The aim of this study is to study whether the use of complex 3-dimensional assessment of the severity of a stenosis improves angina and in general cardiovascular outcomes in patients who have residual intermediate coronary artery stenosis following an acute coronary syndrome (ACS) treated with percutaneous coronary intervention (PCI).

Goals of the study are:

• To investigate whether decision-making based on quantitative flow reserve (QFR) is associated with a decrease in angina 3 months after an ACS
• To investigate whether use of QFR is associated with an improved prognosis.

The study is a single-center, randomized superiority trial to compare two strategies for the assessment of the hemodynamic relevance of coronary lesions.

The primary analysis will be on the per-protocol principle (i.e. including all patients who are not protocol violators). A separate analysis will be performed on an intention-to-treat basis (i.e. all randomized patients randomized to a treatment arm).

Primary endpoint 1. Angina questionnaire

Secondary endpoints:

Number and % of patients undergoing PCI

Seattle Angina Questionnaire

• SAQ Physical limitation scale
• SAQ angina stability scale
• SAQ angina frequency scale
• SAQ quality of life
• SAQ Treatment Satisfaction Disease perception scale Follow-up (3 and 12 months) - Patient-oriented composite endpoint (death, myocardial infarction, unplanned revascularization) and its components.

Inclusion Criteria:

• Successfully treated acute coronary syndrome
• At least one additional intermediate stenosis (>30% and <90%).
• Patient ≥18 years old

Exclusion Criteria:

• Stenoses or patients a priori not amenable to treatment with PCI (at the discretion of two interventional cardiologists - e.g. patients with limited life expectancy, stenosis in very small vessels, very diffuse disease with complex/very calcified stenosis requiring surgery etc).
• Persistent symptoms or evidence of ischemia requiring intervention of the non-culprit lesion.
• Any contraindication to PCI according to guidelines
• An ACS in the period following the index ACS and randomization
• TIMI (Thrombolysis in Myocardial Infarction) flow grade < 3 in the culprit vessel
• Presence of thrombus in the non-culprit lesion
• Participation in another randomized interventional study interfering with the present protocol
• Patient unable to give informed consent
• Women of child-bearing potential or lactating
• Previous coronary artery bypass surgery CABG
• Recent (within 30 days) unsuccessful PCI
• Decompensated congestive heart failure (CHF) or hospitalization due to CHF during the last 3 months
• Left ventricular ejection fraction <30%
• Severe chronic obstructive pulmonary disease (COPD)
• Severe valvular heart disease
• FFR (or RFR, iFR etc) assessment of non-culprit lesions at the time of the index procedure

Patients and outcome assessors will be blinded to the randomization group.