No "July Effect" in the management and outcomes of acute myocardial infarction: An 18-year United States national study

Background: There has been conflicting reports on the effect of new trainees on clinical outcomes at teaching hospitals in the first training month (July in the United States of America). We sought to assess this "July effect" in a contemporary acute myocardial infarction (AMI) population.

Methods: Adult (>18 years) AMI hospitalizations in May and July in urban teaching and urban nonteaching hospitals in the United States were identified from the HCUP-NIS database (2000-2017). In-hospital mortality was compared between May and July admissions. A difference-in-difference analysis comparing a change in outcome from May to July in teaching hospitals to a change in outcome from May to July in nonteaching hospitals was also performed.

Results: A total of 1,312,006 AMI hospitalizations from urban teaching (n = 710,593; 54.2%) or nonteaching (n = 601,413; 45.8%) hospitals in the months of May and July were evaluated. May admissions in teaching hospitals, had greater comorbidity, higher rates of acute multiorgan failure (10.6% vs. 10.2%, p < 0.001) and lower rates of cardiac arrest when compared to July admissions. July AMI admissions had lower in-hospital mortality compared to May (5.6% vs. 5.8%; adjusted odds ratio 0.94 [95% confidence interval 0.92-0.97]; p < 0.001) in teaching hospitals. Using the difference-in-difference model, there was no evidence of a July effect for in-hospital mortality (p = 0.19).

Conclusions: There was no July effect for in-hospital mortality in this contemporary AMI population.