Caution! You're approaching a gray zone: FFR outcomes and the role of CFR and IMR.

This study demonstrates that compared with low- fractional flow reserve (FFR) lesions (<0.75), those in the gray-zone FFR (0.75-0.80) are less likely to have improvement or more likely to have impairment in flow after percutaneous coronary intervention. The findings suggest index of microcirculatory resistance measurement may help identify lesions in the FFR gray zone that are most likely to improve. The study reinforces that FFR measurements represent a continuum of ischemic values and that a single dichotomous threshold oversimplifies the answer to whether a lesion should be revascularized.