AIMS:To analyse the relationship between stent expansion criteria using optical coherence tomography (OCT) analysis and the final PCI functional result. METHODS AND RESULTS:This post-hoc analysis of the DOCTORS study included non-ST elevation segment ACS patients undergoing OCT-guided PCI. The procedure functional result was assessed by the measurement of fractional flow reserve (FFR). Stent expansion was assessed on OCT runs according to the DOCTORS criteria and ILUMIEN-III criteria. The study included N=116 patients (Age: 60.8±11.5 years/ male gender:71%). The final expansion was considered optimal in 10%, acceptable in 9% and unacceptable in 81% of the stents according to ILUMIEN-III criteria, although being successful in 70% of the patients according to the DOCTORS criteria. Hypertension and larger proximal reference segment dimension were independent predictors of inadequate device ILUMIEN-III expansion. FFR values were respectively 0.93[0.91-0.95] vs. 0.95[0.92-0.97] in patients with optimal+ acceptable vs. unacceptable ILUMIEN-III expansion (p=0.22), 0.94[0.91-0.97] vs. 0.95 [0.93-0.97] in patients with optimal vs. non-optimal DOCTORS expansion (p=0.23) and 0.95[0.92-0.97] vs. 0.92[0.90-0.95]in patients with minimal stent area ³4.5 mm2 vs. <4.5 mm2 (p=0.03). CONCLUSIONS:In this selected population, no relationship was observed between optimal stent expansion according to ILUMIEN-III or DOCTORS OCT criteria and final post-PCI FFR values.