ST-segment elevation myocardial infarction

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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)
    • Treat as STEMI
    • Look for reciprocal changes in anteroseptal leads (V1-V3)
    • Apply V7, V8, V9 leads and repeat ECG looking for ST elevation
    • Usually will see changes in V6 OR II, III, aVF

ACS Anatomical Correlation Chart

Ischemic Changes Location Coronary Artery
STE V1-V3, TWI

Q waves in V1-V3 over time

Septal Septal branch
STE V2-V4 Anterior LAD
STE I, aVL, V5, V6

STD inf leads

Lateral Circumflex
STE I, aVL, V2-6 Anterolateral LAD + circumflex = Left main or 2 critical lesions
STE II, III, aVF

STD in aVL (most common lead to see reciprocal change)

Inferior RCA

STE V1 (only lead looking at RV)
STE III > II (III more R facing)
STE V1 > V2, STE V1 + STD V2

Right ventricle RCA

STD in V1, V2, V3;
R>S in V1
Tall R waves in V1-V3 (Q waves on back of heart) w/ upright TWs

Posterior aka Inferolateral RCA (90%), LCA (10%)
STE avR>V1

Doesn't apply in SVT

Anterolateral Left Main

Prehospital

  • Refrain from oxygen therapy if patient is hypoxic as hyperoxia my increase myocardial injury[1]
  • Patients with a STEMI on the prehospital ECG but resolution of ST elevations on arrival still require activation of the cath team or transfer for primary catheterization even though there has been resolution of the ST-elevations[2]

Clinical Features

Risk of ACS

Clinical factors that increase likelihood of ACS/AMI:[3][4]

Clinical factors that decrease likelihood of ACS/AMI:[5]

  • Pleuritic chest pain
  • Positional chest pain
  • Sharp, stabbing chest pain
  • Chest pain reproducible with palpation

Gender differences in ACS

  • Women with ACS:
    • Less likely to be treated with guideline-directed medical therapies[6]
    • Less likely to undergo cardiac catheterization[6]
    • Less likely to receive timely reperfusion therapy[6]
    • More likely to report fatigue, dyspnea, indigestion, nausea or vomiting, palpitations, or weakness,[6] although some studies have found fewer differences in presentation[7]
  • More likely to delay presentation[6]
  • Men with ACS:
    • More likely to report central chest pain

Factors associated with delayed presentation[6]

  • Female sex
  • Older age
  • Black or Hispanic race
  • Low educational achievement
  • Low socioeconomic status

Differential Diagnosis

ST Elevation

Diagnosis

  • When possible, comparison to old ECGs should be performed
  • Repeating ECGs will increase sensitivity
  • Look for ST segment elevation, hyperacute T waves, and ST depression in reciprocal leads
  • Q waves are usually late, but may be early
    • Usually 1/3 amplitude of QRS
  • Use the J-point for measurement in 2 contiguous leads[8]
    • J point is where there is a sudden change in direction

Men

  • In males ≥ 40 years old 2mm in V2-V3 and 1mm in all other leads
  • In males < 40 years old 2.5mm in V2-V3 and 1mm in all other leads

Women

≥1.5 mm in V2-V3 and 1 mm (0.1mV) in all other leads

New LBBB

  • New LBBB alone is no longer STEMI criteria for cath lab as of 2013[9]
  • Sick patients with a new LBBB should be discussed with a cardiologist for possible coronary angiography

Sgarbossa's Criteria in LBBB

Original Criteria

Sgarbossa's Original Criteria

≥3 points = 98% probability of STEMI[10]

  • 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[11]

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%

Management

Defibrillation

  • Get the defibrillator ready early
  • Mortality in pts with vfib a function of time[12]

Adjunctive

  1. Aspirin 162-325mg chewable or 600mg PR
  2. Nitroglycerin
    • Do not give if RV MI
  3. Morphine
  4. Beta-Blocker:
    • PO within 24 hours
    • Options[13]
      • Acute MI: Metoprolol 5 mg IV q2 min for x3 doses, then PO metoprolol 50 mg q6hrs for 2 days starting 15 min after last IV dose, followed by maintenance of 100 mg bid
      • Post-MI: Atenolol 5 mg IV over 5 min, then repeat in 10 min, then PO atenolol 50 mg q12hrs for 7 days post-MI
    • IV beta-blocker is reasonable for patients who are hypertensive in the absence of:
      • Heart failure
      • Low cardiac output state
      • Cardiogenic shock risk factors
        • Age > 70yr, sys BP < 120, HR > 110 or <60,
      • Conduction block (PR interval > 0.24s, 2nd or 3rd block)
      • Active asthma
  5. O2
    • for SpO2 <90%
    • avoid hypoxia but supplemental O2 without hypoxia can increase infarct size[1]
      • AVOID trial[14] (2015) indicated larger infarct size, more recurrence and arrhythmia for STEMI pts without hypoxia who were treated with O2.

