The following is a point-of-care summary of the January, 2020 Emergency Medicine Practice journal issue titled Emergency Department Management of Non–ST-Segment Elevation Myocardial Infarction, Click here for access to additional featured content from this issue, as well as subscription information. Subscribe or purchase a single issue and complete the activity to earn4 AMA PRA Category 1 Credits™. This summary is provided with the permission of our content partner EB Medicine.


Introduction

Emergency Department management of Non-St Segment Elevation Myocardial Infarction is written by Drs Julianna Jung and Sharon Bord.

  • Chest pain is the second most common ED complaint.
  • It bring 6.4 million visits to US EDs annually.
  • 25% will be diagnosed with ACS
  • 1/3 will have STEMI, 2/3 NSTEMI.

Guidelines reviewed include:

  • American Heart Association (AHA)
  • American College of Cardiology (ACC)
  • American College of Emergency Physicians (ACEP)
  • European Society of Cardiology (ESC)
  • Primary Literature

Definitions

  1. Myocardial Infarction: elevated cardiac biomarkers (aka troponin) with clinical evidence of acute myocardial ischemia (aka signs and symptoms, ECG changes, abnormal imaging, or coronary thrombosis at cath or autopsy).
  2. Myocardial injury, unfortunately also can be abbreviated as MI, but not in our discussion. This term refers solely to cases where biomarker elevation is present without any other clinical evidence for ischemia. 

Differentiating STEMI from NSTEMI relies solely on ECG findings. The most recent definition of these findings comes to use from the European Society of Cardiology’s  Fourth universal definition of myocardial infarction (2018). They define STEMI as one of two findings: 

  • ST elevation >1mm in two or more contiguous leads other than V2-V3
  • ST elevation in V2-V3
    1. > 2.5mm in med < 40 yrs old
    2. >2 mm in men > 40 yrs old
    3. >1.5mm in woman, regardless of age.

MACE= Major Adverse Cardiovascular Event: including re-infarction, stroke, dysrhythmia, heart failure, cardiogenic shock, and death.


Why Do We Care?

In-hospital mortality rates are about the same for STEMI and NSTEMI, about 10%. But it turns out that 1-year fatality rate in NSTEMI is more than double that of STEMI, at about 25% !(Am J med, 2011)


Pathophysiology

The European Society of Cardiology defines 6 types of MI. The only ones relevant to emergency medicine are type 1 and 2. The remainder classify procedure related MI, death related to coronary occlusion, CABG related MI and more. 

  • TYPE 1: MI (Infarction) is caused by insufficient coronary blood flow which, in the case of type 1 MI is related to atherosclerotic plaque rupture. This occludes the coronary and can occur at anytime, even if the underlying plaque is mild. This is the reason we don’t relay on prior cardiac caths the show no critical lesions, to rule out the possibility of ACS. 
  • TYPE 2: Type 2 MI is the “mismatch” MI that we hear our consultants talking about. These are the patients who had an imbalance in myocardial oxygen supply and demand.  This can be the result of hypotension, tachycardia, sepsis, PE, etc. These patients have higher hospital mortality and are more likely to die from non-cardiac causes.
  • Of the two types, this publication focuses on type 1 MI that does not cause ST elevation.  interestingly, these patients are more likely to have:
    • Absence of other serious medical conditions
    • Fewer comorbidities
    • Chest pain or anginal equivalent
    • ECG changes of ST depression or elevation
    • Higher troponin levels
    • Acute coronary occlusion due to plaque rupture, ulceration or dissection associated with thrombus

Pre-Hospital Care

There is insufficient high quality evidence for pre-hospital care or transport in NSTEMI. (Doesn’t mean it doesn’t help, just that we need more evidence). Much of what we do is extrapolated from STEMI care.  There is evidence in that arena to show:

  • Prehospital ECGs decrease time to intervention. (PCI in STEMI)
  • Early administration of aspirin decreases mortality and complications of MI (all types) and is safe in the pre-hospital setting (only 45% of get it during EMS transport, so room for improvement here).
  • Opioids (morphine) were associated with increased mortality in patients with NSTEMI in a 2015 study, but a 2016 review did not find any increased mortality in STEMI who received morphine pre-hospital so evidence is inconclusive.
  • Oxygen is increasingly being found to be harmful in excess. So, for hypoxic/dyspneic patients, one may give oxygen, otherwise, better to hold. 

