Emergency Department Management of Non–ST-Segment Elevation Myocardial Infarction

Table of Contents

 

Up to 25% of patients who present to the ED with chest pain are diagnosed with acute coronary syndromes (ACS). For the emergency clinician, it is critical to make the correct diagnosis, fast: STEMI, NSTEMI, unstable angina (or is it pulmonary embolism or just heartburn?).

What are the ECG criteria that differentiate STEMI and NSTEMI?

What are the different causes of STEMI and NSTEMI? Type 1 MI versus type 2?

Besides chest pain, what is the likelihood that other symptoms, such as nausea, dyspnea, and diaphoresis, are pointing to MI? Are these related to age, ethnicity, and sex?

What is the sensitivity of serial ECGs in detecting an occluding lesion?

How has the modified Sgarbossa criteria increased sensitivity for identifying MI?

What is the latest evidence on the value of high-sensitivity troponin assays?

Risk stratification scores: HEART, GRACE, TIMI: Which is best for the ED?

Is there new evidence on treatment strategies – analgesia, antiplatelets, anticoagulation?

What is the best ED management when you don’t know whether the patient’s further treatment strategy is going to be early-invasive or ischemia-guided?

1. Abstract
2. Opening Cases
3. Introduction
4. Critical Appraisal of the Literature
5. Etiology and Pathophysiology
6. Differential Diagnosis
7. Prehospital Care
8. Emergency Department Evaluation
   1. History
   2. Physical Examination
   3. Cardiac Monitoring
9. Diagnostic Testing
   1. Electrocardiogram
      1. ST-Segment Elevations
      2. ST-Segment Depressions
      3. Wellens Syndrome
      4. Left Bundle Branch Block and Sgarbossa Criteria
      5. de Winter Pattern
      6. Left Main Pattern
   2. Troponin
      1. High-Sensitivity Troponin
   3. Risk Stratification
   4. Imaging Studies
10. Treatment
    1. Anti-Ischemic Therapies
       1. Supplemental Oxygen
       2. Analgesia
    2. Antiplatelet Therapies
    3. Anticoagulant Therapies
    4. Beta Blockers
    5. Statins
    6. Ischemia-Guided Strategy Versus Early-Invasive Management Strategy
11. Special Populations
    1. Women Patients
    2. Black Patients
    3. Young Patients
    4. Diabetic Patients
    5. Cocaine-Associated Myocardial Infarction
12. Controversies and Cutting Edge
    1. Copeptin as a Biomarker for Acute Coronary Syndromes
13. Disposition
14. Summary
15. Time- and Cost-Effective Strategies
16. Risk Management Pitfalls for Management of NSTEMI in the Emergency Department
17. Case Conclusions
18. Clinical Pathways
    1. Clinical Pathway for Risk Stratification for STEMI and NSTEMI in the Emergency Department
    2. Clinical Pathway for Management of NSTEMI in the Emergency Department
19. Tables and Figures
    1. Table 1. American Heart Association/ American College of Cardiology Classes of Recommendation and Levels of Evidence
    2. Table 2. Clinical Features of Type 1 and Type 2 Myocardial Infarction
    3. Table 3. Differential Diagnosis of Chest Pain
    4. Table 4. Sgarbossa Criteria
    5. Table 5. HEART Score for Suspected Acute Coronary Syndromes
    6. Figure 1. Anterior STEMI on Electrocardiogram
    7. Figure 2. ST Depressions
    8. Figure 3. Wellens Pattern
    9. Figure 4. Sgarbossa Criteria
    10. Figure 5. Modified Sgarbossa Criteria
    11. Figure 6. The de Winter Pattern
    12. Figure 7. Left Main Pattern
20. References

Abstract

Chest pain is the second most common complaint in emergency departments, with 6.4 million visits annually in the United States. A quarter of these patients will be diagnosed with acute coronary syndromes, but among those, nearly half will have nondiagnostic electrocardiograms. Non–ST-segment elevation myocardial infarction (NSTEMI) is twice as common as ST-segment elevation myocardial infarction (STEMI), and lack of clarity surrounding the best management of this condition can contribute to adverse outcomes. In this review, current national management guidelines for NSTEMI are summarized as they pertain to the ED, and the evidence base supporting them is considered. Issues surrounding special patient populations are addressed, and new diagnostic and therapeutic modalities are discussed.

