Fig. 4

Relation between pre-PCI PPG index and odds ratio of optimal post-PCI QFR. Cubic spline curve showing the odds ratio of optimal post-PCI QFR (vertical axis) according to the pre-PCI QFR PPG index (horizontal axis). Abbreviations: PCI, percutaneous coronary intervention; QFR, quantitative flow ratio; PPG, pullback pressure curve gradient.