ED Evaluation

History
There are conflicting studies regarding historical features that increase the likelihood of ACS in patients with chest pain. Never-the less, a UK study found the following features to be most associated with acute MI: 

  • Diaphoresis
  • Vomiting
  • Radiation of pain to both arms or shoulders
  • Radiation of pain to right shoulder
  • Although teaching has been that women have atypical presentations, a 2016 study did not support it. However, it did find that elderly patients and those with diabetes may present atypically. (dyspnea, fatigue, nausea, or epigastric pain)

Past Medical History

  • Family and personal history of CAD
  • Other medical diagnoses
  • Tobacco use
  • Illicit substance abuse
  • Age (CAD prevalence in age<40 is 1%, age >80 is 25%)
  • ** HIV
  • ** Cancer with history of radiation to the chest

Exam

  • Neurological deficits or unequal pulses may point to aortic dissection
  • A friction rub  may be heard in pericarditis 
  • A new murmur may represent papillary muscle rupture

Diagnostics

  • Telemetry – There has been much written about the low rates of arrythmia and the lack of need for telemetry. It’s important to keep in mind that this recommendation is in reference to patients with “low risk chart pain”  not NSTEMI. Different population. NSTEMI is still an indication for telemetry. 
  • ECG- Some patterns we should keep in mind when looking at ECGs in chest pain patients. These are best reviewed in the issue with the great samples given. But in brief;
    • ST elevation we talked about
    • ST depression >0.5mm in 2 contiguous leads.
    • Wellens Syndrome – deep symmetric T wave inversion or biphasic T waves in the precordial leads (V1-V6), associated with proximal LAD occlusion. Impending MI, not NSTEMI
    • Sgarbossa Criteria – This is the diagnosis of MI in the setting of known LBBB. It consists of three criteria
      • Concordant ST elevation > 1mm – Basically ST elevation in the same direction as the QRS
      • Concordant ST depression > 1mm V1-V3
      • Discordant ST elevation of at least 25% of the QRS (opposed to original 5 mm. using 25% increases sensitivity to 91%)
    • de Winter Pattern: 2% of LAD occlusions had ST depression at the J point with tall peaked T waves. A STEMI equivalent.
    • Left Main Pattern:
      • ST elevation > 1mm in aVR and
      • ST elevation in V1 of lower amplitude and
      • ST depressions diffusely
  • Troponin… you should get one. Better yet, get two. If you have high sensitivity troponins, there is much discussion regarding how these fit into advanced diagnostic protocols… more research is needed. 

Scoring systems

The HEART score has been show to outperform TIMI and GRACE for undifferentiated chest pain patients. There is still a role for TIMI and GRACE in the assessment of chest pain in patients with confirmed ACS. So don’t discount these scoring systems if your consultants use them later, but their applicability in the ED is not as good as the HEART Score.

Imaging in the ED: 

  • CXR
  • CT angiography and CT PE based on suspicion
  • CCTA is not indicated for patients with established NSTEMI, as the literature supporting its use is based on lower-risk patients with negative cardiac biomarkers.
  • Echocardiography – POC or formal – helpful to assess for depressed ejection fraction, pericardial effusion, or regional wall motion abnormalities.

Medications

Oxygen: AHA/ACC only if sat <90%, conflicting evidence about harm.

Morphine: ok to use, but not first line. There is association with worse outcome, but no good evidence of safety or harm in NSTEMI/ ACS. Remember that there is significant confounding with association drawn from observation. It may show worse outcome because these patients were sicker and didn’t respond to nitrates. We don’t know. So use, conservatively. 

Nitroglycerin: use it. Sublingual or IV, bolus or infusion, for pain or HTN or Hypertensive Emergency or CHF / pulmonary edema, etc. Don’t give if there is a history of phosphodiesterase inhibitors use (aka sildenefil, viagra, etc).

Aspirin reduced MACE in MI. It’s a class Ia recommendation INDEFINITELY in patients with ACS.


Antiplatelet Agents (P2Y12 inhibitors)

  • Clopidogrel (Plavix) is recommended with aspirin in NSTEMI . It further reduces MACE but not mortality in NSTEMI and it can be continued in those with aspirin sensitivity showing the same benefits in patients with CAD.
  • Ticagrelor (Brilinta) has been shown to have a lower incidence of MACE than clopidogrel among ACS patients. One study showed an increased risk of bleeding, but others have not. In addition, it was shown to be superior in patients with planned invasive management, persisting at 30 days and 1 year.  it is recommended by the AHA/ACC, ESC. 
  • Prasugrel (Effient) is another option. Currently not recommended prior to cath due to a study showing increase in bleeding risk without benefit in MACE reduction. (2014 guidelines). A more recent study found it to be superior to ticagrelor, but it was given after angiography and is not applicable to the ED.

Antipatelet IIb/IIIa inhibitors – eptifibatide (integrilin) and tirofiban (aggristat) have not been found to reduce MACE when given prior to angiography, therefore are rarely used in the ED.  Defer to cardiology as they may still be used in patients with known coronary anatomy. 

