Fractional flow reserve and the index of microvascular resistance in patients with acute coronary syndromes

Aims: The aim of this article is to review what is currently known about fractional flow reserve (FFR) and related coronary physiological indices in patients with acute coronary syndrome (ACS) including non-ST-elevation (NSTEMI) and ST-elevation myocardial infarction (STEMI) with a view to making recommendations for daily practice. Methods and results: We explored all relevant publications to date including literature reviews, clinical trials and registries. We identified sufficient data on FFR in the setting of NSTEMI to confirm it to be a reliable and useful tool for lesion-level decision making with certain pitfalls as outlined below. There was limited published literature on FFR in STEMI. However, there is some evidence that, in patients who are stable after culprit lesion intervention, FFR may be of value for assessing the functional significance of non-culprit lesions. When measured in the culprit artery of patients with STEMI, the index of myocardial resistance (IMR) predicts long-term clinical outcomes. Conclusions: In patients with ACS, there is an increasing evidence base to support the role of FFR to guide revascularisation and of IMR to predict outcome.