ST-segment elevation myocardial infarction

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Background

  • RV infarction may accompany up to 80% of inferior STEMIs
    • Hemodynamically significant only 10% of the time
  • Isolated posterior infarction is uncommon (~3-8% of all AMIs)
    • Usually will see changes in V6 or II, III, aVF

Diagnosis

  1. ≥ 1-mm (0.1mV) ST-segment elevation in at least 2 anatomically contiguous limb leads (aVL to III, including -aVR)
  2. ≥ 2-mm (0.2mV) ST-segment elevation in V1 through V3
  3. ≥ 1-mm ST-segment elevation in a precordial lead V4 through V6
  4. New left bundle branch block
    1. See also Sgarbossa's Criteria

DDx

  1. Myocardial ischemia or infarction
  2. Noninfarction, transmural ischemia (Prinzmetal's angina pattern or acute takotsubo cardiomyopathy)
  3. Post-MI (ventricular aneurysm pattern)
  4. Previous MI with recurrent ischemia in same area
  5. Pericarditis
  6. Early repolarization
  7. LVH or LBBB (only V1-V2 or V3)
  8. Myocarditis (may look like myocardial infarction or pericarditis)
  9. Brugada Syndrome
  10. Myocardial tumor
  11. Myocardial trauma
  12. Hyperkalemia (only leads V1 and V2)
  13. Hypothermia (J wave/Osborn wave)

Treatment

Adjunctive

  1. O2
    1. Esp for SpO2 <90%
  2. ASA 162-325mg chewable or 600mg PR
  3. Clopidogrel
    1. Loading dose
      1. 300mg
      2. 600mg if PCI anticipated
      3. No loading dose if >75yr receiving fibrinolytics
  4. NTG
  5. Morphine
  6. Beta-Blocker:
    1. PO within 24 hours
    2. IV beta-blocker is reasonable for patients who are hypertensive in the absence of:
      1. Heart failure
      2. Low cardiac output state
      3. Cardiogenic shock risk factors
        1. Age > 70yr, sys BP < 120, HR > 110 or <60,
      4. Conduction block (PR interval > 0.24s, 2nd or 3rd block
      5. Active asthma

Anticoagulation

  1. Heparin (UFH)
    1. Bolus 60U/kg (max: 4000U) followed by 12U/kg/h (max: 1000U/h)
    2. Titrate to PTT 1.5-2.5 x control
  2. LMWH
    1. <75yo with serum Cr < 2.5 mg/dL (men) or < 2.0 mg/dL (women):
      1. 30mg IV bolus followed by 1mg/kg SC q12h
    2. ≥ 75yo
      1. 0.75mg/kg SC q12h
    3. CrCl < 30 mL/min
      1. 1mg/kg SC qd
  3. Fondaparinux
    1. Cr < 3.0 mg/dL:
      1. 2.5mg IV bolus then 2.5mg SC qd started 24hr after bolus
    2. Monitor anti-Xa levels
  4. Bivalirudin
    1. 0.75mg/kg IV bolus followed by 1.75 mg/kg/h
    2. CrCl < 30 mL/min
      1. 0.75mg/kg IV bolus followed by 1.0 mg/kg/h

Antiplatelets

  1. GPIIB/IIIa Inhibitors (Abciximab, Eptifibatide)
    1. Defer to cardiologist
    2. Given right before PCI
  2. Clopidogrel
    1. 300mg po x1
    2. 600mg po x1 (if PCI is anticipated)

Definitive

  1. Fibrinolytics
    1. Goal: Give within 30min
    2. If receive fibrinolytics also give anticoagulants for minimum of 48hr
    3. Fibrinolytic tx w/in 3hr resulted in >30 lives saved per 1000 pts
    4. 0.5-1% of pts suffer ICH
  2. PCI
    1. Goal: Give within 90min (acceptable delay may be up to 120min)

Fibrinolysis

Indications

  1. <12hr from onset of CP AND:
    1. ST elevation of ≥1mm in 2 contiguous limb or precordial leads OR new LBBB

Contraindications

  1. Absolute contraindications
    1. Any prior ICH
    2. Known structural cerebral vascular lesion (AVM)
    3. Known intracranial neoplasm
    4. Ischemic stroke w/in 3 mo
    5. Active internal bleeding (excluding menses)
    6. Suspected aortic dissection or pericarditis
  2. Relative contraindications
    1. Severe uncontrolled BP (>180/100)
    2. History of chronic severe poorly controlled HTN
    3. History of prior ischemic stroke >3 mo
    4. Known intracranial pathology not covered in absolute contraindications
    5. Current use of anticoagulants with known INR >2–3
    6. Known bleeding diathesis
    7. Recent trauma (past 2 wk)
    8. Prolonged CPR (>10 min)
    9. Major surgery (<3 wk)
    10. Noncompressible vascular punctures (e.g. IJ, subclavian)
    11. Recent internal bleeding (within 2–4 wk)
    12. Pts treated previously with streptokinase should not receive streptokinase a 2nd time
    13. Pregnancy
    14. Active peptic ulcer disease
    15. Other medical conditions likely to increase risk of bleeding (diabetic retinopathy, etc)

Dosing (Alteplase)

  • >67kg pt:
  • Infuse 15mg IV over 1-2min; then 50mg over 30min; then 35mg over next hr
    • Total dose: 100 mg over 1.5hr
  • ≤67kg pt:
    • Infuse 15mg IV over 1-2min; then 0.75 mg/kg (not to exceed 50 mg) over 30 min; then 0.5 mg/kg over 60min (not to exceed 35 mg)

See Also

Source

  • ACC/AHA Practice Guidelines 2004/5
  • EBM 6/09
  • UpToDate
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