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. 2020 Aug 11;28(Suppl 1):99–107. doi: 10.1007/s12471-020-01461-7

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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 licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence 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 licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — Instantaneous wave-free ratio. Instantaneous wave-free ratio (iFR) is defined as the mean distal coronary pressure (Pd) to mean aortic pressure (Pa) ratio over the wave-free period (WFP). The WFP is defined as starting 25% into cardiac diastole, and ending 5 ms before the end of diastole as illustrated