LAUSR

Since the beginning of fractional flow reserve (FFR) there has been a concern for its accuracy in acute coronary syndromes (ACS). For the culprit artery in both ST‐elevation myocardial infarction (STEMI) and non‐ST‐elevation myocardioal infarction (NSTEMI), there is little practical use for physiologic measurements since the active thrombotic lesion may be transiently patent (with negative FFR) while the myocardial bed will be impaired to some unknown degree limiting hyperemia and true FFR compared to that in the recuperative phase. Stenting is therefore appropriate in the ACS culprit vessel without further ado. In contrast, in the nonculprit artery in an acute STEMI, FFR has been shown to be largely accurate with the caveat that microvascular flow impairment in the measurement bed may slightly but falsely elevate the apparent FFR (Figure 1). Therefore, in this setting, a low FFR would indicate a true hemodynamically significant lesion, but a normal or negative FFR may not be definitive. Ntalianis et al. among others have demonstrated that FFR for nonculprit vessels changes only modestly in the postinfarction period. The question of FFR reliability extends to a lesser degree for NSTEMI patients but additional discussions invariably arise. The fractional flow reserve versus angiography in guiding management to optimize outcomes in non‐ST‐elevation myocardial infarction (FAMOUS‐NSTEMI) cardiac magnetic resonance substudy showed an excellent accuracy of FFR < 0.80 for predicting perfusion defects on cardiac magnetic resonance imaging, while the main study results affirmed the value of FFR in NSTEMI patients. As we begin the transition from wire‐based FFR (FFRinvasive) to angiographically derived FFR (FFRangio, CathWorks), Skalidisa et al. 3