Physiological Disease Pattern as Assessed by Pull Back Pressure Gradient Index in Vessels With FFR/iFR Discordance

Background: Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are discordant in approximately 20% of cases, and it is unclear whether this is influenced by the physiological pattern of coronary artery disease (CAD). The pull back pressure gradient index (PPGi) can objectively characterize the physiological pattern of CADs. Objectives: The aim of this study was to evaluate whether PPGi differed in discordant groups (FFR+/iFR− vs FFR−/iFR+). Methods: The study enrolled 355 patients (390 vessels) with chronic coronary syndrome who had ≥1 epicardial coronary artery lesion with 40% to 90% diameter stenosis by visual assessment on invasive coronary angiography and had analyzable FFR, iFR, and PPGi derived from quantitative flow ratio. Cutoffs for hemodynamic significance were FFR ≤0.80 and iFR ≤0.89. Vessels were classified as FFR+/iFR+ (n = 103 [26.4%]), FFR−/iFR+ (n = 27 [6.9%]), FFR+/iFR− (n = 38 [9.7%]), and FFR−/iFR− (n = 222 [57%]) groups. Results: Median FFR, iFR, and quantitative flow ratio were 0.84 (Q1-Q3: 0.77-0.90), 0.92 (Q1-Q3: 0.88-0.97), and 0.83 (Q1-Q3: 0.73-0.90), respectively. FFR disagreed with iFR in 16.7% of cases (65 of 390). The median PPGi was 0.75 (Q1-Q3: 0.67-0.85). The physiological pattern of CAD was classified according to the PPGi as predominantly physiologically focal (PPGi ≥0.75) in 209 of 390 vessels (53.6%) or diffuse (PPGi < 0.75) in 181 of 390 vessels (46.4%). The median PPGi was significantly lower in FFR−/iFR+ vs FFR+/iFR− vessels (0.65 [Q1-Q3: 0.60-0.69] vs 0.82 [Q1-Q3: 0.75-0.85]; P < 0.001). Predominantly physiologically focal disease was significantly associated with FFR+/iFR− (76.3% [29 of 38]), while predominantly physiologically diffuse disease was significantly associated with FFR−/iFR+ (96.3% [26 of 27] [P < 0.001] for pattern of CAD between FFR+/iFR− and FFR−/iFR+ groups). Conclusions: The physiological pattern of CAD is an important influencing factor in FFR/iFR discordance. (Radiographic Imaging Validation and Evaluation for Angio iFR [REVEAL iFR]; NCT03857503)