Background:Selective use of distal filter protection during percutaneous coronary intervention (PCI) for acute coronary syndromes (ACS) decreased the incidence of no-reflow phenomena and in-hospital serious adverse cardiac events compared with conventional PCI in patients with attenuated plaque ≥5 mm; however, its long-term clinical outcome remains unknown.Methods and Results:Patients who had ACS with attenuated plaque ≥5 mm were assigned to receive distal protection (DP) (n=98) or conventional treatment (CT) (n=96). The rate of major adverse cardiovascular events (MACE), a composite of death from any cause, non-fatal myocardial infarction, or target vessel revascularization (TVR) at 1 year, was the pre-specified secondary endpoint of the trial. MACE at 1 year occurred in 12 patients (12.2%) in the DP group and 3 patients (3.1%) in the CT group (P=0.029), which was driven by a higher risk of TVR (11 11.2% vs. 2 2.1%, P=0.018). In patients treated with bare-metal stents (n=42), MACE occurred in 25.0% of the patients in the DP group and in none of the patients in the CT group (P=0.029), whereas in patients treated with drug-eluting stents (n=151), rates of MACE were similar in the groups (8.1% vs. 3.9%, P=0.32).Conclusions:In ACS patients with attenuated plaque ≥5 mm, the 1-year rates of MACE were higher in the DP group than in the CT group. This effect might be mitigated by the use of drug-eluting stents.