Quantitative flow ratio-guided residual functional SYNTAX score for risk assessment in patients with ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention

Background: Functional incomplete revascularisation (IR) is associated with a higher risk of major adverse cardiac events (MACE) during long-term follow-up in patients with ST-segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI). Aims: This study aimed to investigate the prognostic ability of quantitative flow ratio (QFR)-guided residual functional SYNTAX score (Q-rFSS) and functional IR in STEMI patients undergoing PCI. Methods: In total, 354 consecutive STEMI patients who successfully underwent PCI were included. Q-rFSS was defined as residual SYNTAX score (rSS) measured only in vessels with QFR <= 0.8. The primary outcome was MACE (a composite of all-cause mortality, myocardial infarction, and ischaemia-driven revascularisation) at 2 years. Results: At two-year follow-up, functional IR (Q-rFSS >= 1) showed significantly higher risk for MACE than functional complete revascularisation (CR) (Q-rFSS=0) (functional IR vs CR, 22.0% vs 7.4%; hazard ratio [HR] 3.21; 95% confidence interval [Cl]: 1.74 to 5.91; p<0.001). The area under the curve (AUC) of Q-rFSS (0.738, 95% CI: 0.659 to 0.817) was significantly greater than that of rSS (0.648, 95% CI: 0.547 to 0.749). The C-statistic for MACE also increased after the addition of Q-rFSS to the clinical risk factors. Q-rFSS significantly improved risk classification compared with rSS (net reclassification improvement 0.439, 95% CI: 0.201 to 0.548; p<0.001). Conclusions: Functional IR is associated with higher risk of MACE during long-term follow-up in STEMI patients undergoing PCI. Q-rFSS has a better prognostic ability for the risk of MACE.