Acute Coronary Syndromes: STEMI
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 complete 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-segment elevation on an ECG.
In 2009, ~683,000 patients were discharged from U.S. hospitals diagnosed with acute coronary syndrome (ACS). STEMI comprises about 25–40% of MI presentations.
- 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)
- Atherosclerotic lesions can be fibrotic, calcified, or lipid laden. Thin-capped atheroma are more likely to rupture and result in thrombotic occlusion.
- Emboli: vegetation, 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
Advancing age, hypertension, tobacco use, diabetes mellitus, dyslipidemia, family history of premature onset of CAD, sedentary lifestyle
Smoking cessation, healthy diet, weight control, regular physical activity, control of hypertension, hyperlipidemia, and diabetes
Commonly Associated Conditions
Abdominal aortic aneurysm, extracranial cerebrovascular (CV) disease, atherosclerotic peripheral vascular disease
- Classically, sudden onset of chest heaviness/tightness, with or without exertion, lasting minutes to hours
- Pain/discomfort radiating to neck, jaw, interscapular area, upper extremities, and epigastrium
- Previous history of myocardial ischemia (stable or unstable angina, MI, coronary bypass surgery, or percutaneous coronary intervention [PCI])
- Assess risk factors for CAD, history of bleeding, noncardiac surgery, family history of premature CAD.
- Medications: Ask if recent use of phosphodiesterase type 5 inhibitors (if recent use, avoid concomitant nitrates).
- Alcohol and drug abuse (especially cocaine)
- General: restless, agitated, hypothermia, fever
- Neurologic: dizziness, syncope, fatigue, asthenia, disorientation (especially in the elderly)
- 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
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.
Unstable angina, aortic dissection, pulmonary embolism (PE), perforating ulcer, pericarditis, dysrhythmias, gastroesophageal reflux disease (GERD) and spasm, biliary/pancreatic pain, hyperventilation syndrome
Diagnostic Tests & InterpretationInitial Tests (lab, imaging)
- 12-lead ECG: ST-segment elevation in a regional pattern ≥1 mm ST elevation (at least two contiguous leads), 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, V7V9).
- ECG with continuous monitoring
- 2D and M-mode echocardiographies are 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
- Once diagnosis suspected, coronary angiography is preferred emergently, with PCI.
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-MB (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; hemoglobin A1C; international normalized ratio (INR) if anticoagulation contemplated; brain natriuretic peptide (BNP) is elevated in acute MI; may or may not indicate heart failure
Pregnant patients presenting with STEMI will need discussion of risks and benefits of invasive coronary angiography with radiation exposure to fetus. Management should otherwise be same as in nonpregnant patients, with emergent coronary angiography and PCI.
High-quality portable chest x-ray; transthoracic and/or transesophageal echocardiography, contrast chest CT scan may occasionally be of value acutely in equivocal presentations to evaluate for alternative diagnoses (aortic dissection, PE, ventricular aneurysm). Coronary angiography is definitive test.
Patients with chronic kidney disease need special attention to amount of contrast media used. Reduced volume of contrast and use of low or isosmolar contrast media may lower risk of progression of renal impairment.
Thrombotic occlusion of coronary artery seen on coronary angiography
- Following emergent revascularization, 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, β-blocker (BB), ACE inhibitors (or ARB if ACE-intolerant), lipid-lowering therapy, tight BP control, progressively increased physical activity, smoking cessation
- 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.
(While awaiting revascularization)
- Supplemental oxygen 2 to 4 L/min for patients with 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 or vardenafil within 24 hours or within 48 hours of tadalafil)
- Morphine sulfate 4 to 8 mg IV with 2 to 8 mg IV repeated at 5- to 15-minute intervals to relieve pain, anxiety, or pulmonary congestion
- Antiplatelet agents
- Aspirin (ASA), non–enteric-coated, initial dose 162 to 325 mg chewed (1)[A]
- A loading dose of a P2Y12 inhibitor is recommended for patients with STEMI for whom PCI is planned. Prasugrel or ticagrelor is preferred.
- Prasugrel 60 mg should be given as soon as possible for primary PCI. Prasugrel is contraindicated in patients with previous stroke/transient ischemic attack. Do not recommend in patients aged >75 years or lower body weight (<60 kg).
- Ticagrelor 180 mg loading dose. Ticagrelor may cause transient dyspnea.
- Clopidogrel 600 mg should be given if neither prasugrel or ticagrelor is available.
- Cangrelor may be considered in patients not pretreated with oral P2Y12 receptor inhibitors at the time of PCI or in those who are unable to take oral agents.
- Duration of dual antiplatelet therapy (DAPT) is recommended 12 months after PCI. In patients who are at high risk of severe bleeding complications, a P2Y12 inhibitor may be discontinued after 6 months; anticoagulation therapy
- Unfractionated heparin (UFH) 50- to 70-U/kg IV bolus
- Enoxaparin 0.5-mg/kg IV bolus
- Bivalirudin 0.75-mg/kg IV bolus and then 1.75-mg/kg/h infusion for up to 4 hours after procedure
- 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
- Radial access is recommended over femoral access.
