> Table of Contents > Acute Coronary Syndromes: Stemi
Acute Coronary Syndromes: Stemi
Kassie S. Johnson, MD
Fozia Akhtar Ali, MD
image BASICS
DESCRIPTION
Acute myocardial infarction (AMI) is the rapid development of myocardial necrosis resulting from a sustained and complete absence of blood flow to a portion of the myocardium. ST-segment elevation myocardial infarction (STEMI) occurs when coronary blood flow ceases following thrombotic occlusion of a large coronary artery (usually) affected by atherosclerosis, causing transmural ischemia. This is accompanied by release of serum cardiac biomarkers and ST elevation (and likely a Q wave when infarction develops) on an ECG.
EPIDEMIOLOGY
Incidence
In the United States, estimated annual incidence of MI is 600,000 new and 320,000 recurrent attacks. In 2009, ˜683,000 patients were discharged from United States hospitals diagnosed with acute coronary syndromes (ACS).
Prevalence
  • Leading cause of morbidity and mortality in the United States
  • ˜7.5 million people in the United States are affected by MI.
  • Prevalence increases with age and is higher in men (5.5%) than in women (2.9%).
ETIOLOGY AND PATHOPHYSIOLOGY
  • Atherosclerotic coronary artery disease (CAD)
  • Nonatherosclerotic
    • Emboli: for example, thrombi from left ventricle or atrium
    • Mechanical obstruction: chest trauma, dissection of aorta or coronary arteries
    • Increased vasomotor tone, variant angina
    • Arteritis, others: hematologic (disseminated intravascular coagulation [DIC]), aortic stenosis, cocaine, IV drug use, severe burns, prolonged hypotension
  • Atherosclerotic lesions may be smooth and concentric or rough, eccentric, and fissured. Plaques that are rough and eccentric are more unstable, thrombogenic, and prone to rupture.
RISK FACTORS
Advancing age, hypertension, tobacco use, diabetes mellitus, dyslipidemia, family history of premature onset of CAD, sedentary lifestyle
GENERAL PREVENTION
Smoking cessation, healthy diet, weight control, regular physical activity, maintain goal blood pressure
COMMONLY ASSOCIATED CONDITIONS
Abdominal aortic aneurysm, extracranial cerebrovascular disease, atherosclerotic peripheral vascular disease
image DIAGNOSIS
PHYSICAL EXAM
  • General: restless, agitated, hypothermia, fever
  • Neurologic: dizziness, syncope, fatigue, asthenia, disorientation (especially in the elderly)
  • Cerebrovascular (CV): dysrhythmia, hypotension, widened pulse pressure, S3 and S4, jugular venous distention (JVD)
  • Respiratory: dyspnea, tachypnea, crackles
  • GI: abdominal pain, nausea, vomiting
  • Musculoskeletal: pain in neck, back, shoulder, or upper limbs
  • Skin: cool skin, pallor, diaphoresis
Geriatric Considerations
Elderly patients may have an atypical presentation, including silent or unrecognized MI, often with complaints of syncope, weakness, shortness of breath, unexplained nausea, epigastric pain, altered mental status, delirium. Patients with diabetes mellitus may have fewer and less dramatic chest symptoms.
DIFFERENTIAL DIAGNOSIS
Unstable angina, aortic dissection, pulmonary embolism (PE), perforating ulcer, pericarditis, dysrhythmias, gastroesophageal reflux disease (GERD) and spasm, biliary/pancreatic pain, hyperventilation syndrome
DIAGNOSTIC TESTS & INTERPRETATION
  • Symptoms of ischemia
  • New significant ST/T wave changes or left bundle branch block (LBBB)
  • Pathologic Q waves on ECG
  • New loss of viable myocardium or regional wall motion abnormality, as observed on imaging
  • Intracoronary thrombus diagnosed by angiography or autopsy
Initial Tests (lab, imaging)
  • Coronary angiography with measurement of fractional flow reserve (FFR)
  • 12-lead ECG: ST-segment elevation in a regional pattern ≥ 1 mm ST elevation, with or without abnormal Q waves. ST depression ± tall R wave in V1/V2 may be STEMI of posterior wall. Absence of Q waves represents partial or transient occlusion or early infarction. New ST- or T-wave changes indicative of myocardial ischemia or injury. Consider right-sided and posterior chest leads if inferior MI pattern (examine V3R, V4R, V7-V9).
  • ECG with continuous monitoring
    • 2D and M-mode echocardiography is useful in evaluating regional wall motion in MI and left ventricular function.
    • Portable echo can clarify diagnosis of STEMI if concomitant LBBB.
    • Useful in assessing mechanical complications and mural thrombus
Follow-Up Tests & Special Considerations
  • Serum biomarkers
    • Troponin I and T (cTnI, cTnT) rise 3 to 6 hours after onset of ischemic symptoms.
    • Elevations in cTnI persist for 7 to 10 days, whereas those in cTnT persist for 10 to 14 days after MI.
