Agreement between nonculprit stenosis follow-up iFR and FFR after STEMI (iSTEMI substudy).

We measured iFR and FFR at staged follow-up in 112 STEMI patients with 146 nonculprit stenoses. Median interval between STEMI and follow-up was 16 (interquartile range 5-32) days. Agreement between iFR and FFR was 77% < 5 days after STEMI and 86% after ≥ 5 days (p = 0.19). Among cases with disagreement, the proportion of cases with hemodynamically significant iFR and non-significant FFR were different when assessed < 5 days (5 in 8, 63%) versus ≥ 5 days (3 in 15, 20%) after STEMI (p = 0.04). Overall classification agreement between iFR and FFR was comparable to that observed in stable patients. Time interval between STEMI and follow-up evaluation may impact agreement between iFR and FFR.