Despite the evidence, most stable patients continue to be managed based on coronary angiography and, worse, often without a prior non-invasive functional study.

With the introduction of the FFR, we left the “anatomical” era for the “functional” era in the catheterization room, which has been proven to improve patients prognosis and, as if that were not enough, is saving costs.

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Despite all of the above, the FFR continues to be used occasionally worldwide, and perhaps, one of the reasons, it is somewhat cumbersome to use it, and it is necessary to invest time in this.

As an alternative to FFR, the index measured in the free wave period (instantaneous wave-free ratio, iFR) emerged, which has the advantage of not needing hyperemia, so we save adenosine (both in cost and in symptoms) and make functional assessment faster and easier.

The objective of this work was to perform a meta-analysis of all the works that compared the FFR with the iFR to know if we can really change from gold standard to functional assessment.

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A total of 23 studies with 6381 stenoses were included, with a first meta-analysis of all the studies to explore the correlation between both indices. Results showed that this correlation was very good (0.798, CI 95% 0.78 to 0.82, p<0.001). Additionally, the diagnostic performance of iFR was evaluated to identify coronary lesions with positive FFR. This, like correlation, was also very good with an area under the curve of 0.88 (p <0.001).

Conclusion

The present meta-analysis shows that iFR correlates significantly with FFR and shows a very good diagnostic accuracy to identify lesions with positive FFR. Finally, the iFR and the FFR showed that they have a similar diagnostic efficacy to detect ischemic lesions. This was observed when compared to a third parameter with coronary flow measured by Doppler.

Editorial Comment

The analysis confirms the good correlation between FFR and iFR, although this is not perfect and there will always be some degree of divergence; which initially worried. However, studies using a third validated method to detect ischemia such as positron emission tomography and coronary flow measurement with Doppler, showed that when there was divergence between both indices, half of the time the third method coincided with the FFR and the other half with the iFR.

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This would make the hybrid evaluation that we suggested in the early days of the iFR, unnecessary where the intermediate values of the same (0.86 to 0.94) should be confirmed with FFR and adenosine.

Additionally, recent studies such as DEFINE-Flair and iFR-SWEDEHEART confirmed non-inferiority in terms of clinical events when using iFR versus FFR.

Original Title: Diagnostic Performance of the Instantaneous Wave-Free Ratio Comparison With Fractional Flow Reserve.

Reference: Salvatore De Rosa et al. Circ Cardiovasc Interv. 2018 Jan; 11(1):e004613.

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