    • Myoglobin fraction of creatine kinase (CK-MB): rises 3 to 4 hours after onset of myocardial injury; peaks at 12 to 24 hours and remains elevated for 2 to 3 days; CK-MB adds little diagnostic value in assessment of possible ACS to troponin testing.
    • Myoglobin: early marker for myocardial necrosis; rises 2 hours after onset of myocardial necrosis, reaches peak at 1 to 4 hours, and remains elevated for 24 hours; myoglobin adds little diagnostic value in assessment of possible ACS to troponin testing.
  • Fasting lipid profile, CBC with platelets, electrolytes, magnesium, BUN, serum creatinine, and glucose; international normalized ratio (INR) if anticoagulation contemplated; brain natriuretic peptide (BNP) is elevated in acute MI; may or may not indicate heart failure
Pregnancy Considerations
Findings mimicking acute MI in pregnancy: ST-segment depression after anesthesia, increase in CK-MB after delivery, and mild increase in troponin I levels in preeclampsia and gestational hypertension
Diagnostic Procedures/Other
High-quality portable chest x-ray; transthoracic and/or transesophageal echocardiography, contrast chest CT scan, or MRI may occasionally be of value acutely. Coronary angiography is definitive test.
Test Interpretation
Myocardial necrosis and atherosclerosis, if etiologic
image TREATMENT
GENERAL MEASURES
  • Admit to telemetry/coronary care unit (CCU) with continuous ECG monitoring and bed rest. Anxiolytics, if needed; stool softeners
  • Antiarrhythmics, as needed, for unstable dysrhythmia; deep vein thrombosis (DVT) prophylaxis
  • Continuation of aspirin 81 mg/day and clopidogrel 75 mg/day or prasugrel 10 mg/day or ticagrelor 90 mg twice daily, BB, ACE inhibitors (or ARB if ACE-intolerant), lipid-lowering therapy, tight BP control, progressively increased physical activity, smoking cessation, annual influenza vaccine
  • P.19

  • Assess for depression, and treat with an SSRI or psychotherapy if present, as depression is present in 20% of patients post-MI and is a potent predictor for poor prognosis. Although it is unclear yet if treatment improves mortality, it does improve quality of life.
MEDICATION
Medication recommendations based on 2009 ACC/AHA (1) focused guideline updates [A] and [B] level recommendations and 2012 ESC STEMI guidelines (2)[A,B]
First Line
  • Supplemental oxygen 2 to 4 L/min for patients with arterial oxygen saturation <90% or respiratory distress
  • Nitroglycerin (NTG) sublingual 0.4 mg q5min for total of 3 doses, followed by nitroglycerin IV if ongoing pain and/or hypertension and/or management of pulmonary congestion if no contraindications exist (systolic <90 mm Hg or 30 mm Hg below baseline, right ventricle (RV) infarct, use of sildenafil within 24 hours or within 48 hours of tadalafil)
  • Morphine sulfate 2 to 4 mg IV with increments of 2 to 8 mg IV repeated at 5- to 15-minute intervals to relieve pain or pulmonary congestion
  • Antiplatelet agents
    • Aspirin (ASA), non-enteric-coated, initial dose 162 to 325 mg chewed (1)[A]
    • A loading dose of a thienopyridine is recommended for patients with STEMI for whom PCI is planned.
      • 600 mg of clopidogrel should be given as early as possible before or at the time of primary or nonprimary PCI.
      • Prasugrel 60 mg should be given as soon as possible for primary PCI. Do not use in patients likely to undergo coronary artery bypass graft (CABG) or with active bleeding, history of transient ischemic attack (TIA) or stroke, or additional risk factors for bleeding (body weight <60 kg or concomitant use of medications that increase risk of bleeding). (Generally, not recommended for patients age ≥75 years.)
      • Ticagrelor 180 mg loading dose
      • Duration of therapy with a thienopyridine varies. At least 12 months for patients receiving drugeluting stent (DES) during PCI for ACS and up to 12 months for patients receiving bare-metal stent (BMS). Consider earlier discontinuation if risk of morbidity due to bleeding outweighs the benefits of therapy. Discontinue clopidogrel for at least 5 days or prasugrel at least 7 days prior to planned CABG. Management of patients on dual antiplatelet therapy (DAPT) who are referred for surgical procedures depends on the level of emergency and the thrombotic and bleeding risk of the individual patient.
    • For patients with STEMI undergoing nonprimary PCI
      • Continue clopidogrel in a patient who has received fibrinolytic therapy and has been given clopidogrel.
      • Administer loading dose of clopidogrel 600 mg if patient received a fibrinolytic without a thienopyridine or ticagrelor 180 mg or once the coronary anatomy is known and PCI is planned; administer a loading dose of prasugrel as soon as possible but not later than 1 hour after PCI. Administer loading dose of clopidogrel 300 mg in patients <75 years of age who received fibrinolytic therapy or who did not receive reperfusion therapy.
