Background Post-percutaneous coronary intervention (PCI) fractional flow reserve (FFR)
is an established method to evaluate the functional result of angiographically successful
PCI; however, it is rarely measured. Quantitative flow ratio (QFR) is shown to be
correlated with FFR before PCI. In this observational study we sought to evaluate
the correlation and relative prognostic value of post-PCI QFR compared with post-PCI
FFR.Methods and Results We analyzed the outcome of all patients who underwent FFR-guided
PCI with post-PCI FFR measurement. Post-PCI QFR was calculated offline, blinded to
the value of post-PCI FFR and the clinical outcome. The primary end point was target-vessel
failure (TVF) defined as the composite of cardiovascular death, target-vessel-related
nonfatal myocardial infarction, and target-vessel repeat revascularization. The secondary
end point was the composite of cardiovascular death and myocardial infarction. Median
follow-up was 50 months. QFR calculation was unsuccessful in 15.6% of the vessels;
thus, 422 vessels of 365 patients were included in the analysis. Post-PCI QFR systematically
overestimated post-PCI FFR with a mean bias of +0.052, and their correlation was poor
(Pearson's r=0.424). Post-PCI FFR was an independent predictor of TVF and cardiovascular
death/myocardial infarction. Post-PCI QFR was associated with TVF, but was not an
independent predictor of either TVF or cardiovascular death/myocardial infarction.
The optimal cutoff of post-PCI FFR to predict TVF was 0.83, whereas no optimal cutoff
of post-PCI QFR could be found.Conclusions Post-PCI QFR has a poor correlation with
and overestimates post-PCI FFR. Whereas post-PCI FFR is an independent predictor of
clinical outcome, post-PCI QFR is not.
