Distribution, management and outcomes of AMI according to principal diagnosis priority during inpatient admission

Background: In recent years, there has been a growing interest in outcomes of patients with acute myocardial infarction (AMI) using large administrative datasets. The present study was designed to compare the characteristics, management strategies and acute outcomes between patients with primary and secondary AMI diagnoses in a national cohort of patients.Methods: All hospitalizations of adults (≥18 years) with a discharge diagnosis of AMI in the US National Inpatient Sample between January 2004 and September 2015 were included, stratified by primary or secondary AMI. The International Classification of Diseases, ninth revision and Clinical Classification Software codes were used to identify patient comorbidities, procedures and clinical outcomes.Results: A total of 10,864,598 weighted AMI hospitalizations were analysed, of which 7,186,261 (66.1%) were primary AMIs and 3,678,337 (33.9%) were secondary AMI. Patients with primary AMI diagnoses were younger (median 68 vs. 74 years, p<0.001) and less likely to be female (39.6% vs. 48.5%, p<0.001). Secondary AMI was associated with lower odds of receipt of coronary angiography (aOR 0.19; 95%CI 0.18-0.19) and percutaneous coronary intervention (0.24; 0.23-0.24). Secondary AMI was associated with increased odds of MACCE (1.73; 1.73-1.74), mortality (1.71; 1.70-1.72), major bleeding (1.64; 1.62-1.65), cardiac complications (1.69; 1.65-1.73), and stroke (1.68; 1.67-1.70) (p<0.001 for all).Conclusions: Secondary AMI diagnoses account for one-third of AMI admissions. Patients with secondary AMI are older, less likely to receive invasive care and have worse outcomes than patients with a primary diagnosis code of AMI. Future studies should consider both primary and secondary AMI diagnoses codes in order to accurately inform clinical decision-making and health planning