Prospective, multicenter, randomized, double-blind, placebo-controlled trials.

A total of 3486 subjects with ACS who met inclusion criteria and do not have any exclusion criterion will be randomized to IVUS- or Angiography-guidance group (first randomization). In the IVUS-guidance group, IVUS will be used to evaluate the lesion's specificity and to measure lesion length, landing zone, and reference vessel diameter prior-to stenting; and to assess stent expansion, extension, apposition, and possible complications after stent implantation. The IVUS- defined criteria for the optimal stent deployment included: 1) the minimal stent area (MSA) in the stented segment is >5.0 mm^2, or 90% of the MLA at the distal reference segments; 2) plaque burden 5-mm proximal or distal to the stent edge is <55%; and 3) absence of >Type B edge dissection. Further treatment will be required if stenting procedure is defined as suboptimal according to IVUS definition. IVUS will be not allowed to be used in the Angiography-guidance group.

Those patients who have had no death, STEMI, stroke, ST, TVR or major bleeding (BARC 3 or 5) within 30 days and have continued on aspirin and ticagrelor for 30 days without interruption for >48 hours will be randomized 1:1 to:

1. Ticagrelor plus+ matching placebo for an additional 11 months (SAPT group)
2. Ticagrelor plus aspirin (study drug) for an additional 11 months (DAPT group) Follow-up of all subjects will continue for 1 year with an option for additional follow-up to 3 years.

Inclusion Criteria:

Enrollment into the study will require meeting at least one of these clinical syndromes within 1 month.

• Unstable angina, defined as rest pain for 5-30 minutes or deteriorative exertional angina with either a) transient ST segment depression or elevation, or b) angiography showing a visually estimated diameter stenosis ≥90% or a ruptured plaque or thrombotic lesion
• Non-ST elevation myocardial infarction (NSTEMI), defined as positive troponin consistent with clinical syndrome.
• ST elevation MI (STEMI)

Exclusion Criteria:

• Unable or unwilling to provide informed consent
• Stroke within 3 months or any permanent neurologic deficit, and prior intracranial bleed, or any intracranial disease such as aneurysm or fistula
• Previous coronary artery bypass graft (CABG)
• Any planned surgery within 90 days
• Any reason why any antiplatelet therapy might need to be discontinued within 12 months
• Severe chronic kidney disease defined as an estimated glomerular filtration rate (eGFR) < 20 ml/min/1.73m^2
• Need for chronic oral anticoagulation (warfarin/coumadin or direct oral anticoagulants)
• Platelet count < 100,000 mm^3
• Contraindication to aspirin
• Contraindication to ticagrelor
• Liver cirrhosis
• Women of child-bearing potential
• Life expectancy < 1 year
• Any condition likely to interfere with study processes including medication compliance or follow-up visits (e.g. dementia, alcohol abuse, severe frailty, long distance to travel for follow-up visits, etc.)