BackgroundAlthough acute myocardial infarction (AMI) requires timely intervention, limited nationwide data is available regarding the association between disruption of emergency services and outcomes of patients with AMI during the coronavirus disease 2019 (COVID-19) pandemic. Moreover, whether diabetes mellitus (DM) adversely affects disease severity in these patients has not yet been investigated.MethodsThis nationwide population-based study analyzed 45,648 patients with AMI, using data from the national registry of emergency departments (ED) in Korea. Frequency of ED visits and disease severity were compared between the COVID-19 outbreak period (year 2020) and the control period (the previous year 2019).ResultsThe number of ED visits by patients with AMI decreased during the first, second, and third waves of the outbreak period compared to the corresponding time period in the control period (allp-values < 0.05). A longer duration from symptom onset to ED visit (p= 0.001) and ED stay (p= 0.001) and higher rates of resuscitation, ventilation care, and extracorporeal membrane oxygen insertion were observed during the outbreak period than during the control period (allp-values < 0.05). These findings were exacerbated in patients with comorbid DM; Compared to patients without DM, patients with DM demonstrated delayed ED visits, longer ED stays, more intensive care unit admissions (p< 0.001), longer hospitalizations (p< 0.001), and higher rates of resuscitation, intubation, and hemodialysis (allp-values < 0.05) during the outbreak period. While in-hospital mortality was similar in AMI patients with and without comorbid DM during the two periods (4.3 vs. 4.4%;p= 0.671), patients with DM who had other comorbidities such as chronic kidney disease or heart failure or were aged ≥ 80 years had higher in-hospital mortality compared with those without any of the comorbidities (3.1 vs. 6.0%;p< 0.001).ConclusionDuring the pandemic, the number of patients with AMI presenting to the ED decreased compared with that of the previous year, while the disease severity increased, particularly in patients with comorbid DM.