Simple visual estimation of coronary angiography is limited by several factors that can hinder the proper classification of coronary lesions. Fractional flow reserve (FFR) is the most widely used tool to perform a physiological evaluation of coronary stenoses. Compared to isolated angiography, FFR has been demonstrated to be more effective in selecting those lesions associated with myocardial ischemia and, accordingly, impaired outcomes. At the same time, deferring coronary intervention in those lesions that do not show ischemic FFR values has proven safe and not associated with adverse events. Despite a major randomized clinical trial (RCT) and several non-randomized studies showing that FFR-guided revascularization could be superior to isolated angiography in improving clinical outcomes, subsequent RCTs have reported conflicting results. In this review, we summarize the principles behind FFR and the data currently available in the literature, highlighting the main differences between randomized and non-randomized studies that investigated this topic.
