Objectives Fractional flow reserve (FFR) has been suggested to have value in acute coronary syndromes (ACSs). The clinical and prognostic value of ischaemia reduction assessed by post-percutaneous coronary intervention (PCI) FFR has not been studied in this population.

Methods Consecutive stable ischaemic heart disease (SIHD) (N=390) and patients with ACS (N=189) who had pre-PCI FFR and post-PCI FFR were followed for 2.4±1.5 years. Primary endpoint was major adverse cardiac events (MACE) (composite of myocardial infarction, target vessel revascularisation and death).

Results In patients with ACS, PCI led to significant improvement in FFR from 0.62±0.15 to post-PCI FFR 0.88±0.08 (p<0.0001). Post-PCI FFR identified 29 patients (15%) who had persistently low FFR<0.80 (0.75±0.06) despite angiographically optimal results prompting subsequent interventions improving repeat FFR (0.85±0.06; p<0.0001). The difference in MACE events between patients with ACS and patients with SIHD varied according to the post-PCI FFR value (interaction p=0.044). Receiver operator curve analysis identified a final FFR cut-off of ≤0.91 as having the best predictive accuracy for MACE in the ACS study population (30% vs 19%; p=0.03). Patients with ACS achieving final FFR of >0.91 had similar outcomes compared with patients who had SIHD (19% vs 16%; p=0.51). However, in patients with final FFR of ≤0.91 there was increased MACE versus patients with SIHD (30% vs 16%; p<0.01).

Conclusions Post-PCI FFR is valuable in assessing the functional outcome of PCI in patients with ACS. Use of post-PCI FFR in patients with ACS allows for functional optimisation of PCI results and is predictive of long-term outcomes in patients with ACS.