coronary angiography, once the operator has identified the lesion responsible for the ACS. Patients will be randomly allocated to one of two groups. In the "Control" Group, the angioplasty procedure will be guided by traditional fluoroscopy alone.

In both groups, fractional flow reserve (FFR) will be measured at the end of the procedure, once the operator considers the result of the angioplasty to be optimal. The average of three consecutive FFR measures will be recorded.

Randomization will be performed after initial coronary angiography, once the operator has identified the lesion responsible for the ACS. Patients will be randomly allocated to one of two groups.

In the "OCT" group, OCT will be performed to optimise the results of angioplasty. The procedure will be performed according to usual practice, with or without pre-dilation before implantation of one or more stents (drug-eluting or bare metal). In the OCT group, OCT will be performed after initial coronary angiography and at the end of the procedure and the operator will have the possibility to change procedural strategy according to the data immediately available on the OCT images, with the possibility of additional interventions (additional balloon inflations, addition stent implantation, use of GPIIb/IIIa inhibitors and/or thromboaspiration and/or rotational atherectomy).

Optical Coherence Tomography (OCT) is a recent imaging modality that yields cross-sectional images with a resolution 10 times greater than that of intravascular ultrasound (IVUS). OCT uses a near-infra-red light source to obtain images of the interior walls of the coronary arteries and is increasingly used to evaluate vulnerable atherosclerotic plaques and assess placement and response to stenting.

OCT images are acquired by automated pullback over 2 to 3 seconds of the light source that yields a helicoidal image of a longitudinal segment of 50 mm. Intravascular imaging is obtained by injecting contrast medium or saline solution.

Evaluation of the functional result of the angioplasty procedure as assessed by fractional flow reserve (FFR) at the end of the procedure.

The average of three consecutive FFR measures will be recorded.

Assessed by the presence of any one or more of the following criteria:

Incomplete coverage of the lesion by the stent, Residual stenosis upstream or downstream from the stent, Edge dissection, Presence of thrombus, Tissue protrusion through the stent struts, Stent Malapposition.