In-stent fractional flow reserve variations and related optical coherence tomography findings: the FFR–OCT co-registration study

We sought to assess in-stent variations in fractional flow reserve (FFR) in patients with previous percutaneous coronary intervention (PCI) and to associate any drop in FFR with findings by optical coherence tomography (OCT) imaging. Suboptimal post-PCI FFR values were previously associated with poor outcomes. It is not known to which extent in-stent pressure loss contributes to reduced FFR. In this single-arm observational study, 26 patients who previously underwent PCI with drug-eluting stent or scaffold implantation were enrolled. Motorized FFR pullback during continuous intravenous adenosine infusion and OCT assessments was performed. Post-PCI FFR < 0.94 was defined as suboptimal. At a median of 63 days after PCI (interquartile range: 59–64 days), 18 out of 26 patients (72%) had suboptimal FFR. The in-stent drop in FFR was significantly higher in patients with suboptimal FFR vs. patients with optimal FFR (0.08 ± 0.07 vs. 0.01 ± 0.02, p < 0.001). Receiver operating characteristic curve analysis showed that an in-stent FFR variation of > 0.03 was associated with suboptimal FFR. In patients with suboptimal FFR, the OCT analyses revealed higher mean neointimal area (respectively: 1.06 ± 0.80 vs. 0.51 ± 0.23 mm²; p = 0.018) and higher neointimal thickness of covered struts (respectively 0.11 ± 0.07 vs. 0.06 ± 0.01 mm; p = 0.021). Suboptimal FFR values following stent-implantation are mainly caused by significant in-stent pressure loss during hyperemia. This finding is associated to a larger neointimal proliferation.