Fractional flow reserve from coronary CT angiography compared with quantitative flow ratio in complex CAD

Background: Diagnostic concordance among Fractional Flow Reserve derived from computed tomography (FFRCT), and the Quantitative flow ratio (QFR) and Murray's Law-based QFR (μFR) derived from invasive coronary angiography (ICA) is implicitly assumed. Methods: Coronary CT angiography (CCTA) and ICA were analyzed in a central imaging core lab in this post-hoc imaging sub-study of the FASTTRACK CABG trial that enrolled 114 patients with de-novo three-vessel and/or left-main coronary artery disease. FFRCT, QFR, and μFR were analyzed at corresponding bifurcation points on CCTA and ICA, and virtual pullback pressure gradient index (PPGi) and FFR derivatives (dFFR/ds) were assessed to patho-physiologically categorize the lesion phenotype into diffuse or focal. Results: In 199 vessels, mean distal estimates of FFRCT (0.70), QFR (0.71), and μFR (0.69) were similar (p ​= ​0.127). QFR was significantly higher than FFRCT (p ​< ​0.01) and μFR (p ​< ​0.01) in the main branches of the two most proximal bifurcations. Concordance between FFRCT and QFR, and FFRCT and μFR was 76.3 ​% (kappa ​= ​0.451) and 80.3 ​% (kappa ​= ​0.544), respectively, when using a cut-off of ≤0.80. Concordance in the pathophysiological lesion phenotype (diffuse or focal) as derived from virtual PPGi was poor between FFRCT vs QFR (k ​= ​0.04) and FFRCT vs μFR (k ​= ​0.16). QFR (20.9 ​%) tended to identify focal lesions more frequently than FFRCT (13.4 ​%) and μFR (7.5 ​%). Conclusions: In the two most proximal bifurcations, QFR values were higher than FFRCT and μFR, resulting in lesion severity being underestimated, which may impact revascularization decisions. The pathophysiological phenotype classification was poorly correlated among FFRCT, QFR, and μFR. Trial registration number: NCT04142021.