Comparison between instantaneous wave-free ratio versus morphometric assessments by intracoronary imaging

Anatomical measurements obtained by intracoronary imaging devices are reported to correlate significantly with fractional flow reserve (FFR). Instantaneous wave-free ratio (iFR) is a nonhyperemic index of stenosis severity with discordant reports regarding its accuracy in relation to FFR. There is no information on the correlation of iFR with measurements derived from intracoronary imaging devices. The purpose of this study was to assess the relationship among iFR, intravascular ultrasound (IVUS), and optical frequency domain imaging (OFDI) parameters. Eighty lesions in 72 patients who underwent elective angiography and had intermediate lesions were enrolled. All lesions were assessed by iFR, FFR, IVUS, and OFDI. iFR was ≤ 0.89 in 21 (26%) lesions and FFR was ≤ 0.80 in 41 (51%) lesions. iFR correlated significantly with both IVUS-derived minimum lumen area (MLA) (r = 0.375, p = 0.003) and OFDI-derived MLA (r = 0.357, p = 0.005). FFR also correlated significantly with both IVUS-derived MLA (r = 0.472, p < 0.001) and OFDI-derived MLA (r = 0.445, p < 0.001). Among the lesions with FFR ≤ 0.80, iFR > 0.89 (mismatch) was observed in 20 lesions. There was no lesion with iFR ≤ 0.89 (reverse mismatch) among the lesions with FFR > 0.80. The lesion location among three major coronary vessels was related with the discrepancy between iFR and FFR (p = 0.007). In conclusion, iFR and FFR showed a significant correlation with IVUS and OFDI measurements. The discrepancy of iFR and FFR was associated with the lesion locations.