Fractional flow reserve in acute coronary syndromes and in stable ischemic heart disease: clinical implications

Background: Fractional Flow Reserve (FFR) in Stable Ischemic Heart Disease (SIHD) is universally accepted, while in Acute Coronary Syndromes (ACS) is less established. Aims of this retrospective study were: to compare in patients undergoing FFR assessment the prognostic impact of ACS vs SIHD, to evaluate the clinical relevance of the modality of utilization and timing of FFR assessment and to assess the different outcomes associated with an FFR> or ≤0.80. Methods: Major cardiac adverse events were assessed at a follow up of 16.4 ± 10.5 months in 543 patients with SIHD and 231 with ACS needing functional evaluation. FFR was used for lesions of ambiguous significance in the absence of a clear culprit vessel (first intention, FI) and for incidental lesions in the presence of a clear culprit vessel (second intention, SI). The decision to perform FFR and the identification of the stenosis needing functional assessment were left to the operator's discretion. Revascularization was performed when FFR was ≤0.80. Results: SIHD and ACS patients were not significantly different for principal clinical characteristics. ACS patients had significantly more events than SIHD, due to an excess of death and myocardial infarction. This was confirmed when FFR was used as FI, in particular if FFR was >0.80. On the contrary, when FFR was used as SI, event rates were similar between ACS and SIHD patients, regardless of FFR value. Conclusions: Our study shows that using FFR the risk of recurrent events in ACS is significantly higher than in SIHD. This different outcome is confined to those patients in whom FFR is utilized for lesions of ambiguous significance in the absence of a clear culprit vessel.