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 the acute coronary syndrome. Procedure-related factors, such as stent underexpension, malapposition, 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 study 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.

To establish the clinical relevance of post-PCI FFR and to evaluate the useful cut-off value of post-PCI FFR in daily practice, investigators planned to incorporate all previous evidence of post-PCI FFR by collaboration with international researchers.

This study population was incorporated from studies which were already published. Investigators will incorporate all known registries to the POST-PCI FLOW registry by requesting data from principal investigator of each registry.

Investigators will perform systemic review of the previous published data and an updated patient-level meta-analysis of studies, including the most recent publications. PubMed, EMBASE, Cochrane Central Register of Controlled Trials, the United States National Institutes of Health registry of clinical trials, and relevant websites were searched for pertinent published studies. The electronic search strategy was complemented by manual examination of references cited by included articles, recent reviews, editorials, and meta-analyses. No restrictions were imposed on language, study period, or sample size. Searching key words included 'post', 'after', 'PCI', 'Percutaneous coronary intervention', 'coronary stenting', 'stenting', 'stent', 'stent implantation', 'FFR', and 'fractional flow reserve'.

Articles were included when they met the following prespecified criteria: (1) included the patients who underwent PCI with drug-eluting stent (DES); (2) post-PCI FFR was measured after DES implantation; (3) pre-PCI FFR measurement was not mandatory for article inclusion; (4) patients were followed up at least 6 months; (5) clinical outcomes, including all-cause death, cardiac death, target vessel myocardial infarction (TVMI) or target vessel revascularization (TVR), were clearly reported; (6) randomized controlled trials or non-randomized prospective or retrospective registries were included. Two independent investigators screened titles and abstracts, identified duplicated studies, performed full-article reviews, and determined the studies' inclusion. The third investigator supervised the searching process and adjudicated all the disagreements.

• 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.