Opening Cases

A 76-year-old woman presents to the ED with chest pain. She said that for the past month she has been getting short of breath more easily on her daily walks, with occasional discomfort in her chest, requiring her to stop and rest. Two hours prior to ED arrival, she was doing yard work and developed chest pain that was much more severe. The pain is located in the center of her chest, and she describes it as a “pressure” sensation. Her only past medical history is hypertension. In the ED, her vital signs are within normal limits and her exam is unremarkable. Her ECG shows nonspecific ST-segment flattening, and her initial troponin is 0.09 ng/mL (reference range, 0-0.04 ng/mL). Your intern asks if she can go home since her troponin is low and she looks well...

A 69-year-old man presents to the ED with chest pain that began an hour prior to presentation, while he was walking home from the store. Initially, it felt similar to his usual episodes of angina, with left-sided pressure radiating to his left arm. However, the pain didn’t resolve with rest and has been worsening since onset, and is currently 9/10 in severity. He also notes dyspnea and lightheadedness. He has a history of hypertension, diabetes, and coronary artery disease, with baseline stable angina. His heart rate is 110 bpm and blood pressure is 90/40 mm Hg. He has bibasilar crackles and visibly increased work of breathing. Chest x-ray confirms your clinical suspicion of pulmonary edema. His ECG shows 4-mm anterior ST-segment depressions. His initial troponin is still pending. You wonder if you should activate the cath lab, or if a bedside echo might help...

An 82-year-old woman presents to the ED with chest pain. It started 3 hours prior to presentation during an argument with her husband, and she describes it as “squeezing,” localized to her left chest, with radiation to the neck and jaw. She has had several episodes of similar pain in the past, typically associated with emotional distress or exertion. She has never been evaluated by a doctor for it, as it typically resolves within 10 to 15 minutes with rest and relaxation techniques. Today, however, it has been more persistent and severe than usual. She has a past medical history of hypertension, diabetes, end-stage renal disease, and heart failure with reduced ejection fraction. Her vital signs are stable, and her exam is benign. Her ECG shows 3-mm ST-segment depressions in the lateral leads, and her troponin is 1.22 ng/mL. You start dual antiplatelet therapy and heparin, and her pain resolves. You admit her to the hospital, but wonder whether the inpatient team will take her to the cath lab or just manage her medically…

Introduction

In the United States, 6.3% of adults have coronary artery disease, and 3% have had a myocardial infarction (MI). This year, more than a million Americans will suffer MIs, meaning that an MI occurs approximately every 40 seconds.¹ There are approximately 6.4 million emergency department (ED) visits for chest pain annually in the United States, representing 5.3% of total visits, making chest pain the second most common reason for seeking ED care.² Among ED patients with chest pain, up to 25% will be diagnosed with an acute coronary syndrome (ACS), which includes STEMI (ST-segment elevation myocardial infarction), NSTEMI (non–ST-segment elevation myocardial infarction), and unstable angina.³ Effective management of patients with ACS is essential to minimize their risk for a major adverse cardiac event (MACE), including re-infarction, stroke, dysrhythmia, heart failure, cardiogenic shock, and death.

Emergency clinicians must be able to differentiate patients with cardiac ischemia from those with more benign causes of chest pain. Nonetheless, approximately 2% of patients presenting to EDs with ACS are misdiagnosed and inappropriately discharged.³ Misdiagnosis is most common among women younger than 55 years; other important risk factors for misdiagnosis include nonwhite race, presenting complaint of dyspnea, and normal or nondiagnostic electrocardiogram (ECG).⁴ Failure to hospitalize patients with ACS nearly doubles their mortality risk and is associated with significant legal liability.⁴

Myocardial infarction is defined as clinical evidence of acute myocardial ischemia in the setting of cardiac biomarker elevation above the 99^th percentile.⁵ Biomarker elevations in the absence of clinical ischemia are termed myocardial injury. Clinical evidence of ischemia may include any of the following:

• Characteristic signs and symptoms, eg, chest pain, diaphoresis
• New ischemic ECG changes
• Development of pathologic Q waves
• Imaging indicative of nonviable or compromised myocardium
• Coronary thrombus at angiography or autopsy

In patients with MI, it is essential to differentiate between STEMI and NSTEMI, as those with STEMI require emergent coronary intervention. STEMI is defined by ECG criteria in the presence of symptoms compatible with myocardial ischemia:⁵