      • Clopidogrel 75 mg should be given with aspirin in patients with STEMI regardless of reperfusion therapy.
  • β-blocker (BB) within 24 hours, if no contraindications exist (signs of congestive heart failure [CHF], low output state)
  • Glycoprotein IIb/IIIa receptor antagonists at time of primary PCI in selected patients: abciximab, eptifibatide, or tirofiban
  • ACE inhibitors should be initiated orally within 24 hours of STEMI in patients with anterior infarction, HF, or ejection fraction (EF ≤0.40) unless contraindicated.
PCI versus fibrinolysis: goal is to keep total ischemic time within 120 minutes. Door to needle time should be within 30 minutes or door to balloon time within 90 minutes.
  • Coronary reperfusion therapy
    • Primary PCI (balloon angioplasty, coronary stents)
      • Symptom onset of ≤ 12 hours
      • Symptom onset of ≤ 12 hours and contraindication to fibrinolytic therapy irrespective of time delay
      • Cardiogenic shock or acute severe HF irrespective of time delay from onset of MI
      • Evidence of ongoing ischemia 12 to 24 hours after symptom onset
      • If substantial risk for intracranial hemorrhage (ICH)
      • Age <75 years with STEMI or LBBB who develop shock within 36 hours of AMI
  • Fibrinolysis
    • If EMS has fibrinolytic capability and the patient qualifies for therapy, prehospital fibrinolysis should be started within 30 minutes of EMS arrival on scene.
    • If presenting at a hospital without PCI capability and cannot be transferred to a PCI-capable facility to undergo PCI within 90 minutes of first medical contact
    • If no contraindications, administer within 12 hours, but not beyond 24 hours of onset of symptoms to patients with STEMI in ≥ 2 contiguous leads and/or new or presumably new LBBB.
      • Alteplase (rt-PA): 15-mg IV bolus, followed by 0.75 mg/kg (up to 50 mg) IV over 30 minutes, then 0.5 mg/kg (up to 35 mg) over 60 minutes; maximum 100 mg over 90 minutes
      • Reteplase (r-PA): 10 units IV bolus over 2 minutes, give 2nd bolus 30 minutes later.
      • Tenecteplase (TNK-tPA): 30 to 50 mg (based on weight) IV bolus over 5 to 10 seconds
    • Combination reperfusion with abciximab and half-dose r-PA or TNK-tPA
    • Use anticoagulants (unfractionated heparin [UFH], enoxaparin, or fondaparinux) as ancillary therapy to reperfusion therapy for minimum 48 hours and duration of admission (up to 8 days). Avoid UFH if >48 hours of anticoagulant required. Recommend supportive anticoagulant regimens in patients proceeding to primary PCI who have been treated with ASA and thienopyridine. Administer additional boluses of UFH as needed to maintain therapeutic clotting time levels in patients who received prior treatment with UFH. Bivalirudin recommended as a supportive measure for primary PCI in patients with or without prior treatment with UFH.
Second Line
  • Long-acting nondihydropyridine calcium channel blocker (CCB) when BB is ineffective or contraindicated if EF is normal; do not use of immediate release nifedipine
  • See chapter on “Heart Failure, Chronic” for additional medication management.
SURGERY/OTHER PROCEDURES
Intra-aortic balloon pump for cardiogenic shock; PCI of the left main coronary artery with stents as an alternative to CABG in patients with favorable anatomy and comorbid conditions that may increase risk of adverse surgical outcomes if CABG chosen
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
All patients with STEMI should be admitted to a CCU for evaluation and treatment. Transfer high-risk patients who receive fibrinolytic therapy as primary reperfusion therapy at a non-PCI-capable facility to a PCI-capable facility as soon as possible. Also admit suspected acute MI, ACS/positive cardiac markers or ST deviations, and hemodynamic abnormalities.
IV Fluids
Right ventricular infarction may need fluid resuscitation for hypotension.
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Follow up in 3 to 6 weeks of discharge. Identify highrisk patients for implantable cardioverter defibrillator (ICD) placement (especially those with EF <30%). Consider exercise-based cardiac rehabilitation program.
DIET
NPO for first 4 to 12 hours due to risk of emesis or aspiration
PATIENT EDUCATION
May resume sexual activity within 10 days, consistent with current exercise capacity. Driving can resume 1 week after discharge. Low-fat diet
REFERENCES
1. O'Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2013;127(4):529-555.
2. Steg PG, James SK, Atar D, et al. ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation. Eur Heart J. 2012;33(20):2569-2619.
Codes
ICD10
  • I24.9 Acute ischemic heart disease, unspecified
  • I21.3 ST elevation (STEMI) myocardial infarction of unspecified site
  • I25.10 Athscl heart disease of native coronary artery w/o ang pctrs
Clinical Pearls
  • Discontinue clopidogrel at least 5 to 7 days before elective CABG.
  • For elective surgeries in patients on dual antiplatelet therapy (DAPT), it is recommended to wait until completion of mandatory regime and continue ASA perioperatively.