Recently, a new device for measuring physiological lesion severity, the pressure microcatheter, was introduced. The pressure microcatheter provides similar information to the conventional measurement technique but differs as it is easily advanced on a customary coronary wire and simplifies pullback maneuvers. The pressure microcatheter has been shown to provide comparable FFR results to pressure wires. Insightful-FFR is an investigator-driven, multicenter, randomized, open-label and prospective trial of patients with stable coronary artery disease or stabilised non-ST elevation acute coronary syndrome (ACS) with epicardial stenosis considered for PCI aiming at comparing clinical outcomes between pressure microcatheter and pressure wire-guided strategies. The study hypothesis states that the use of a Pressure Microcatheter for clinical decision making would be non-inferior to pressure wire-based strategy After determining the presence of a coronary artery disease/ stabilized acute coronary syndrome, patients will be randomized to use a pressure microcatheter (investigational device) or a pressure wire (comparator) to guide and optimize percutaneous coronary intervention (PCI). Patients will be followed up in hospital at 12 months and yearly until five years.