DESCRIPTION

• Cardiac reperfusion therapy is required on patients that present with ST-segment elevation myocardial infarction (STEMI)
• Early percutaneous coronary intervention (PCI), but not fibrinolytics may be considered in those with unstable angina (UA)/non–ST-segment elevation MI (NSTEMI)
• Fibrinolytic therapy:
  • Reduces morbidity and mortality in STEMI in cases that PCI is not available in < 120 min
  • The earlier fibrinolytics are started, the more myocardium is salvaged
  • Goal of fibrinolytic therapy is a door-to-needle time of 30 min if PCI is not planned or delayed > 120 min
• PCI:
  • Balloon inflation, stent placement, and thrombus removal are possible options in the cath lab and result in overstretching of vessel wall and partial disruption of intima, media, and adventitia, resulting in enlargement of lumen and outer diameter of diseased vessel and restoration of epicardial coronary arterial flow
  • Goal of primary PCI is a door-to-balloon time of 90 min from 1st medical contact for STEMI or < 120 min if at a non-PCI center
  • Stent placement decreases early and late loss in luminal diameter seen with percutaneous transluminal coronary angioplasty (PTCA).
  • PCI provides greater coronary patency and thrombolysis in MI flow than do fibrinolytics and decreased mortality and morbidity
  • Lower risk of bleeding than with fibrinolytics
  • Immediate knowledge of extent of disease
  • PCI should be strongly considered within 1st 48 hr after NSTEMI in discussion with a cardiologist
• Glycoprotein IIb/IIIa inhibitors:
  • Antiplatelet agents that bind to platelet receptor glycoprotein IIb/IIIa and inhibit platelet aggregation
  • Reduce mortality and reinfarction rate in patients in whom PCI is planned; reasonable to administer at time of primary PCI
  • Not indicated for patients with STEMI, unless also undergoing PCI
• Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH):
  • Adjuncts in treatment with aspirin, clopidogrel, fibrinolytics, glycoprotein IIb/IIIa inhibitors, and PCI
  • Anticoagulant therapy with either UFH or LMWH is indicated in patients with either STEMI (with PCI or fibrinolytics) or UA/NSTEMI
• Clopidogrel or Prasugrel should be added to standard therapy regardless of whether PCI or reperfusion therapy is planned.
• Statin therapy reduces clinical events in patients with stable coronary artery disease. This may also extend to patients experiencing an acute ischemic coronary event
• Post arrest patients may have therapeutic hypothermia initiated in the ED prior to PCI or during PCI

ETIOLOGY

• STEMI is caused by occlusion of an epicardial coronary artery, usually as a result of a thrombotic event
• UA/NSTEMI is caused by a partial occlusion of coronary artery, also due to thrombus.

[Outline]

• DESCRIPTION
• ETIOLOGY

SIGNS AND SYMPTOMS

• Chest pain, heaviness, or pressure feeling
• Shortness of breath
• Arm, neck, or back pain
• Weakness or fatigue
• Nausea, vomiting
• Diaphoresis
• Palpitations
• Dizziness or syncope
• STEMI ECG

ESSENTIAL WORKUP

• History is critical in assessing window for use of both fibrinolytics and PCI.
• ECG:
  • Will be normal ~50% of time
  • Must be compared with prior tracings if available and may evolve in short period of time, consider repeat ECGs
  • ST elevation in the absence of left ventricular hypertrophy or left bundle branch block (LBBB) with new ST elevation at the J point in at least 2 contiguous leads of ≥2 mm in men or ≥1.5 mm in women in leads V₂–V₃ and/or of ≥1 mm (0.1 mV) in other contiguous chest leads or the limb leads (7)
  • New or presumably new LBBB has been considered a STEMI equivalent. Most cases of LBBB at time of presentation; however, are "not known to be old" because prior ECG is not available for comparison.
  • New or presumably new LBBB at presentation occurs infrequently, may interfere with ST-elevation analysis, and should not be considered diagnostic of acute myocardial infarction (MI) isolation without symptoms of ACS; use of Sgarbossa criteria is recommended for definitive diagnosis
  • Baseline ECG abnormalities other than LBBB (e.g., paced rhythm, LV hypertrophy, Brugada syndrome) may obscure interpretation
  • New ST-segment changes or T-wave inversions are suspicious for UA or non–Q-wave infarct
  • 1-mm depression of the ST segment below the baseline, 80 ms from the J point, is characteristic of UA or non–Q-wave infarct
• Chest radiograph: May be helpful if aortic dissection is being considered
• Heme stool test: Helpful in establishing baseline, especially in setting of anticipated anticoagulation

