ST-segment elevation myocardial infarction

Background

• RV infarction accompanies ~25% of inferior STEMIs
  • Hemodynamically significant only 10% of the time
• Posterior infarction is rarely isolated (~3-8% of all AMIs)
  • Usually will see changes in V6 OR II, III, aVF

Diagnosis

Use the J-point for measurement in 2 contiguous leads:

1. Men ≥ 40yo:
   1. 2mm in V2-V3 and 1mm in all other leads
2. Men ≤ 40yo:
   1. 2.5mm in V2-V3 and 1mm in all other leads
3. Women:
   1. 1.5mm in V2-V3 and 1mm in all other leads

New LBBB

• New Left Bundle Branch Block is no longer a STEMI criteria for activation of the cath lab as of 2013
• Sick patients with a new LBBB should be discussed with a cardiologist for possible PCI

Sgarbossa's Criteria in LBBB

Original Criteria

Sgarbossa's Original Criteria

≥3 points = 98% probability of STEMI

• ST elevation ≥1 mm in a lead with upward QRS complex (concordant) - 5 points
• ST depression ≥1 mm in lead V1, V2, or V3 - 3 points
• ST elevation ≥5 mm in a lead with downward QRS complex (discordant) - 2 points

Smith's modification

Smith's Modified Sgarbossa 3rd Rule

• Changes the 3rd rule of original Sgarbossa's Criteria to be ST depression OR elevation discordant with the QRS complex and with a magnitude of at least 25% of the QRS
  • Increases Sn from 52% → 91% at the expense of reducing Sp from 98% → 90%

Anatomical Correlation

• See ACS - Anatomical Correlation

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)

• See also: ST Segment Elevation (DDX)

Treatment

Adjunctive

1. O2
   1. esp for SpO2 <90%
2. ASA 162-325mg chewable or 600mg PR
3. NTG
4. Morphine
5. 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

Antiplatelets

1. Clopidogrel
   1. Loading dose
      1. 600mg if PCI anticipated (otherwise give 300mg)
      2. No loading dose if >75yr receiving fibrinolytics
2. GPIIB/IIIa Inhibitors (Abciximab, Eptifibatide)
   1. Defer to cardiologist
   2. Given right before PCI

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

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 60min (i.e. 100mg over 1.5hr)
• ≤67kg pt:
  • Infuse 15mg IV over 1-2min; then 0.75 mg/kg (max 50mg) over 30 min; then 0.5 mg/kg over 60min (max 35 mg)

Dosing (Tenecteplase-TNKase)

• Reconstitute 50 mg vial in 10 mL sterile water (5 mg/mL)
• < 60 kg = 30 mg IV push over 5 seconds
• 60-69 kg = 35 mg IV push over 5 seconds
• 70-79 kg = 40 mg IV push over 5 seconds
• 80-89 kg = 45 mg IV push over 5 seconds
• > 90 kg = 50 mg IV push over 5 seconds

Rescue PCI

• Failed reperfusion: consider if repeat EKG 90 minutes after infusion fails to show reduction of elevated ST segments by 50%
• Recurrent significant ST elevation following successful lysis
• Persistent hemodynamically unstable arrythmias, persistent ischemic symptoms, or worsened cardiogenic shock

See Also

• Acute Coronary Syndrome (Main)
• ST Segment Elevation (DDX)
• EBQ:Sgarbossa Criteria Study
• http://emcrit.org/podcasts/left-bundle-branch-block/

Source

• Electrocardiography in Emergency Medicine. ACEP Textbook