• New ST-segment elevations ≥ 1 mm in 2 or more contiguous leads except V₂-V₃
• New ST-segment elevations in V₂-V₃ meeting these criteria:
  • ≥ 2.5 mm in men aged < 40 years
  • ≥ 2 mm in men aged > 40 years
  • ≥ 1.5 mm in women

Patients with MI who do not meet STEMI criteria are considered to have NSTEMI. NSTEMI is more common than STEMI, representing 60% to 70% of MIs.⁶ The incidence of STEMI has decreased in recent years, while the incidence of NSTEMI has remained stable or risen slightly.¹ In-hospital mortality rates are comparable between patients with STEMI and NSTEMI, at approximately 10%; however, the 1-year case fatality rate for patients with NSTEMI is more than double that for STEMI, at nearly 25%.⁶

This issue of Emergency Medicine Practice provides a comprehensive review of the literature on NSTEMI, the key diagnostic findings, and best-practice recommendations for management.

Critical Appraisal of the Literature

A PubMed search using the terms myocardial infarction [MeSH]) AND emergency service, hospital [MeSH] yielded 1905 articles, all of which were screened for relevance for this review. Because the majority of important literature addressing the diagnosis and management of MI is not specific to the ED setting, a broader strategy was needed. It was not feasible to conduct a comprehensive review using the term myocardial infarction [MeSH] alone, as this yielded 168,567 articles. We therefore augmented our ED-based search by reviewing national/international expert consensus guidelines, along with the literature cited by these guidelines, with additional targeted searches as needed.

In 2014, the American Heart Association (AHA) and the American College of Cardiology (ACC) released guidelines for NSTEMI management.⁷ It should be noted that the AHA/ACC have been criticized for possible conflict of interest due to extensive pharmaceutical industry funding of both the organizations themselves and their individual leaders.⁸ The European Society of Cardiology (ESC) released NSTEMI guidelines in 2015,⁹ and the American College of Emergency Physicians (ACEP) published a Clinical Policy on NSTEMI in 2018.¹⁰

The AHA/ACC and the ESC use a common system for grading the strength of recommendations and the supporting evidence. (See Table 1.) The ACEP policy translates levels of evidence into recommendation levels, wherein level A represents a high degree of clinical certainty, level B represents a moderate degree of clinical certainty, and level C represents a lack of clinical certainty. Recommendation classes cited in this article are from AHA/ACC, except where noted.

Risk Management Pitfalls for Management of NSTEMI in the Emergency Department

4. “I was taking care of an NSTEMI patient with a heart rate of 120 and blood pressure of 110/62 mm Hg. Pulmonary edema was noted on chest x-ray. I was worried about the heart rate, so I gave metoprolol 5 mg IV. Now the blood pressure is down to 80/40 mm Hg and he is in respiratory distress.”

Beta blockers should never be given to NSTE-ACS patients who have evidence of heart failure or shock. While beta blockers may be considered for stable patients, they should always be given orally. Furthermore, although patients with coronary artery disease benefit in the long term from being on a beta blocker, no benefit has been shown with administration in the first 24 hours.

5. “My chest pain patient is 68 years old and has a history of hypertension, diabetes, hypercholesterolemia, and morbid obesity. Her ECG is nonischemic, but she has left ventricular hypertrophy. Her pain has a ‘burning’ quality, and she associates it with indigestion. Her initial troponin is negative, and I really think this is just gastroesophageal reflux disease. I’m going to give her a GI cocktail and discharge her.”

Even with an unconvincing story, this patient has a HEART score of 4 (ECG, +1; age, +1; risk, +2), which puts her in a high-risk category. Serial troponin measurement is mandatory, and observation versus admission for further workup should be pursued.

6. “The NSTE-ACS patient had a history of heparin-induced thrombocytopenia, so I withheld anticoagulation and gave just aspirin.”

While most emergency clinicians have limited experience and comfort with alternate parenteral anticoagulants, agents such as fondaparinux and bivalirudin have been shown to be safe and effective in NSTE-ACS. These medications should be considered for patients with proven NSTE-ACS who have significant contraindications to heparins, and failure to administer them is not consistent with standard of care.

Tables and Figures

References

Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, randomized, and blinded trial should carry more weight than a case report.

To help the reader judge the strength of each reference, pertinent information about the study, such as the type of study and the number of patients in the study is included in bold type following the references, where available. In addition, the most informative references cited in this paper, as determined by the author, are highlighted.

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