Percutaneous coronary intervention (PCI) is a standard treatment strategy for coronary artery disease (CAD). With the presence of myocardial ischemia, PCI reduces the risks of death, myocardial infarction (MI), and revascularization compared to medical therapy. However, the risk of future clinical events remains high, and about 10% of patients experienced further cardiovascular events after PCI. Several factors are associated with these poor outcomes. Well-known patient-related risk factors are diabetes mellitus, chronic kidney disease, left ventricular dysfunction, previous MI, and presentation with acute coronary syndrome. Procedure-related factors, such as stent under expansion, malposition, edge dissection, the number of the used stent, and total stent length, are also related to poor prognosis after PCI. Recent studies reported that fractional flow reserve (FFR) after coronary stenting, or post-PCI FFR, was associated with future clinical outcomes after PCI, and low post-PCI FFR value was associated with procedural factors. However, optimal cut-off values of post-PCI FFR ranged widely, from 0.86 to 0.96, and some studies reported the limited prognostic value of post-PCI FFR. This might result from differences in study populations, the definition of outcomes, type of stent used, and distribution of included vessels among previous studies. Previously, the investigators incorporated previous data into the International Post-PCI FFR registry and demonstrated the prognostic value of post-PCI FFR using the machine learning technique. However, the results were based on the two years follow-up of patients after PCI, and the prognostic value of post-PCI FFR in long-term outcomes is still uncertain. Therefore, the investigators planned to extend the International Post-PCI FFR registry to define the long-term prognostic implication of post-PCI FFR.

The investigators planned to extend the International Post-PCI FFR registry (NCT04684043) to explore the long-term prognostic value of post-PCI FFR. The International Post-PCI FFR registry (NCT04684043) already included the 2,200 patients who underwent PCI and measured post-PCI FFR between June 2011 and May 2018. As the clinical, angiographic, and physiologic data are already collected in the International Post PCI FFR registry, the investigators will further collect the most recent clinical outcome data until 2021.5 and incorporate them into the International Post-PCI FFR Extended registry. As the current study will evaluate clinical outcomes at 5 years, 2,128 patients who underwent PCI and measured post-PCI FFR between June 2011 and Nov 2016 will be included and studied. The investigators will request further clinical outcome data from 10 hospitals that provided the data for the International Post-PCI FFR registry before.

A standardized form of a spreadsheet, including standardized definitions of variables, was used to collect the individual patient data from the principal investigators of each qualified registry. Patient clinical, angiographic, and physiologic data at the time of index PCI were recorded and already collected at Seoul National University Hospital. As clinical outcome data of 2 years of follow-up after index PCI are already collected in the International Post-PCI FFR registry (NCT04684043), clinical outcome data after 2 years of index PCI will be collected by medical records until 2021.5 of each hospital. All submitted data were double-checked by a central monitoring team in Seoul National University Hospital. All patients' identifying numbers are anonymized as "Subject_No" and the investigators will request the patients' clinical outcome data using these anonymized identifying numbers of the patients. Also, the investigators will share collected data with collaborators, using these numbers.

Inclusion Criteria:

- Patients who underwent PCI and post-PCI FFR measurements after angiographically successful stent implantation (residual stenosis < 20% by visual estimation)

Exclusion Criteria:

• Post-PCI TIMI (The Thrombolysis In Myocardial Infarction) flow of < 3
• Depressed left ventricular systolic function (ejection fraction < 30%)
• Culprit lesion for the acute coronary syndrome
• Graft vessel
• Collateral feeder
• In-stent stenosis
• Primary myocardial or valvular heart disease
• Patients with life expectancy < 2 years.

Patients who were diagnosed as obstructive coronary artery disease and treated by DES and measured post PCI FFR after PCI.

This issue has to be discussed with collaborators.