Although successful, percutaneous coronary interventions (PCI) with stent implantation may be hampered by periprocedural myocardial necrosis. In acute ST-elevation myocardial infarction (STEMI), the reduction of thrombus burden through manual thrombus aspiration (TA) of an occluded coronary artery has been documented to produce an improved myocardial perfusion rate and significant survival advantage. To date, beyond feasibility and safety studies no clinical benefit has been yet documented with the use of TA before stent deployment in the setting of acute coronary syndromes (ACS) outside acute STEMI. The investigators hypothesize that TA before stent deployment reduces the thrombus/plaque burden - as assessed by intravascular imaging systems - in the setting of acute coronary syndromes (ACS) outside acute STEMI.

Periprocedural myocardial infarction (MI) has an independent adverse prognostic relevance. Several trials have documented a reduction in the occurrence of periprocedural MI through various pharmacological strategies, with enhanced inhibition of platelet aggregation or high dose statins. However, real-world registries still document an incidence of periprocedural MI in 30-40% of patients. Currently available intravascular imaging techniques, Intravascular Ultrasound (IVUS) and more recently available Optical Coherence Tomography (OCT) allow a precise evaluation of the coronary plaque and can be extremely useful for monitoring plaque modifications obtained with thrombus aspiration (TA). Plaque burden will be assessed as plaque + media (P+M), commonly measured with IVUS by subtracting lumen (L) to external elastic membrane (EEM) cross sectional area (P+M= EEM-L).

Expecting a mean plaque volume of 160±50 mm3 in a population of patients with ACS undergoing PCI, a sample size of at least 45 patients (52 lesions) with a recent (<15 days, but after 24 hours) STEMI or a non-ST elevation (NSTE)-ACS within 72 hours of symptoms would provide a 90% power to detect a 20% reduction in the plaque volume after TA with an alpha (probability value) of 0.05.

Inclusion Criteria:

• Age between 18-75 years old.
• Recent(<15 days, >24 hrs)STEMI or NSTE-ACS within 72 hrs of symptoms.
• Presence at least one "culprit" high-grade (>90%)lesion.

Exclusion Criteria:

• STEMI within 24 hours.
• Cardiogenic shock, decompensated heart failure, LVEF<30%.
• Serum creatinine ≥ 2.5 mg/dl.
• Contraindication to aspirin, heparin, thienopyridines.
• Total occlusion of target vessel.
• Diseased vein graft or a restenosis.

45 patients with at least one "culprit" lesion, identified as a high-grade (>90%) lesion in the territory of jeopardized myocardium, at coronary angiography performed for a recent (<15 days, but after 24 hours) STEMI or a non-ST elevation (NSTE)-ACS within 72 hours of symptoms.