Abstract Backgrounds Previous studies have demonstrated potential effect of excimer laser coronary atherectomy (ELCA) to reduce thrombus burden within the vessel, and ELCA has been used during primary PCI for acute coronary syndrome. Especially, the culprit lesions of ST-segment elevation myocardial infarction (STEMI) are generally accompanied by large thrombus burden. Nevertheless, the clinical effectiveness of ELCA use for the culprit lesions of STEMI has not been elucidated. Purpose To investigate the clinical outcomes of the STEMI patients who were treated with ELCA during primary PCI in comparison with those treated without ELCA. Methods We conducted the registry study of STEMI for the assessment of the efficacy of ELCA, which was an observational multicenter registry of the consecutive patients undergoing primary PCI for STEMI within 24 hours from the onset between 2015 and 2019. The patients were divided into two groups according to the use of ELCA during primary PCI: ELCA group and non-ELCA group. The primary endpoint was the major adverse cardiovascular event (MACE), which was defined as the composite of cardiovascular death (CVD), target vascular revascularization and non-fatal AMI. Propensity score (PS) matching was performed to adjust the bias of confounding factors using 1:1 nearest-neighbor matching without replacement. PS was yielded from clinical characteristics, baseline angiographic findings, and hemodynamic status that were imbalanced between the two groups. Results A total of 2593 patients, 424 patients in ELCA group and 2169 patients in non-ELCA group, were included in the analysis. PS matched cohort comprised 824 patients including 412 ELCA and 412 non-ELCA group. Median follow-up duration in the total cohort was 816 (394-1388) days. In the total cohort, baseline characteristics showed that younger age, less prevalent hypertension, and more frequent prior statin use in ELCA group than in non-ELCA group. In terms of clinical outcomes, ELCA group showed a significantly lower rate of CVD than non-ELCA group (4.3% vs 7.5%, P for log-rank = 0.03), whereas MACE rate was similar between the two groups (HR:1.00 95%CI 0.74-1.34, P=0.99). In the PS matched cohort, the baseline characteristics were well balanced. Clinical outcomes including MACE and CVD were comparable between the two groups (MACE HR:1.13 95%CI 0.76-1.66, P=0.53 and CVD HR0.70 95%CI 0.38-1.29 P=0.25). In the subgroup analysis, MACE rate was lower in ELCA group than in non-ELCA group in the patients who presented with Killip class III or IV (P for interaction <0.01) (Abstract Picture 1). Conclusions The use of ELCA was not associated with improved MACEs in both total cohort and the PS matched cohort, whereas subgroup analysis suggested a potential benefit of ELCA in patients with heart failure. Further prospective investigations are warranted.Forest Plots for Subgroup Analysis