Antiplatelets

Clopidogrel

  • Loading dose of 600mg if PCI anticipated (otherwise give 300mg)
  • No loading dose if >75yr receiving fibrinolytics

Ticagrelor

  • May significantly reduce mortality as compared to clopidogrel[15]
  • 180 mg loading dose, followed by 90 mg BID
  • Ticagrelor offers no added benefit in STEMI when given pre-hospital vs. in-hospital (ambulance vs. cath lab)[16]

GPIIB/IIIa Inhibitors

  • Abciximab, Eptifibatide
  • Defer to cardiologist
  • Given right before PCI depending on specific institutional protocols

Anticoagulation

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

Definitive

The most critical aspect of care is to ensure systems are in place to minimize time taken for reperfusion. Anyone presenting within 12 hours of symptoms onset should have attempted reperfusion for STEMI. Options include fibrinolytic therapy or PCI. PCI is preferred if possible and had been demonstrated to result in superior outcomes.

  1. PCI
    • Goal: PCI should be attempted if the procedure can be started within 120 minutes (faster than 90 minutes is the goal, the faster the better)
    • if the PCI can't be commenced within 120 minutes then fibrinolysis should be given to suitable candidates
  2. Fibrinolytics
    • Goal: if it is determined that PCI can't be performed within 120 minutes then fibrinolytics should be given, and they should be given within 30 minutes
    • If receive fibrinolytics also give anticoagulants for minimum of 48hr, and preferable the length of the hospitalization
    • Fibrinolytic tx w/in 3hr resulted in >30 lives saved per 1000 pts
    • 0.5-1% of pts suffer ICH

Cardiac Arrest and STEMI

  • Consider hypothermia cooling protocol for patients with documented cardiac arrest felt to be caused by lethal cardiac rhythm (e.g. ventricular fibrillation)
  • Patients with cardiac arrest and ST elevation at any point, even if resolved, should still under go emergent coronary angiography[17]

Fibrinolysis

Alteplase (TPA)

Dosing based on patient weight:

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

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

Indications

  • <12hr from onset of CP
  • ST elevation of ≥1mm in 2 contiguous limb or precordial leads OR new LBBB
  • No PCI available within 90 min
    • Should be able to see ST elevation in RBBB

Contraindications

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

Relative contraindications

  1. Severe uncontrolled BP (>180/110)
  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)

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
  • Even in those with successful reperfusion, its reasonable to do angiography within the index hospitalization, although this should not be done within 2-3 hours of thrombolytic therapy.

Disposition

  • Admit direct to cath lab
  • If not at tertiary care center consider tPA depending transfer time and transfer to cardiac cath lab center

See Also

External Links

References

  1. ↑ 1.0 1.1 Stub D et al. Air versus oxygen in ST-Segment-Elevation Myocardial Infarction. Circulation. 2015;121:2143-2150
  2. ↑ Ownbey M, Suffoletto B, Firsch A, et al. Prevalence and interventional outcomes of patients with resolution of ST-segment elevation between prehospital and in-hospital ECG. Prehosp Emerg Care. 2014. Apr-Jun;18(2):174-9
  3. ↑ Body R, Carley S, Wibberley C, et al. The value of symptoms and signs in the emergent diagnosis of acute coronary syndromes. Resuscitation. 2010;81(3):281–286. PMID: 20036454
  4. ↑ Panju AA, Hemmelgarn BR, Guyatt GH, et al. The rational clinical examination. Is this patient having a myocardial infarction? JAMA. 1998;280(14):1256–1263. PMID: 9786377
  5. ↑ Swap CJ, Nagurney JT. Value and limitations of chest pain history in the evaluation of patients with suspected acute coronary syndromes. JAMA. 2005;294(20):2623–2629. PMID: 16304077
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Mehta LS, et al. Acute myocardial infarction in women: A scientific statement from the American Heart Association. Circulation. 2016; 133:916-947.
  7. ↑ Gimenez MR, et al. Sex-specific chest pain characteristics in the early diagnosis of acute myocardial infarction. JAMA Intern Med. 2014; 174(2):241-249.
  8. ↑ ACCF/AHA 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2013 Jan 29;61(4):e78-140. PDF
  9. ↑ Am Heart J 2013;166:409-13
  10. ↑ Sgarbossa E. et al.. "Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators". NEJM. 1996. 334(8):481-7
  11. ↑ Smith, S. et al. Diagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the ST-Elevation to S-Wave Ratio in a Modified Sgarbossa Rule. 60(6). 766-776
  12. ↑ Wilber DJ, Zareba W, Hall WJ, Brown MW, Lin AC, Andrews ML, Burke M, Moss AJ. Time dependence of mortality risk and defibrillator benefit after myocardial infarction. Circulation. 2004 Mar 9;109(9):1082-4.
  13. ↑ McAuley DF. Beta Blockers. GlobalRPH. http://www.globalrph.com/beta.htm
  14. ↑ Stub et al. Air Versus Oxygen in ST-Segment Elevation Myocardial Infarction. Circulation. 2015 May 22.
  15. ↑ Wallentin et Al. Ticagrelor versus Clopidogrel in Patients with Acute Coronary Syndromes. N Engl J Med 2009; 361:1045-1057.
  16. ↑ Montalescot G et al. Prehospital ticagrelor in ST-segment elevation myocardial infarction. N Engl J Med 2014 Sep 1.
  17. ↑ 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science PDF
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