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In-hospital AMI: Common and With Poor Outcomes (CME/CE)

Action Points

  • In-hospital acute myocardial infarction (AMI) was common — 4.27 in-hospital AMI events per 1,000 admissions at VA centers — and associated with increased post-discharge mortality compared with a matched control group (1-year mortality of 59.2% vs 34.4%).
  • Note that risk factors associated with in-hospital AMI included history of coronary artery disease, elevated heart rate, low hemoglobin level, and elevated white blood cell count.
  • Note that in-hospital AMI is common and is associated with prior cardiovascular disease, physiological disturbances, and poor survival.

CME Author: Zeena Nackerdien

Study Authors: Steven M. Bradley, Joleen A. Borgerding, et al.

Target Audience and Goal Statement:

Cardiologists, hospitalists, and intensivists

The goal was to learn more about the incidence, risk factors, and outcomes associated with in-hospital acute myocardial infarction (AMI).

Questions Addressed:

Study investigators addressed the following questions:

  • What were the risk factors, outcomes, and incidence of in-hospital AMI?
  • What were the differences between patients with in-hospital AMI and matched controls?

Synopsis and Perspective:

When blood flow to the heart is reduced or blocked — usually due to coronary artery disease — a part of the muscle is damaged or dies. Every 40 seconds, someone in the U.S. experiences such an AMI.

Getting to a hospital is paramount during the first hours following AMI. A new blood test has been developed to help identify or rule out an MI. According to the American Heart Association, the test measures for low levels of troponin T, a protein that is released into the blood when heart muscle is damaged by AMI. Depending on the severity of the AMI, the patient will be stabilized in an intensive care unit (ICU) and then spend a few days inside the medical facility.

But mortality rates for AMIs remain very high, approaching 50% for AMIs with cardiogenic shock. Nevertheless, the hospital remains the best setting for the patient. More than $300 million has been spent nationally to equip, train, and accredit doctors and hospitals in resuscitation care for in-hospital cardiac arrest.

What happens when a patient enters the hospital for another condition and experiences an AMI in the medical setting? The answer may depend on individual patient characteristics, type of AMI, and medical response. Damage that covers a large area of the heart and extends deep into the heart muscle is an ST-elevation MI (STEMI), which account for <25% of all MIs. Previous studies have shown that in-hospital STEMI cases experience delays in revascularization, and worse short-term outcomes, when compared with patients experiencing STEMI onset in the outpatient setting.

Non-STEMI (NSTEMI) differs from STEMI in numerous ways — they are caused by different types of blood clots and NSTEMI damage usually does not extend through the full depth of the heart muscle. There is a paucity of in-hospital AMI data that include NSTEMI.

Steven Bradley, MD, MPH, of Minneapolis Heart Institute, and colleagues, sought to address the literature gap because little is known about the full spectrum of in-hospital AMI cases.

This nested case-control and matched cohort study used U.S. Veterans Health Administration (VA) databases to identify in-hospital AMI cases and controls from July 2007 to September 2009.

Comparisons with controls were made by including patients (ages ≥50 at time of event) with in-hospital AMI who were admitted to a medical-bed service with a diagnosis other than ischemic heart disease, based on ICD-9 diagnosis codes. For comparison with the case patient, one control patient was randomly selected such that he or she was from the same hospital, was within 5 years of age, and was admitted within 90 days. Patients with incidentally elevated troponin levels in the absence of concurrent signs and symptoms of myocardial ischemia were excluded from the study.

External-Peer-Review-Program- (EPRP) abstractor-validated in-hospital AMI served as the outcome for the case control study of risk factors associated with in-hospital AMI. The primary outcome for the matched cohort study of outcomes following in-hospital AMI was all-cause mortality occurring in the year following the date of the index event, according to the authors. Secondary outcomes included in-hospital mortality, 30-day mortality, 1-year all-cause readmission, and admission for AMI.

Based on an AMI diagnosis >24 hours after admission to the same hospital, the investigators identified 5,556 patients with in-hospital AMI (98.2% male). This represented 4.27 AMI events per 1,000 admissions. A total of 687 cases of in-hospital AMI were matched to 687 control participants, and 85.4% were NSTEMI cases, while 14.6% were STEMI cases. Case patients had a mean age 73.3 and controls had a mean age 73.4.

In-hospital AMIs were more likely to occur in ICUs versus controls (27.1% vs 9.5%). Coronary risk factors (hypertension, hyperlipidemia, and diabetes) were more common in this vulnerable group versus controls.

In-hospital AMI cases also had a history of atherosclerotic disease (MI, percutaneous coronary intervention, coronary artery bypass graft, cerebrovascular disease, or peripheral vascular disease) and more moderate-to-severe anemia versus controls (68.8% vs 44.8%). Other risk factors associated with in-hospital AMI included a heart rate >100 beats/min, hemoglobin level <8 g/dL, and white blood cell count ≥14 000/μL.

Matched cohort analyses showed that in-hospital AMI patients experienced significantly higher mortality rates than controls with an in-hospital mortality of 26.4% vs 4.2%; a 30-day mortality of 33.0% vs 10.0%; and a 1-year mortality of 59.2% vs 34.4%. Lowest survival was observed following in-hospital STEMI. However, readmissions at 1 year were similar between cases and controls (54.4% vs 52.4%, P=0.52).

But generalizability of the results may be limited, because the case-control study was restricted to patients ages ≥50, with in-hospital AMI more than 24 hours after admission. The study also excluded postsurgical patients. Another limitation was the fact that incidence determination and subsequent nested case identification depended on ICD-9 codes with uncertain sensitivity and specificity characteristics for events occurring in the hospital.

Source Reference: JAMA Network Open, Jan. 18, 2019; 2:e187348. DOI:10.1001/jamanetworkopen.2018.7348

Study Highlights: Explanation of Findings

The findings showed that in-hospital AMI cases were common — 5,556 in-hospital AMI cases among 1.3 million admissions, amounting to an incidence of 4.27 per 1,000 admissions — and associated with prior cardiovascular disease, physiological disturbances, and poor survival (26.4% at 30 days and 59.2% at 1 year). Comparable literature values for AMIs that occurred outside of the hospital were 13% at 30 days and 25% at 1 year.

Spontaneous MI due to a primary coronary event such as plaque rupture or erosion is referred to as a type 1 MI by universal classification schema. Some in-hospital AMIs may be type 1 MIs, based on current findings that a history of atherosclerosis and risk factors for atherosclerosis contribute to the risk of an in-hospital AMI. Results may also reflect a common pathway of plaque disruption and thrombus formation.

Based on the 4th Universal Definition of Myocardial Infarction and earlier definitions, non-plaque disruption MIs are referred to as type 2 MIs and reflect an oxygen supply/demand mismatch. The present study also highlighted the potential of physiological disturbances consistent with type 2 MIs to contribute to in-hospital AMIs, such as severely low hemoglobin level, elevated heart rate, elevated serum urea nitrogen level, and elevated white blood count. Due to methodological challenges, no attempt was made to formally differentiate between type 1 and type 2 MIs from electronic health record review.

A mortality rate of nearly 60% at 1 year for in-hospital AMI is striking, especially when compared to a 1-year mortality of about 50% observed for bronchus and lung cancer, according to the authors.

While the study provides foundational information about in-hospital AMI, future studies will have to determine optimal care delivery for it, Bradley told MedPage Today.

The findings 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.

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