ACEP recommends aspirin as the only antiplatelet in the ED due to excessive bleeding complications. It is wise to allow our cardiology colleagues to guide specific antiplatelet agent use beyond aspirin. (If you are in a rural area, discussion with your referral center may be in order to create a regioanl guideline.)  


Anticoagulants (heparins) : In general, there is evidence that this category of medications is beneficial, even when combined with other anti-platelet agents. First proven to be of use in 1996 with a 33% reduction in MACE in patients with NSTEMI when combined with aspirin. 

  • Enoxaparin (Lovenox)
  • Fondiparinux (Arixtra) is synthetic and can be given to those with allergies to heparin. Found to be more advantagious in patients with CAD with lower bleeding risks. 
  • Bivalirudin (angiomax) also synthetic. 

Beta Blockers:

  • There is benefit to this class of medications. They reduce MACE, according to a 1989 study. 
  • There is some evidence that parentral injection in the ED can lead to an increase in cardiogenic shock. Risk factors for cardiogenic shock include:
    • Age > 70
    • SBP <120
    • Heart rate >110
    • History of CHF
    • No risk factors yielded 1.3% risk of shock, 8.1% for patient with 2 or more risk factors. 
    • Therefore, the AHA/ACC and ESC guidelines recommend administration in the first 24 hours, not immediately in the ED. 

Statins (HMG-CoA reductase inhibitors) have been shown to be helpful in the first 24 hours, especially in those who are statin naive. There is some suggestion that they are helpful even pre-cath in statin naive patients. 


Revascularization

Immediate/urgent revascularization is recommended for all patients with NSTEMI who show signs of clinical instability, including refractory angina, sustained ventricular dysrhythmias, new or worsening heart failure, or shock (AHA class Ia recommendation; ESC class Ic recommendation)
Otherwise, there is no clear benefit to immediate revascularization on all NSTEMI patients. Those at high risk do better at 6 months is they undergo early procedures(14-24 hours). This is a great time to have a conversation with cardiologists about risk scores- GRACE and TIMI- so the best decision for the patient can be made. Risk factors include: 

  • GRACE >140
  • New ST depression 
  • Troponin increase >20%

Special Populations

Women:

  • Men are twice as likely to have ACS. 
  • Woman who have ACS have higher short term mortality. 
  • AHA/ACC guidelines DO NOT recommend differences in management of NSTEMI based on gender. 
  • AHA/ACC guidelines DO note that revascularization is not beneficial in low-risk troponin -negative patients, particularly women. 

Black Patients:

  • Higher incidence of MI compared to white patients. 
  • Same male predominance. 
  • Black men 35-44 age, suffer 2.4 MI’s/1000 vs 0.8 for white men.
  • Black men 75-84 age, suffer 15.9 MI’s/1000 vs 9.1 for white men.
  • Risk for black women is lower than black men, but still higher than all gender white patients. 
  • Interestingly, mortality is higher following MI for blacks than whites. Black patients are less likely to undergo invasive management in NSTEMI, but this difference goes away when we look at STEMI. This suggests that “unambiguous standards of care and protocolized management” may help mitigate the issue of racial bias.

Young Patients: One study found 10% of MIs occur in patients <45 old.  Risk factor reduction is a big focus, with up to 90% being smokers. Other risks include family history of high cholesterol, obesity, and cocaine use.  But, long term they have lower risk of MACE and heart failure. 

Diabetics have higher incidence of MACE and mortality due to atypical presentations and delay in diagnosis. This is worse for insulin dependent patients.


Cocaine using patients with NSTEMI are treated as any other NSTEMI with one exception. Benzodiazepines become first line treatment.


References

  • Jung J, Bord S. Emergency department management of non-ST-segment elevation myocardial infarction. Emerg Med Pract. 2020;22(1):1-24. Issue , PubMed
  • Grunfeld C, Delaney JA, Wanke C, et al. Preclinical atherosclerosis due to HIV infection: carotid intima-medial thickness measurements from the FRAM study. AIDS (London, England). 2009;23(14):1841–9. PubMed
  • Holloway CJ, Ntusi N, Suttie J, et al. Comprehensive cardiac magnetic resonance imaging and spectroscopy reveal a high burden of myocardial disease in HIV patients. Circulation. 2013;128(8):814–22. PubMed
  • Borges N. Radiation-Induced CAD: Incidence, Diagnosis, and Management Outcomes. American College of Cardiology; 2018, May Article

This summary is provided with the permission of our content partner EB Medicine; http://www.ebmedicine.net

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