Incidence, Risk Factors, and Outcomes Associated With In-Hospital Acute Myocardial Infarction

Abstract

Importance: Studies of acute myocardial infarction (AMI) occurring outside the hospital have informed approaches to addressing risk, treatment, and patient outcomes. Similar insights for in-hospital AMI are lacking.

Objective: To determine the incidence, risk factors, and outcomes associated with in-hospital AMI.

Design, setting, and participants: Cohort, nested case-control, and matched cohort study of patients hospitalized in US Veterans Health Administration facilities between July 2007 and September 2009. The incidence of in-hospital AMI was determined from a complete cohort of in-hospital AMI relative to the total number of inpatient admissions. From the in-hospital AMI cohort, detailed medical record review was performed on 687 cases and 687 individually matched controls. Risk factors and outcomes associated with in-hospital AMI were determined from matched comparison of in-hospital AMI cases to hospitalized controls.

Exposures: Candidate risk factors for in-hospital AMI included characteristics at the time of admission and in-hospital variables prior to the index date.

Main outcomes and measures: In the determination of the incidence and risk factors associated with in-hospital AMI, the outcome of interest was in-hospital AMI. All-cause mortality was the main outcome of interest following in-hospital AMI.

Results: A total of 5556 patients with in-hospital AMI (mean [SD] age, 73 [10] years; 5456 [98.2%] male) were identified among 1.3 million admissions, with an incidence of 4.27 in-hospital AMI events per 1000 admissions. Independent risk factors associated with in-hospital AMI included intensive care unit setting, history of coronary artery disease, heart rate greater than 100 beats/min, hemoglobin level less than 8 g/dL, and white blood cell count 14 000/μL or greater. Compared with the matched control group, mortality was significantly higher for patients with in-hospital AMI (in-hospital mortality, 26.4% vs 4.2%; 30-day mortality, 33.0% vs 10.0%; 1-year mortality, 59.2% vs 34.4%).

Conclusions and relevance: In-hospital AMI was common and associated with common cardiovascular risk factors and markers of acute illness. Patient outcomes following in-hospital AMI were poor, with 1-year mortality approaching 60%. Further study of in-hospital AMI may yield opportunities to reduce in-hospital AMI risk and improve patient outcomes.

Figure 1.. Selection of In-Hospital Acute Myocardial Infarction (AMI) Cases

EPRP indicates External Peer Review Program; VA, Veterans Affairs.

Figure 2.. Kaplan-Meier Survival Curves for the Matched Cohort with In-Hospital Acute Myocardial Infarction (AMI) Cases Stratified by ST-Segment Elevation Myocardial Infarction (STEMI) and Non–ST-Segment Elevation (NSTEMI)

The shaded areas show 95% confidence intervals.