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

To evaluate agreement between instantaneous wave free ratio (iFR) and fractional flow reserve (FFR) for the functional assessment of nonculprit coronary stenoses at staged follow-up after ST-segment elevation myocardial infarction (STEMI). 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.