Background: Several studies have demonstrated the feasibility and safety of hemodynamic assessment of non-culprit coronary arteries during acute coronary syndrome (ACS) using fractional flow reserve (FFR) measurements.Quantitative flow ratio (QFR) was recently introduced as fast FFR computation from invasive coronary angiography without the need for pressure wire or the induction of hyperemia and has been validated with good correlation and diagnostic performance to FFR in chronic coronary syndrome. The aim of this study was to define the prognostic role of angiography-based QFR in non-culprit and post-PCI culprit arteries of patients with ACS.

Methods: In a total of 900 patients with ACS, QFR analyses of non-culprit arteries (n=1400 vessels) and post-PCI culprit arteries (n=794 vessels) were post-hoc performed by certified investigators using validated software (QAngio XA/3D, Medis, Leiden, the Netherlands) and blinded to patients´ clinical outcome. Major adverse cardiovascular events (MACE) including all-cause mortality, myocardial infarction and ischemia-driven coronary revascularization within two years after ACS were assessed and adjudicated blinded to QFR results. 

Results: Out of the 900 patients with ACS (48.0% STE-ACS and 52.0% NSTE-ACS) 68.7% had male gender and median age was 68 years [58-77]. MACE within two years of follow-up after ACS occurred with rates of 7.4% associated to non-culprit arteries and 8.3% associated to culprit vessels, mainly driven by target vessel revascularization in both non-culprit and culprit arteries followed by myocardial infarctions in association with non-culprit arteries. An optimal QFR cut-off value of 0.85 for non-culprit arteries and 0.89 for post-PCI culprit arteries independently predicted MACE following an ACS event (non-culprit arteries: adjusted OR=5.61, 95% CI 2.79-11.30, p<0.001; and post-PCI culprit arteries: adjusted OR=6.00, 95% CI 3.35-10.76, <0.001).

Conclusions: The present study demonstrates for the first time a long-term prognostic value of QFR assessment in non-culprit as well as in post-PCI culprit arteries in a large all-comer ACS cohort. These results support QFR as a novel valuable tool for functional assessment also during ACS, which could improve risk prediction after ACS in future.