Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are commonly used to assess physiological severity of angiographically intermediate stenosis. Both indexes quantify a pressure ratio as subrogate to measuring flow, which is much harder to do.

Discordance between FFR and iFR occurs in up to 20% of cases, which should not be a matter of concern, for in recent studies, such as the DEFINE-FLAIR (Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularization) and the iFR-SWEDEHEART (Evaluation of iFR vs FFR in Stable Angina or Acute Coronary Syndrome), more than 4500 patients have shown that iFR guided revascularization resulted non inferior to FFR guided revascularization as regards major adverse events at one year.

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This study sought to determine the coronary flow characteristics of angiographically intermediate stenosis classified as discordant by FFR and iFR.

The present study, called IDEAL (Iberian–Dutch–English Collaborators), is the largest study to physiologically asses stenosis with a combination of both pressure based indexes (FFR and iFR) and Doppler flow velocity that has been published so far.

The study compared flow velocity and coronary flow reserve (CFR) at baseline and under hyperemia in 5 groups, one group with unobstructed vessels (201 vessels, n=153), and 4 with angiographically intermediate stenosis: FFR+/iFR+ (108 vessels, n=91), FFR-/iFR+ (28 vessels, n=24), FFR+/iFR- (22 vessels, n=22), and FFR-/iFR- (208 vessels, n=154).

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Discordance between FFR and iFR was observed in 14% of patients (50 of 366). Baseline flow velocity was similar across all 5 groups, including, of course, the unobstructed vessel group.

In FFR+/iFR- discordants, hyperemic flow velocity and CFR resulted similar to the FFR-/iFR- groups and the unobstructed vessel group.

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In FFR-/iFR+ discordants, hyperemic flow velocity and CFR resulted similar to the FFR+/iFR+ group.

Conclusion

FFR/iFR discordance was explained by differences in hyperemic coronary flow velocity. Coronary flow resulted similar in unobstructed vessels and in intermediate stenosis when FFR turned out positive and iFR turned out negative for ischemia (FFR+/iFR-).

Editorial Comment

Measuring the effect of stenosis on coronary flow is technically more demanding and takes longer than simply measuring pressure gradient, which is why flow velocity and CFR have been replaced by FFR in the daily practice. Not only is FFR simpler tan CFR, but it is also supported by a large body of evidence (DEFER, FAME, etc.).

The results of this study suggest that when there is FFR/iFR discordance, the most revealing index (the one closest to hyperemic flow velocity) is iFR. This poses serious questions to FFR use in the daily practice, since iFR, compared against FFR, is even simpler, faster, less expensive, and causes less discomfort for patients, with less adenosine-driven symptoms.

Original title: Fractional Flow Reserve/Instantaneous Wave-Free Ratio Discordance in Angiographically Intermediate Coronary Stenoses. An Analysis Using Doppler-Derived Coronary Flow Measurements.

Reference: Christopher M. Cook et al. J Am Coll Cardiol Intv 2017;10:2514–24.

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