Definition¹:

• Acute Coronary Syndrome includes:
  • ST Elevation Myocardial Infarction (STEMI).
  • Non-ST Elevation Myocardial Infarction (NSTEMI).
  • Unstable Angina (UA).
  • Each includes clinical symptoms and signs of unstable ischemia.
    • +/- new ECG ischemic changes.
  • Differentiator is elevated troponin in STEMI / NSTEMI.
    • No change in troponin in UA.
• Clinical Classification of MI:
  • Type 1:  Atherosclerotic plaque rupture.
  • Type 2:  demand ischemia: O2 supply-demand mismatch.
  • Type 3:  ECG ischemic features but unexpected death prior to drawing troponins.
  • Type 4a/4b:  MI related to percutaneous coronary intervention.
  • Type 5:  MI related to CABG.
• Elderly, diabetics, and women can have atypical presentations and warrant careful evaluation.

• Patient outcomes improved with early diagnosis and treatment².
• Management often concurrent with diagnostic process.
• Rapid assessment and initial management = < 10 mins of presentation (includes history, physical, ECG, troponin bloodwork drawn).
• Determine if ACS and if ACS: UA versus NSTEMI versus STEMI.
• Features suggestive of ACS angina:
  • Rest angina (‘usually’ greater than 20 mins), new onset angina with marked impairment in physical activity, progressively worsening baseline angina.
  • NSTEMI and UA diagnosis is made with or without ECG changes.  Difference between them is degree of ischemia able to cause myocardial damage and releasing troponin.
  • UA:  Clinical presentation of ischemic symptoms but no elevation of troponins +/- new ischemic ECG changes.  Clinical history very important.
  • NSTEMI:  Clinical presentation of ischemic symptoms with elevation of troponins +/- new ischemic ECG changes.
• History:
  • Ischemic Chest Pain Characteristics:
    • Gradual onset, worse with exertion, no changes with respiration or position, may have some relief with nitroglycerin.
    • Pain can be difficult to describe – “squeezing, tightness, pressure, constriction, crushing, burning, lump in throat”.  Usually not described as sharp.
    • Radiation of pain to other parts of body – upper arms, neck, back.
    • Diffuse pain rather than specific spot
    • Stable angina usually 2-5 mins and relieved with rest or Nitroglycerin.
    • UA = new onset, worsening pain (intensity/duration) with less exertion/at rest; less relief with NTG/rest.
    • ACS chest pain generally lasts longer than 30 mins.

*Note:  Relief of chest pain following trial of GI cocktail of antacid (+/- viscous lidocaine) or relieve with nitroglycerin cannot reliably rule in/out ischemic chest pain.

• Non-ischemic chest pain (less likely ACS):
  • Pleuritic pain related to respiration.
  • Localizable with finger.
  • Reproducible.
  • Constant lasting days.
  • Pain lasting few seconds.
  • Associated symptoms:  shortness of breath, nausea, indigestion, vomiting, diaphoresis, dizziness, fatigue.
  • Past medical history: prior ACS, vascular disease.
  • Risk factors:  age, male, diabetes, hypertension, dyslipidemia, smoking, cocaine use, family history positive ACS or sudden death.

Elderly, diabetics and women may not have chest pain but instead dyspnea, nausea or vomiting, weakness, etc.

• Physical Exam:
  • Targeted:
    • Cardiogenic shock:  hypotension, tachycardia, altered level of consciousness, cool/pale skin.
    • Heart Failure:  elevated JVP, lung crackles, hypotension, tachycardia, mitral regurgitation murmur.
    • Neuro examination: helps in decision making regarding possible use of thrombolytic therapy.
  • Otherwise full cardiac, respiratory, abdominal examination is warranted.
• Differential Diagnosis:

Table 1: Adapted from UpToDate: Initial evaluation and management of suspected acute coronary syndrome (myocardial infarction, unstable angina) in the emergency department.

