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.