Discordance Between Fractional Flow Reserve and Coronary Flow Reserve: Insights From Intracoronary Imaging and Physiological Assessment

Abstract Objectives The aim of this study was to investigate the epicardial and microvascular substrates associated with discordances between fractional flow reserve (FFR) and coronary flow reserve (CFR) values. Background Discordances between FFR and CFR remain poorly characterized. Methods FFR, hyperemic stenosis resistance (HSR), and intravascular ultrasound were performed as indexes of epicardial function and CFR and hyperemic microvascular resistance (HMR) as measures of microvascular function in 94 patients with moderate coronary stenosis. Maximal plaque burden (PB max ), HSR, and HMR were calculated in 4 quadrants based on values of FFR ≤0.80 and CFR ≤2.0 as follows: concordant normal (preserved FFR and CFR), concordant abnormal (low FFR and CFR), discordant low FFR and preserved CFR, and discordant preserved FFR and low CFR. Results Sixty-four patients (68%) had concordant FFR and CFR findings, and 30 patients (32%) had discordant FFR and CFR. Compared with patients with preserved FFR and CFR, those with low FFR and CFR had higher PB max (p = 0.003), higher HSR (p  max and HSR but a trend toward higher HMR (p = 0.058) compared with patients with preserved CFR. Among patients with reduced FFR, those with preserved CFR had lower PB max (p = 0.004), a trend toward lower HSR (p = 0.065), and lower HMR (p = 0.03) compared with patients with reduced CFR. Furthermore, compared with patients with preserved FFR and low CFR, those with low FFR and preserved CFR had higher HSR (p = 0.022) but lower HMR (p = 0.003). Conclusions In patients with moderate coronary stenosis, preserved FFR and low CFR is associated with increased microvascular resistance, while low FFR and preserved CFR has modest epicardial stenosis and preserved microvascular function.