DIAGNOSIS TESTS & INTERPRETATION

Lab

• Cardiac enzymes, troponin preferred
• Baseline creatinine, hematocrit, and coagulation profile are all appropriate in initial workup.

DIFFERENTIAL DIAGNOSIS

• Aortic dissection
• Anxiety
• Biliary colic
• Coronary aneurysm
• Costochondritis
• Esophageal spasm
• Esophageal reflux
• Herpes zoster
• Hiatal hernia
• Hyperkalemia
• Mitral valve prolapse
• Peptic ulcer disease
• Psychogenic symptoms
• Panic disorder
• Pericarditis
• Pneumonia
• Pulmonary embolus
• Ventricular aneurysm

[Outline]

• SIGNS AND SYMPTOMS
• ESSENTIAL WORKUP
• DIAGNOSIS TESTS & INTERPRETATION
• DIFFERENTIAL DIAGNOSIS

PRE-HOSPITAL

• IV access
• Oxygen
• Cardiac monitoring
• Sublingual nitroglycerin for symptom relief, unless use of phosphodiesterase inhibitor in the last 24 hr
• Aspirin 162 or 325 nonenteric coated
• Local EMS system and hospital system should preferentially transport STEMIs to PCI-capable hospital
• Controversies:
  • Whether to allow EMS activation of cardiac catheterization labs and administration of fibrinolytics.

ALERT

INITIAL STABILIZATION/THERAPY

• IV access
• Oxygen
• Cardiac monitoring
• Oxygen saturation
• Continuous BP monitoring and pulse oximetry
• Nitrates
• Therapeutic hypothermia if indicated post arrest

ED TREATMENT/PROCEDURES

• Aspirin
• Clopidogrel
• Fibrinolytics for STEMI
  • Unless contraindicated
  • If PCI is not readily available within 120 min
• PCI is preferred for both diagnostic and therapeutic options for STEMI and UA/NSTEMI
• PCI and fibrinolytics therapy must be used with either UFH or an LMWH, such as enoxaparin or bivalirudin
• LMWH:
  • Kinetics more predictable
  • Requires no monitoring
  • Less potential for platelet activation
  • Lower bleeding rate
  • Is at least as effective as UFH in treatment of acute coronary syndromes
• Glycoprotein IIb/IIIa inhibitors
• Direct thrombin inhibitors—bivalirudin if history of heparin-induced thrombocytopenia

