Comparison of instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR) — First real world experience

Abstract Background The instantaneous wave-free ratio (iFR) is a new adenosine-independent index of coronary stenosis severity. Most published data have been based on off-line analyses of pressure recordings in a core laboratory. We prospectively compared real-time iFR and fractional flow reserve (FFR) measurements. Methods and results iFR and FFR were measured in 151 coronary stenoses in 108 patients. Repeated iFR measurements were technically simple, showed excellent agreement [rs = 0.99; p < 0.0001], and the mean difference between consecutive iFR values was 0.0035 (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 an optimal iFR cut-off value of 0.896 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 (83.4%) with standard FFR. 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 94.7%, and diagnosis would have been established in 61% of patients without adenosine-induced hyperemia. Notably, both iFR and FFR values were significantly higher in the posterior coronary vessels. 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.