Previous trials have demonstrated that the use of physiological assessment of stenosis severity using fractional flow reserve (FFR) is superior to angiographic assessment in percutaneous coronary intervention (PCI) and improves clinical outcome. Despite the clinical utility, FFR is used only in 10-15% of patients today. The main reasons for the low adoption rate of FFR are the prolonged procedural time, Adenosine related discomfort and cost associated with Adenosine.

Instantaneous Wave-Free ratio (iFR®) is a novel method to assess coronary lesions for functional significance. The main benefits of the method compared to FFR are that the measurement is instantaneous and does not require Adenosine infusion. Thus, the patient does not experience any discomfort from the measurement and procedural time could be shortened compared to when using FFR. This could potentially increase the adoption rate of physiologic assessment of coronary lesions.

The aim of this trial is to compare the clinical outcome of patients assessed by iFR® with patients assessed by FFR.

Furthermore, the trial will be conducted as a registry based randomized clinical trial (RRCT) which is a novel strategy to conduct clinical trials. The randomization will occur online in the Swedish angiography and angioplasty registry (SWEDEHEART) using a web based platform.

Inclusion Criteria:

• Patients with suspected stable angina pectoris or unstable angina pectoris/non-ST-segment elevation myocardial infarction (NSTEMI) who are scheduled to undergo coronary angiography, and who has an indication for physiology guided assessment of coronary lesions (usually 30-80% stenosis grade). In patients with suspected stable angina pectoris, any lesion may be assessed. In patients with unstable angina pectoris/NSTEMI, only the non-culprit lesion may be assessed.

Exclusion Criteria:

• Inability to provide informed consent
• Age below 18 years
• Previous randomization in the iFR-SWEDEHEART trial
• Known terminal disease with a life expectancy of less than one year.
• In patients with multi-vessel disease and other indication than stable angina pectoris, difficulty in assessing which the culprit lesion is.
• Patient with unstable hemodynamics (Killip class III-IV)
• Inability to tolerate Adenosine
• Previous Coronary artery bypass graft (CABG) with patent grafts to the interrogated vessel.
• Heavily calcified or tortuous vessel where inability to cross the lesion with a pressure wire is expected.