In-hospital acute myocardial infarctions (AMI) are common and often lead to poor survival outcomes, a nested case-control, and matched cohort study found.
Incidence was 4.27 per 1,000 admissions among 1.3 million patients at U.S. Department of Veterans Affairs (VA) centers, reported Steven Bradley, MD, MPH, of Minneapolis Heart Institute, and colleagues in JAMA Network Open.
Factors linked with an increased risk of in-hospital AMI were history of elevated heart rate exceeding 100 beat/min, coronary artery disease, hemoglobin level under 8 g/dL, indicators of physiological stress, white blood cell count of 14,000/μL or more, and atherosclerosis.
Mortality was significantly greater for patients that had in-hospital AMI by comparison to the matched control group:
1-year mortality: 59.2% vs 34.4%
- 30-day mortality: 33.0% vs 10.0%
- In-hospital mortality: 26.4% vs 4.2%
Much of the existing literature has evaluated incidence of AMI outside of the hospital setting, and the findings from these investigations have contributed to declines in AMI death and incidence, the study authors noted.
When compared with individuals experiencing ST-segment elevation myocardial infarction (STEMI) onset outside the hospital, patients with in-hospital STEMI have had worse short-term outcomes and revascularization delays, they noted. But “less is known about the patient characteristics and long-term outcomes associated with in hospital AMI,” the researchers wrote.
Some research has compared outpatient onset AMI who survive to hospital admission and in-hospital AMI outcomes, possibly biasing comparisons of patient outcomes and characteristics. Moreover, STEMI only accounts for a small portion of all MIs, and there are a limited number of studies on in-hospital cases of non-STEMI (NSTEMI), the authors emphasized.
While the study provides foundational information about in-hospital AMI, future studies will have to determine optimal care delivery for it, said Bradley in an interview with MedPage Today.
The findings weren’t surprising, but are “useful in reminding physicians caring for hospitalized patients that in-hospital acute myocardial infarction is not a rare occurrence and in providing them with a set of risk factors to identify high-risk patients,” commented Daniel Blumenthal, MD, MPH, of Morehouse School of Medicine in Atlanta, who was not involved in the study.
Bradley’s group assessed 5,556 in-hospital AMI patients, with a mean age of 73 years and of whom 98.2% were male. They did a thorough medical record assessment on 687 cases and 687 individually matched controls from the in-hospital AMI group.
Patients with incidentally heightened troponin levels and without concurrent symptoms and signs of myocardial ischemia were excluded. Patients with AMI onset within 1 day of being admitted to the hospital were also excluded, to make sure that all cases of AMI actually took place in the hospital.
Outcomes and risk factors linked with in-hospital AMI were identified from matched comparison of hospitalized controls and in-hospital AMI cases. Using the entire cohort of in-hospital AMI relative to all the inpatient admissions, the investigators determined the incidence of in-hospital AMI.
All-cause 1-year readmissions occurred in 52.4% of the controls and 54.4% of cases, while readmissions for AMI occurred in 1.2% and 5.3%, respectively.
The researchers acknowledged the limitations of the study as: the cohort was predominately male, reliance on ICD-9 codes, lack of distinction between STEMI and NSTEMI, delays between data acquisition and data analysis due to administrative changes, and difficulty of assessment of participant risk factors close to the event.
Going forward, “additional research to define risk reduction and optimal treatment strategies of in-hospital AMI are needed to address this common and high-risk condition,” the authors concluded.
This study was supported by the Veterans Administration (VA) Clinical Studies Research and Development Program.
Bradley reported no conflicts of interest.