• Investigations specifically for ACS¹:
  • Troponin:
    • Abnormal when >= 99 percentile upper limit normal (varies per assay)
    • Use in clinical context, non-specific elevations seen (e.g. in Chronic Kidney Disease, Sepsis).
    • In patients with chronic elevations, use rise or fall in troponin values.
    • Serial testing is important.  Most patients with acute MI can be ruled out by 6 h.  If high degree suspicion 12 h sample should be taken.
    • Recommended:
      • Measure at first presentation.
      • Repeat in 3-6 h (80% patients found to have elevation in 2-3 h).
      • Shorter periods for high sensitivity troponins.

Don’t delay treatment in suspected STEMI cases for troponin values.

• ECG:
  • NSTEMI vs STEMI:
    • Elevation in troponin but differences in ECG changes.
• ECG of UA/NSTEMI:  No abnormalities, ST-segment depression, T wave inversion.
  • Definition: “new horizontal or downsloping ST-depression ≥0.5 mm in two contiguous leads and/or new T wave inversion >1 mm in two contiguous leads with prominent R wave or R/S ratio >1”.
  • ST-T wave changes can be seen diffusely or localize to region of ischemia.
  • ST-T ECG changes often persistent in NSTEMI vs transient in UA.
  • Absence of ST segment elevation or pathological Q waves.
  • T-wave inversion can be normal variant in leads III, aVR, V1.
  • Upsloping ST Depression is non-specific for myocardial ischemia.
  • Greater degree of ST Depression is associated with worse prognosis.

Image 1: Example of ST segment depression. Source: https://litfl.com/myocardial-ischaemia-ecg-library/

Image 2: 12 lead ECG showing ST segment depression. Source: https://litfl.com/myocardial-ischaemia-ecg-library/

Image 3: New T wave inversion. Source: https://litfl.com/myocardial-ischaemia-ecg-library/

• ECG of STEMI:  New ST-segment elevation at J point in 2 contiguous leads:  ≥1 mm all leads:
  • ≥2 anterior or inferior or posterior leads (NOTE 2 mm elevation anteriorly no longer threshold – in Vancouver at least).
  • ST segment elevation differential includes:
    • Acute myocardial ischemia.
    • acute pericarditis, myocarditis.
    • benign early repolarization.
    • massive PE.
    • Brugada-type patterns.
    • Old MI and persistent ST segment elevation.
  • Can also manifest as new LBBB or patients with a true posterior MI.
  • Inferior wall ischemia (leads II, III, aVF) should prompt right sided leads for possible RV infarct.
    • ST segment depression in inferior leads should also prompt posterior leads for possible posterior infarct.
• Note:  Non-diagnostic ECGs are common.  If suspicion for ACS high, repeat ECG at 20-30 min intervals.
• ECG features suggestive of prior MI:
  • Abnormal Q waves.

Aside: Can also have imaging evidence of myocardial ischemia.

Diagnostic Algorithm:

Figure 1: ACS Diagnostic Pathway.^{2,4, 6}

1. Hooton TM, Gupta K. Diagnosis of acute myocardial infarction. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2020.

   
   

2. Hooton TM, Gupta K. Initial evaluation and management of suspected acute coronary syndrome (myocardial infarction, unstable angina) in the emergency department. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2020.

   
   

3. Hooton TM, Gupta K. Acute coronary syndrome: Terminology and classification. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2020.

   
   

4. Hooton TM, Gupta K. Overview of the acute management of non-ST elevation acute coronary syndromes. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2020.

   
   

5. https://litfl.com/myocardial-ischaemia-ecg-library/

   
   

6. Barstow et al. Acute Coronary Syndrome: Diagnostic Evaluation.  Am Fam Physician. 2017;95(3):170-177.

   
   

20210616 Appendix – Ischemic Pain Suspected Initial Management Orders + STEMI and NSTEMI Algorithms