MEDICATION

• Aspirin: 162–325 mg PO nonenteric coated
• Enoxaparin (Lovenox): 1 mg/kg SC q12h
• Clopidogrel (Plavix): 300–600 mg PO load, 75 mg PO per day
• Prasugrel 60 mg PO load, 10 mg PO per day
• Not to be used in patients with history of stroke
• Ticagrelor 180 mg PO load, 90 mg PO BID
• Glycoprotein IIb/IIIa inhibitor:
  • Abciximab (ReoPro): For use before PCI only; 0.25 mg/kg IV bolus; 0.125 µg/kg/min to a max. of 10 µg/min for 12 hr
  • Eptifibatide (Integrilin): 180 µg/kg IV over 1–2 min, followed by continuous IV infusion of 2 µg/kg/min up to 72 hr
  • Tirofiban (Aggrastat): 0.4 µg/kg/min for 30 min, then 0.1 µg/kg/min for 48–108 hr
• Heparin 60 U/kg IV bolus (max. 4,000 U), then 12 U/kg/h (max. 1,000 U/h)
• Bivalirudin 0.1 mg/kg bolus, followed by 0.25 mg/kg/h for UA/NSTEMI and 0.75 mg/kg bolus, followed by 1.75 mg/kg/h in STEMI
• Metoprolol: 5 mg IV q2min for 3 doses followed by 25–50 mg PO starting dose as tolerated (note: β-blockers contraindicated in cocaine chest pain)
• Fibrinolytics:
  • Recombinant tissue plasminogen activator (Reteplase): 10 U IV bolus, repeat dose after 30 min; patients should also receive heparin 5,000 IU IV bolus, then infuse 1,000 IU/h for 48 hr, keeping activated partial thromboplastin time (aPTT) 1.5–2.5.
  • Streptokinase: 1.5 million U over 60 min; patients should also receive methylprednisolone 250 mg IV.
  • Tissue plasminogen activator: 15 mg IV bolus, then 0.75 mg/kg (max. 50 mg) over 30 min, then 0.5 mg/kg (max. 35 mg) over 60 min; patients should also receive heparin 5,000 IU IV bolus, then infuse 1,000 IU/h for 48 hr keeping a PTT 1.5–2.5
  • Tenecteplase: Weight-based dosing with max. single dose of 30–50 mg given over 5 sec; IV bolus over 5 sec
  • Contraindications:
    • Active internal bleeding
    • History of cerebrovascular accident in last 6 mo
    • History of a hemorrhagic cerebrovascular accident
    • Recent (within 2 mo) intracranial or intraspinal surgery or trauma
    • Intracranial neoplasm, arteriovenous malformation, or aneurysm
    • Known bleeding diathesis
    • Severe, uncontrolled hypertension
    • Pregnancy
    • Head trauma within last month
    • Trauma or surgery within last 2 wk that may result in closed-space bleed

[Outline]

• PRE-HOSPITAL
• INITIAL STABILIZATION/THERAPY
• ED TREATMENT/PROCEDURES
• MEDICATION

DISPOSITION

Admission Criteria

All patients being considered for reperfusion therapy should be admitted to a cath lab or transferred to a PCI center or admitted to tele bed or an ICU setting

Discharge Criteria

No patient being considered for reperfusion therapy should be discharged home from ED

• Goal of reperfusion therapy is primary PCI within 90 min of 1st medical contact. Transfer to a PCI-capable facility when this window can be accomplished or assess for fibrinolytics if > 120 min for transfer
• Goal of fibrinolytics therapy is a 30 min door-to-needle time if PCI not possible or will be delayed
• Goal of reperfusion in STEMI patients by either fibrinolytics or PCI is the major goal
• PCI should be considered in all post arrest patients along with hypothermia

ICD9

410.90 Acute myocardial infarction, unspecified site, episode of care unspecified

ICD10

I21.3 ST elevation (STEMI) myocardial infarction of unspecified site

[Outline]

• ICD9
• ICD10

• American College of Emergency Physicians; Society for Cardiovascular Angiography and Interventions, O'Gara PT, et al. 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;61:e78–e140. doi:10.1016/j.jacc.2012.11.019.
• Wright RS, Anderson JL, Adams CD, et al. 2011 ACCF/AHA focused update of the Guidelines for the Management of Patients with UA/Non-ST-Elevation Myocardial Infarction (updating the 2007 guideline): A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines developed in collaboration with the American College of Emergency Physicians, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2011;57(19):1920–1959. doi:10.1016/j.jacc.2011.02.009.

See Also (Topic, Algorithm, Electronic Media Element)

Acute Coronary Syndrome: Myocardial Infarction

Shamai A. Grossman

Joshua J. Solano