ST-elevation Myocardial Infarction (STEMI)

Background

• In patients presenting with symptoms of myocardial ischemia, ST-elevation myocardial infarction (STEMI) is defined by the combination of persistent ST-segment elevation and the subsequent release of biomarkers of myocardial necrosis.
• Other types of acute coronary syndromes include non-ST-elevation myocardial infarction (NSTEMI) and unstable angina (UA). NSTEMI is differentiated from UA by the presence of myocardial necrosis.
• STEMI is most often caused by plaque rupture of an atherosclerotic lesion in the affected (culprit) coronary artery followed by total occlusion of the vessel lumen with a thrombus. Selected nonatherosclerotic causes may also result in STEMI.
• Common risk factors for coronary artery disease (CAD) include tobacco abuse, dyslipidemias, hypertension, diabetes mellitus, and family history of CAD.

Evaluation

• Suspect STEMI in patients with symptoms consistent with the diagnosis, including chest pain or pressure. Other symptoms may include dyspnea, nausea and vomiting, diaphoresis, fatigue, or palpitations.
• Patients typically undergo a focused history and physical exam to assess the likelihood of STEMI and the early risk of adverse events.
• Signs and symptoms may suggest the presence of other complicating or mimicking conditions, such as aortic dissection and pericarditis. See the differential diagnosis section for other causes of signs and symptoms in patients suspected of having STEMI.
• Obtain a 12-lead electrocardiogram (ECG) within 10 minutes of first medical contact (Strong recommendation).
  • Diagnostic ST elevation in the absence of left ventricular hypertrophy or left bundle branch block (LBBB) include new ST elevation (at J point) and either of:
    • ≥ 2 mm (0.2 millivolts [mV]) in men or ≥ 1.5 mm (0.15 mV) in women in leads V2-V3
    • ≥ 1 mm (0.1 mV) in ≥ 2 contiguous chest leads or limb leads
• Consider additional posterior chest wall leads (V7-V9) in patients with a high suspicion of myocardial infarction and no diagnostic changes on the initial standard 12-lead ECG (Weak recommendation).
• Consider a repeat 12-lead ECG in patients with a high suspicion of myocardial infarction and no diagnostic changes on the initial standard 12-lead ECG.
• Consider additional right precordial leads (V3R and V4R) to assess for concomitant right ventricular infarction in patients with an inferior myocardial infarction (Weak recommendation).
• Obtain troponin T or troponin I as part of the initial diagnostic workup, but reperfusion treatment should not be delayed while results are pending because initial elevation may not be detectable for up to 6 hours after myocardial infarction (Strong recommendation).
• Perform emergency coronary angiography if there is significant clinical suspicion of an acute evolving myocardial infarction despite diagnostic uncertainty by electrocardiography.
• Consider imaging studies (echocardiography, chest x-ray) to assist in the diagnosis in uncertain cases, but imaging should not delay a transfer for coronary angiography (Weak recommendation).

Management

• Initial management should be directed at reducing myocardial ischemia, starting adjunctive antithrombotic therapy (antiplatelet and anticoagulant therapy), and identifying a reperfusion strategy that will restore blood flow to the culprit artery as quickly and as safely as possible as soon as the diagnosis of STEMI has been made, in order to minimize irreversible myocardial injury.
• Give aspirin 162-325 mg (chewed) as soon as STEMI is suspected.
• Give oxygen if arterial oxygen saturation (SaO₂) < 90% to prevent hypoxemia and maintain O₂ saturation > 90%.
• Give nitroglycerin 0.4 mg sublingually every 5 minutes (up to 3 doses) as needed for relief of discomfort due to ischemia, or start IV nitroglycerin for control of ischemia.
• Start reperfusion therapy in patients with persistent STEMI and symptoms of ischemia for ≤ 12 hours (Strong recommendation).
• Choose a reperfusion strategy:
  • For patients that present < 12 hours from symptom onset:
    • Perform primary percutaneous coronary intervention (PCI) if it can be done within 90 minutes of first medical contact (Strong recommendation) or if there is either:
      • a contraindication to fibrinolytic therapy (Strong recommendation)
      • acute severe heart failure or cardiogenic shock (Strong recommendation)
    • Administer fibrinolysis (in the absence of contraindications) within 30 minutes if PCI cannot be done within 120 minutes of first medical contact (Strong recommendation).
      • Perform angiography and PCI if indicated 2-24 hours after successful fibrinolysis (Strong recommendation).
      • Perform rescue PCI immediately if fibrinolysis fails, reocclusion occurs, or hemodynamic/electrical instability or worsening/recurrent ischemia presents (Strong recommendation).
    • Perform urgent coronary artery bypass graft (CABG) if high-risk features (such as ongoing/recurrent ischemia, cardiogenic shock, or severe heart failure) and coronary anatomy are not amenable to PCI (Strong recommendation).
  • For patients that present 12-24 hours from symptom onset, consider reperfusion strategies (similar to patients presenting < 12 hours from symptom onset) for patients with ongoing ischemia, with a large area of myocardium at risk, or who are hemodynamically unstable (Weak recommendation).
• Give a loading dose of P2Y12 inhibitor in addition to aspirin as soon as possible to all patients with STEMI (unless urgent CABG planned) such as (Strong recommendation):
  • clopidogrel (Plavix) 600 mg orally if the patient is having a primary PCI or 300 mg orally if the patient is ≤ 75 years old and treated with fibrinolytic therapy
  • alternatives to clopidogrel if having PCI include:
    • prasugrel (Effient) 60 mg orally, then 10 mg orally once daily
    • ticagrelor (Brilinta) 180 mg orally, then 90 mg orally twice daily
    • cangrelor IV if the patient is unable to tolerate oral medications or if no other P2Y12 inhibitors used at time of PCI
• Give anticoagulant therapy as follows (Strong recommendation):
  • if having primary PCI, use either IV unfractionated heparin or IV bivalirudin (Strong recommendation)
  • if treated with fibrinolytics, use IV unfractionated heparin, enoxaparin, or fondaparinux (Strong recommendation)
• Correct clinically significant bradyarrhythmia with a pharmacologic agent (for example, atropine) or with temporary pacing if symptomatic and unresponsive to medical therapy (Strong recommendation).
• See additional medical therapy section for medications (such as beta blockers, angiotensin converting enzyme inhibitors, aldosterone antagonists, and high-intensity statins) that may be warranted for some or all patients with STEMI.
• Prompt surgery is indicated for most mechanical complications after STEMI.
• Close follow-up consisting of additional testing, outpatient visits, and cardiac rehabilitation with aggressive lifestyle and risk factor modifications, medication compliance, psychosocial support, and education should be planned prior to hospital discharge.