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. However, data on the validity of QFR in setting of ACS is scarce. Therefore, the aim of this study was to assess the feasibility and diagnostic reliability of serial QFR-measurements in non-culprit vessels of patients at ACS- and at staged-PCI procedures. 

Methods and results: A total of 321 patients with ACS (50.2% STE-ACS and 49.8% NSTE-ACS) with multivessel-disease, who underwent primary PCI and were planned for further staged PCI-procedure of at least one non-culprit lesion >70% diameter stenosis by visual estimation were enrolled in the entire analysis. Within this patient cohort 3D-QCA and QFR analyses of 513 non-culprit vessels were post-hoc serial performed by certified investigators using a validated software (QAngio XA/3D, Medis, Leiden, the Netherlands). 

The median time interval was 49 [42-58] days between index and staged PCI. Contrast-flow vessel QFR in non-culprit coronary arteries at time of index ACS event and staged procedure showed a good correlation (r=0.94 (95% CI 0.93-0.95), p<0.001) and agreement (mean difference -0.008, 95% CI -0.013-0.003). Importantly, QFR as assessed at index procedure had  sensitivity of 95.02%, specificity of 93.59%, PPV of 90.52%, NPV of 96.69%, and diagnostic accuracy of 94.15% in prediction of contrast-flow vessel QFR ≤0.80 at the time of staged procedure and therefore to detect hemodynamic relevance of non-culprit lesions.

Conclusions: The present study confirms for the first time the feasibility and diagnostic accuracy of QFR assessment of non-culprit coronary arteries during ACS. These results support QFR as valuable tool in patients with ACS to detect further hemodynamic relevant lesions with excellent diagnostic performance and therefore to guide further revascularisation therapy.