Intracoronary Cryotherapy Effect on Stabilization of Vulnerable Plaque in Patients With NSTEMI or Unstable Angina (POLARSTAR)

Inclusion Criteria: Subject is at least 18 years old. Subject has acute cardiac pain/angina consistent with acute coronary syndrome eligible for coronary angiography meeting one of the following criteria: Non-ST-segment elevation myocardial infarction (NSTEMI) with rise/fall of cardiac enzymes (troponin I or T) with at least one value above the 99th percentile of the upper reference limit requiring PCI within 72 hours from diagnosis Unstable angina Successful PCI (defined as diameter stenosis less than 30% and TIMI 3 flow on final angiography without procedural complication) of the culprit lesion. Subject has at least one high-risk plaque meeting the criteria below: Located in a non-culprit vessel, High-risk plaque lesion on CCTA and at least one of the following features: Presence of low-attenuation plaque (HU<50) and/or Positive remodelling (remodelling index >1.1) and/or Napkin ring sign and/or Plaque burden ≥70% Lesion length ≤ 20 mm. Diameter stenosis on invasive angiography between 30% and 70% on coronary angiogram or negative physiology assessment (FFR>0.80 or non-hyperemic pressure ratios (NHPR) >0.89). Reference vessel diameter (RVD) < 3.75 mm and > 2.00 mm in diameter Investigator considers that lesions are accessible. If more than two suitable lesions available, investigator will select the most appropriate lesion for cryotherapy treatment. Subject is able to provide consent and has signed and dated the informed consent form. Exclusion Criteria: Subject is hemodynamically unstable (cardiogenic shock, hypotension needing inotropes, hypoxia needing intubation, refractory ventricular arrhythmias, and IABP). Subject has ongoing ST-segment elevation myocardial infarction. Subject had a procedural complication during the Acute coronary syndrome (ACS) PCI procedure. Subject has history of Coronary Artery Bypass Graft (CABG) or planned CABG within 12 months after the index procedure. Subject has known reduced Left Ventricular Ejection Fraction < 30%. Subject has known severe valvular heart disease. Subject has known severe renal insufficiency (eGFR <30 ml/min/1.72 m2). Subject has any life-threatening conditions or medical comorbidity resulting in life expectancy < 12 months. Subject is currently participating in another clinical investigation that has not yet reached its primary endpoint. Subject is pregnant or lactating, or NOT surgically sterile (tubal ligation or hysterectomy) or NOT postmenopausal for at least 6 months or is a female with childbearing potential without effective contraception (pill, patch, ring, diaphragm, implant and intrauterine device). Angiographic exclusion criteria: Visible distal embolization/no-reflow following culprit lesions PCI. Left main coronary artery disease (visual diameter stenosis > 50%). Stent thrombosis/restenosis as a culprit lesion. CTS lesion involving a bifurcation (defined as lesions involving side branches >2.0 mm). Angiographic or CCTA evidence of severe calcification and/or marked tortuosity of the index vessel and/or lesion. Thrombotic lesions Ostial lesions