OBJECTIVES The authors investigated 2-year clinical outcomes according to fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) values in deferred lesions.

BACKGROUND Invasive physiological indices such as FFR or iFR are used in clinical practice to select ischemia-causing stenosis and to guide the treatment strategy for patients with coronary artery disease.

METHODS From the 3V FFR-FRIENDS (3-Vessel Fractional Flow Reserve for the Assessment of Total Stenosis Burden and Its Clinical Impact in Patients With Coronary Artery Disease) study, 821 deferred lesions (n = 374) with both FFR and iFR available were included in this study. The primary outcome was major adverse cardiac events (MACE) (a composite of cardiac death, myocardial infarction, and ischemia-driven revascularization) at 2 years. The lesions were classified according to FFR and iFR cutpoints into concordant normal (Group 1: FFR >0.80 and iFR >0.89), high FFR and low iFR (Group 2: FFR >0.80 and iFR ≤0.89), low FFR and high iFR (Group 3: FFR ≤0.80 and iFR >0.89), and concordant abnormal (Group 4: FFR ≤0.80 and iFR ≤0.89).

RESULTS Deferred lesions with low FFR (≤0.80) or low iFR (≤0.89) showed significantly higher rates of 2-year MACE, compared with high FFR (>0.80) or high iFR (>0.89), respectively (7.2% in low FFR vs. 2.4% in high FFR; p < 0.001; 8.1% in low iFR vs. 2.4% in high iFR; p < 0.001). Both FFR and iFR showed significant association with occurrence of MACE as continuous values (hazard ratio [HR] of FFR: 0.570, 95% confidence interval [CI]: 0.337 to 0.963; p < 0.001; HR of iFR: 0.350, 95% CI: 0.217 to 0.567; p < 0.001). When comparing the discriminant ability between FFR and iFR, the c-index was comparable between FFR and iFR (c-index 0.677 vs. 0.685; p = 0.857). Among 4 groups classified according to FFR and iFR levels, only Group 4 with concordant abnormal results showed significantly higher risk of MACE, compared with group 1 (HR: 7.708, 95% CI: 2.621 to 22.667; p < 0.001).

CONCLUSIONS Both FFR and iFR showed significant association with future risk of MACE in deferred lesions. The discordant results between FFR and iFR were not associated with the increased risk of MACE. The risk of MACE was significantly increased only in lesions with abnormal results of both FFR and iFR.