Comparison of instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR)

BACKGROUND:

The instantaneous wave-free ratio (iFR) is a new adenosine-independent index of coronary stenosis severity. We prospectively compared real-time iFR and fractional flow reserve (FFR) measurements.

METHODS AND RESULTS:

iFR and FFR were measured in 122 angiographically borderline coronary narrowings in 104 patients from 2 medical centers. Cutoff for FFR was 0.80 and for iFR 0.89. Repeated iFR measurements were technically simple, showed excellent agreement [rs=0.99; p<0.0001], and the mean difference between consecutive iFR values was 0.01 (limits of agreement: -0.019, 0.026). Mean iFR showed a significant correlation with FFR [rs=0.81; p<0.0001]. Receiver-operating characteristic analysis identified in our group of patients, an optimal iFR cut-off value of 0.87 for categorization based on an FFR cut-off value 0.8.

We compared two different iFR-based diagnostic strategies (iFR-only and hybrid iFR-FFR) with standard FFR: The iFR-only strategy showed good classification agreement (92%) with standard FFR [60/65 cases]. Use of the hybrid iFR-FFR strategy, assessing lesions in an iFR-gray zone of 0.86-0.93 by FFR, improved classification accuracy to 94%. In 95/122 77.9% there was agreement between FFR and iFR, and diagnosis would have been established without adenosine-induced hyperemia.

CONCLUSIONS:

Real-time iFR measurements are easily performed, have excellent diagnostic performance and confirm available off-line core laboratory data. The excellent agreement between repeated iFR measurements demonstrates the reliability of single measurements. Combining iFR with FFR in a hybrid strategy enhances diagnostic accuracy, exposing fewer patients to adenosine. Overall, iFR is a promising method, but still requires prospective clinical endpoint trial evaluation.