- Primary PCI (balloon angioplasty, coronary stents)
- Procedural considerations
- Routine aspiration thrombectomy no longer recommended prior to PCI as usefulness and safety not fully established (3)[C]
- PCI of infarct-related artery (IRA) is indicated.
- PCI of a noninfarct artery may be considered in selected patients with STEMI and multivessel disease who are hemodynamically stable, either at the time of primary PCI or as a planned staged procedure.
- If presenting at a hospital without PCI capability and cannot be transferred to a PCI-capable facility to undergo PCI within 120 minutes of first medical contact
- If no contraindications, administer within 12 to 24 hours of onset of symptoms if there is evidence of ongoing ischemia.
- Alteplase (tPA): 15-mg IV bolus, followed by 0.75 mg/kg (up to 50 mg) IV over 30 minutes and then 0.5 mg/kg (up to 35 mg) over 60 minutes; maximum 100 mg over 90 minutes
- Reteplase (rPA): 10 units IV bolus; give second bolus 30 minutes apart.
- Tenecteplase (TNK-tPA): 30- to 50-mg (based on weight) IV bolus. Recommend to reduce to half dose in patients ≥75 years of age.
- Adjunctive antiplatelet therapy with fibrinolysis
- Aspirin (162- to 325-mg loading dose and then 81 mg daily) indefinitely
- Clopidogrel (300-mg loading dose for patients <75 years of age, 75-mg dose for patients >75 years of age). Clopidogrel 75 mg daily should be continued for at least 14 days and up to 1 year.
- Adjunctive anticoagulation therapy with fibrinolysis
- Use anticoagulants (UFH, enoxaparin, or fondaparinux) as ancillary therapy to reperfusion therapy for minimum 48 hours and preferably duration of admission (up to 8 days) or until revascularization, if performed.
- Coronary reperfusion therapy
- Glycoprotein IIb/IIIa receptor antagonists at time of primary PCI in selected patients if there is no reflow or thrombotic complications (abciximab, eptifibatide, or tirofiban)
- Intravenous BB should be considered at the time of presentation, if no contraindications exist (signs of congestive heart failure [CHF], low output state) and SBP >120 mm Hg.
- ACE inhibitors should be initiated orally within 24 hours of STEMI in patients with anterior infarction, HF, diabetes, or ejection fraction (EF) ≤0.40 unless contraindicated.
- High-intensity statin therapy should be started as early as possible.
- Mineralocorticoid receptor antagonist is recommended in patients with EF <40% and heart failure or diabetes, who are already receiving an ACE inhibitor and a BB, if there is no renal failure or hyperkalemia.
Long-acting nondihydropyridine calcium channel blocker (CCB) when BB is ineffective or contraindicated if EF is normal; do not use immediate-release nifedipine.
Urgent coronary artery bypass graft (CABG) surgery is indicated in patients with STEMI and coronary anatomy not amenable to PCI who have ongoing or recurrent ischemia, cardiogenic shock, severe HF, or other high-risk features.
- All patients with STEMI should be admitted to a CCU or intensive cardiac care unit 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.
- Right ventricular infarction may need fluid resuscitation for hypotension.
Emphasize medication adherence. Identify high-risk patients for implantable cardioverter defibrillator (ICD) placement (especially those with EF <30%). Consider exercise-based cardiac rehabilitation program and encourage smoking cessation.
Low-fat diet: reduced intake of saturated fats (to <7% of total calories) (but dairy fats are not likely associated with CAD), trans fatty acids (to <1% of total calories). Impact of low-cholesterol diet remains uncertain.
May resume sexual activity 1 or more weeks after uncomplicated MI or 6 to 8 weeks after CABG; smoking cessation and low-fat diet
Heart failure, myocardial rupture/left ventricular aneurysm, pericarditis, dysrhythmias, acute mitral regurgitation, and depression (common)
- I21.3 ST elevation (STEMI) myocardial infarction of unspecified site
- I24.9 Acute ischemic heart disease, unspecified
- I25.10 Athscl heart disease of native coronary artery w/o ang pctrs
- 410.90 Acute myocardial infarction of unspecified site, episode of care unspecified
- 411.1 Intermediate coronary syndrome
- 414.01 Coronary atherosclerosis of native coronary artery
- 394659003 Acute coronary syndrome (disorder)
- 401303003 Acute ST segment elevation myocardial infarction (disorder)
- 443502000 Atherosclerosis of coronary artery (disorder)
For elective surgeries in patients on DAPT, it is recommended to wait until completion of mandatory regime and continue ASA perioperatively.
Hambik Tankazyan, DO
Yutthapong Temtanakitpaisan, MD
Daniel Z. Fisher, MD
- O’Gara PT, Kushner FG, Ascheim DD, et al; for CF/AHA Task Force. 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. [PMID:23247303]
- Ibánez B, James S, Agewall S, et al. 2017 ESC guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation. Rev Esp Cardiol (Engl Ed). 2017;70(12):1082. [PMID:29198432]
- Levine GN, Bates ER, Blankenship JC, et al. 2015 ACC/AHA/SCAI focused update on primary percutaneous coronary intervention for patients with ST-elevation myocardial infarction: an update of the 2011 ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention and the 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction. J Am Coll Cardiol. 2016;67(10):1235–1250. [PMID:26498666]
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