Importance The coronavirus disease 2019 (COVID-19) pandemic has changed health care delivery worldwide. Although decreases in hospitalization for acute myocardial infarction (AMI) have been reported during the pandemic, the implication for in-hospital outcomes is not well understood.

Objective To define changes in AMI case rates, patient demographics, cardiovascular comorbidities, treatment approaches, and in-hospital outcomes during the pandemic.

Design, Setting, and Participants This cross-sectional study retrospectively analyzed AMI hospitalizations that occurred between December 30, 2018, and May 16, 2020, in 1 of the 49 hospitals in the Providence St Joseph Health system located in 6 states (Alaska, Washington, Montana, Oregon, California, and Texas). The cohort included patients aged 18 years or older who had a principal discharge diagnosis of AMI (ST-segment elevation myocardial infarction [STEMI] or non–ST-segment elevation myocardial infarction [NSTEMI]). Segmented regression analysis was performed to assess changes in weekly case volumes. Cases were grouped into 1 of 3 periods: before COVID-19 (December 30, 2018, to February 22, 2020), early COVID-19 (February 23, 2020, to March 28, 2020), and later COVID-19 (March 29, 2020, to May 16, 2020). In-hospital mortality was risk-adjusted using an observed to expected (O/E) ratio and covariate-adjusted multivariable model.

Exposure Date of hospitalization.

Main Outcomes and Measures The primary outcome was the weekly rate of AMI (STEMI or NSTEMI) hospitalizations. The secondary outcomes were patient characteristics, treatment approaches, and in-hospital outcomes of this patient population.

Results The cohort included 15 244 AMI hospitalizations (of which 4955 were for STEMI [33%] and 10 289 for NSTEMI [67%]) involving 14 724 patients (mean [SD] age of 68 [13] years and 10 019 men [66%]). Beginning February 23, 2020, AMI-associated hospitalizations decreased at a rate of –19.0 (95% CI, –29.0 to –9.0) cases per week for 5 weeks (early COVID-19 period). Thereafter, AMI-associated hospitalizations increased at a rate of +10.5 (95% CI, +4.6 to +16.5) cases per week (later COVID-19 period). No appreciable differences in patient demographics, cardiovascular comorbidities, and treatment approaches were observed across periods. The O/E mortality ratio for AMI increased during the early period (1.27; 95% CI, 1.07-1.48), which was disproportionately associated with patients with STEMI (1.96; 95% CI, 1.22-2.70). Although the O/E mortality ratio for AMI was not statistically different during the later period (1.23; 95% CI, 0.98-1.47), increases in the O/E mortality ratio were noted for patients with STEMI (2.40; 95% CI, 1.65-3.16) and after risk adjustment (odds ratio, 1.52; 95% CI, 1.02-2.26).

Conclusions and Relevance This cross-sectional study found important changes in AMI hospitalization rates and worse outcomes during the early and later COVID-19 periods. Future studies are needed to identify contributors to the increased mortality rate among patients with STEMI.