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The ‘wave-free period’ is not always ‘wave-free’: an explanation for discordance between Instantaneous Wave-Free Ratio and Fractional Flow Reserve with increasing stenosis severity

Research output: Contribution to journalArticle

Mark T. Mills, Bhavik Modi, Sadman Chowdhury, Haseeb Rahman, Matt Ryan, Howard Ellis, Divaka Perera

Original languageEnglish
JournalCardiology Journal
Accepted/In press30 May 2020

King's Authors

Abstract

Background FFR and iFR are the most commonly used tests to determine whether coronary lesions should be treated by revascularization. Although considered prognostically equivalent, lesions are discordantly classified in about 25% of cases. We characterised the ‘wave-free period’ (WFP) for coronary stenoses of varying severity and assessed whether a true WFP affects concordance of Instantaneous wave-free ratio (iFR) and Fractional flow reserve (FFR). Methods Patients referred for coronary angiography who had undergone simultaneous intracoronary pressure and flow velocity assessments were retrospectively included. Hyperemic stenosis resistance (hSR) and microvascular resistance (MR) were calculated. The WFP (final 75% of diastole minus the last 5ms) was examined using wave intensity analysis and the percentage of the WFP that was truly ‘wave-free’ calculated. Thresholds for lesion significance were: FFR≤0.80, iFR≤0.89 and hSR>0.8 mmHg/cm/s; significant lesions denoted “+”, non-significant lesions “–”. Results 143 patients aged 62.3±11.2 were enrolled (143 vessels). 20.3% were discordantly classified. In FFR–/iFR– concordance, no waves were detected in the WFP in 81% of cases; this contrasted with 43% in FFR+/iFR– discordance, 40% in FFR–/iFR+ discordance, and 27% in FFR+/iFR+ concordance (P<0.001 across groups). The percentage of the WFP that was truly ‘wave-free’ was lower in hSR+ vessels compared to hSR– vessels 1 (80.2±20.36% vs. 94.2±10.42%, P<0.001). MR during the WFP was higher than MR during pharmacological hyperemia (4.45±2.37 mmHg.cm-1.s-1 vs. 3.07±1.78 mmHg.cm-1.s-1, P<0.001). Conclusion The likelihood that the WFP is not ‘wave-free’ increases with physiological severity of the CAD and explains some of the discordance between FFR and iFR.

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