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. 2020 Feb 24;17(7):427–450. doi: 10.1038/s41569-020-0341-8

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 8 — a | Representation of the ratio of resting distal coronary pressure (P_d) to aortic pressure (P_a), instantaneous wave-free ratio (iFR), fractional flow reserve (FFR) and coronary flow reserve (CFR) calculation from invasively assessed coronary pressure or flow measurement. b | Agreement between coronary pressure (FFR or iFR) and CFR measurement. Discordance between FFR and CFR occurs in 30–40% of individuals, whereas better agreement can be observed between iFR and CFR. c | Interpretation of combined FFR and CFR measurement and its effect on clinical outcome¹⁹³. Four main quadrants can be identified by the clinical cut-off values for FFR and CFR, indicated by the dashed lines. Patients in the upper right area (blue) have normal FFR and CFR; patients in the lower left area (red) have abnormal FFR and CFR; patients in the upper left area (orange) have abnormal FFR and normal CFR; and patients in the lower right area (green) have normal FFR and abnormal CFR, which indicates predominant microvascular involvement or diffuse coronary artery disease. Patients in the small dark green region in the lower right have an FFR close to 1 and an abnormal CFR, indicating sole involvement of the coronary microvasculature. The prognostic value of FFR and CFR in terms of major adverse cardiovascular events (MACE) is shown on the right. Part c adapted with permission from ref.¹⁹³, van de Hoef, T. P. et al. Physiological basis and long-term clinical outcome of discordance between fractional flow reserve and coronary flow velocity reserve in coronary stenoses of intermediate severity. Circ. Cardiovasc. Interv. 7(3), 301–311 (https://www.ahajournals.org/journal/circinterventions).