Detecting lesion-specific ischemia in patients with coronary artery disease with computed tomography fractional flow reserve measured at different sites
Authors: Cai Zhaoxi , Yu Taihui , Yang Zehong , Hu Huijun , Lin Yongqing , Zhang Haifeng , Chen Meiwei , Shi Guangzi , Shen Jun 
Published: January 2023

Objectives
Selection of an appropriate site along the coronary artery tree is vital for measuring computed tomography fractional flow reserve (FFRCT) in patients with coronary artery diseases (CAD). The purpose of this study was to evaluate the performance of FFRCT measured at different sites distal to the target lesion in detecting lesion-specific ischemia in patients with CAD as compared with fractional flow reserve (FFR) measured with invasive coronary angiography (ICA).
Methods
In this retrospective study, 52 patients suspected of having CAD were enrolled between March 2017 to December 2021. All patients underwent coronary computed tomography angiography (CCTA) and ICA together with FFR measurement within 90 days. Vessels with 30%-90% diameter stenosis as determined by ICA were referred to invasive FFR evaluation, which was performed 2–3 cm distal to the stenosis under the condition of hyperemia. For each vessel with 30–90% diameter stenosis, if only one stenosis was present, this stenosis was selected as the target lesion; if serial stenoses were present, the stenosis most distal to the vessel end was chosen as the target lesion. FFRCT was measured at four sites: 1cm, 2 cm, and 3 cm distal to the lower border of the target lesion (FFRCT-1cm, FFRCT-2cm, FFRCT-3cm), and the lowest FFRCT at the distal vessel tip (FFRCT-lowest). Pearson's correlation analysis and Bland–Altman plots were used to assess the correlation and difference between invasive FFR and FFRCT. The performances of significant obstruction stenosis (diameter stenosis ≥ 50%) at CCTA and FFRCT measured at the four different sites in diagnosing lesion-specific ischemia were evaluated by receiver-operating characteristic (ROC) curves using invasive FFR as the reference standard. The areas under ROC curves (AUCs) of CCTA, FFRCT measured at the different sites were compared by the DeLong test.
Results
A total of 72 coronary arteries in 52 patients were included for analysis. Twenty-five vessels (34.7%) had lesion-specific ischemia detected by invasive FFR. Good correlation was found between invasive FFR and FFRCT-2cm and FFRCT-3cm (r = 0.80, 95% CI, 0.70 to 0.87, p < 0.001; r = 0.82, 95% CI, 0.72 to 0.88, p < 0.001). Moderate correlation was found between invasive FFR and FFRCT-1cm and FFRCT-lowest (r = 0.77, 95% CI, 0.65 to 0.85, p < 0.001; r = 0.78, 95% CI, 0.67 to 0.86, p < 0.001). Bland–Altman plots revealed a mild difference between invasive FFR and the four FFRCT (invasive FFR vs. FFRCT-1cm, mean difference − 0.0158, 95% limits of agreement: -0.1475 to 0.1159; invasive FFR vs. FFRCT-2cm, mean difference 0.0001, 95% limits of agreement: -0.1222 to 0.1220; invasive FFR vs. FFRCT-3cm, mean difference 0.0117, 95% limits of agreement: -0.1085 to 0.1318; and invasive FFR vs. FFRCT-lowest, mean difference 0.0343, 95% limits of agreement: -0.1033 to 0.1720). AUCs of CCTA, FFRCT-1cm, FFRCT-2cm, FFRCT-3cm, and FFRCT-lowest in detecting lesion-specific ischemia were 0.578 (95% CI, 0.443 to 0.713), 0.768 (95% CI, 0.640 to 0.896), 0.857 (95% CI, 0.754 to 0.961), 0.856 (95% CI, 0.756 to 0.957) and 0.770 (95% CI, 0.657 to 0.882), respectively. All FFRCT had a higher AUC than CCTA (all p < 0.05), FFRCT-2cm achieved the highest AUC at 0.857. The AUCs of FFRCT-2cm and FFRCT-3cm were comparable (p > 0.05).
Conclusions
FFRCT measured at 2 cm distal to the lower border of the target lesion is the optimal measurement site for identifying lesion-specific ischemia in patients with CAD.