Acute Coronary Syndromes: STEMI

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, usually following complete atherothrombotic occlusion of a large coronary artery, resulting in transmural ischemia. This is accompanied by release of serum cardiac biomarkers and ST-segment elevation on an electrocardiogram (ECG).

Epidemiology

Incidence
There are >650,000 cases of AMI reported annually in the United States. Early revascularization and AMI management has improved mortality, with a 30-day survival of 95%.

Prevalence
  • Leading cause of morbidity and mortality in the United States
  • ~7.5 million people in the United States are affected by AMI.
  • Prevalence increases with age and is higher in men (5.5%) compared to women (2.9%).

Etiology and Pathophysiology

  • Atherosclerotic coronary artery disease (CAD):
    • Atherosclerotic lesions can be fibrotic, calcified, or lipid laden. Thin-capped atheromas are more likely to rupture, causing atherothrombotic occlusion.
  • Nonatherosclerotic causes:
    • Embolism from either infective vegetations, or thrombi originating within the right atrium across the foramen ovale (“paradoxical”), from the left atrium or from within the left ventricle
    • Spontaneous coronary artery dissection: prevalent in fibromuscular dysplasia (FMD) and in young women
    • Mechanical or iatrogenic obstruction: chest trauma, dissection of the aorta and/or coronary arteries
    • Coronary artery spasm from increased vasomotor tone; anginal variant
    • Arteritis and other etiologies: hematologic causes (disseminated intravascular coagulation [DIC], severe anemia), aortic stenosis, cocaine, IV drug use, severe burns, prolonged hypotension

Risk Factors

Advancing age, hypertension, tobacco use, diabetes mellitus, dyslipidemia, family history of premature onset of CAD, sedentary lifestyle

General Prevention

Smoking cessation/abstinence; healthy diet; weight loss/control; regular physical activity and exercise; control of hypertension, hyperlipidemia, and diabetes mellitus

Commonly Associated Conditions

Abdominal aortic aneurysm, cerebrovascular disease, atherosclerotic peripheral vascular disease

Diagnosis

History

  • Symptoms:
    • 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/or epigastrium
    • Patients with inferior MI may present primarily with abdominal discomfort.
  • Previous history of myocardial ischemia (stable or unstable angina, AMI, 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).
  • Tobacco, alcohol, and/or drug abuse (especially cocaine)

Physical Exam

  • General: restlessness, agitation, hypothermia, fever
  • Neurologic: dizziness, syncope, fatigue, asthenia, disorientation (especially in the elderly)
  • Cardiovascular (CV): dysrhythmia, hypotension, widened pulse pressure, S3 and S4, jugular venous distention (JVD)
  • Respiratory: dyspnea, tachypnea, crackles, rales
  • GI: abdominal pain, nausea, vomiting, hiccups
  • Musculoskeletal: pain in neck, back, shoulders, or upper limbs
  • Skin: cool skin, pallor, diaphoresis

Geriatric Considerations

  • Elderly patients may have an atypical presentation, including silent or unrecognized MI. They may often present with syncope, weakness, shortness of breath, unexplained nausea, epigastric pain, altered mental status, or delirium.
  • Women may present with typical and/or “atypical” symptoms such as fatigue, dyspnea, and malaise.
  • Patients with diabetes mellitus may have fewer and less dramatic chest symptoms.

Differential Diagnosis

Unstable angina, aortic dissection, pulmonary embolism (PE), perforating gastric ulcer, pericarditis, dysrhythmias, gastroesophageal reflux disease (GERD), esophageal spasm, biliary/pancreatic pain, hyperventilation syndrome

Diagnostic Tests & Interpretation

Initial Tests (lab, imaging)
  • 12-lead ECG:
    • ≥1 mm ST elevation in a regional pattern, involving at least two contiguous leads, with or without abnormal Q waves
    • STEMI of posterior wall: ST depression ± tall R waves in V1V2
    • Absence of Q waves represents partial or transient occlusion or early infarction.
    • Consider right-sided and posterior chest leads if inferior MI pattern (examine V3R, V4R, V7V9).
    • In the setting of ventricular pacing or a prior left bundle branch block, the Sgarbossa criteria may be helpful.
  • 2-Dimensional transthoracic echocardiography is useful in evaluating regional wall motion in MI and left ventricular function.
    • Useful in assessing mechanical complications and mural thrombus
  • Once diagnosis is suspected, emergent coronary angiography with PCI is preferred.

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 cTnT elevations 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 AMI to troponin testing.
  • Other pertinent labs: fasting lipid profile, complete blood count (CBC), electrolytes, magnesium, blood urea nitrogen, serum creatinine, glucose, hemoglobin A1C, international normalized ratio (INR) if anticoagulation is contemplated, brain natriuretic peptide (BNP)
  • Gender and minorities considerations
    • It is important to note that women and minorities receive less treatment compared with men and Caucasians.

Pregnancy Considerations
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 the same as in nonpregnant patients.

Diagnostic Procedures/Other
  • High-quality portable chest x-ray; transthoracic and/or transesophageal echocardiography; chest computed tomography angiography (CTA) scan may occasionally be of value acutely in equivocal presentations to evaluate for alternative diagnoses (aortic dissection, PE, ventricular aneurysm).
  • Coronary angiography is the definitive test.

ALERT
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.

Treatment

General Measures

  • See “Medication” for ED management.
  • Following emergent revascularization, admit the patient to the coronary care unit (CCU) or a telemetry unit with continuous ECG monitoring and bed rest, and use:
    • Anxiolytics, if needed; stool softeners
    • Antiarrhythmics as needed for unstable dysrhythmia
    • Deep vein thrombosis (DVT) prophylaxis
    • Dual antiplatelet therapy (DAPT) with continuation of aspirin 81 mg/day with 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), high intensity statin
    • Tight BP control, progressively increased physical activity, smoking cessation/abstinence

Medication

Medication recommendations are based on the 2013 American College of Cardiology (ACC)/American Heart Association (AHA) guideline and 2017 European Society of Cardiology (ESC) guideline (1).

First Line

(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 a total of 3 doses, followed by nitroglycerin IV if ongoing pain and/or hypertension and/or management of pulmonary congestion if no contraindications exist such as 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
    • 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 loading dose 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 loading dose should be given if neither prasugrel nor 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 DAPT is controversial. Standard recommendation is 6–12 months after PCI, depending on bleeding and ischemia risks, but newer generation stents may not require DAPT longer than 1 month.
  • Anticoagulation therapy:
    • Unfractionated heparin (UFH) 70- to 100-U/kg IV bolus
    • Enoxaparin 0.5-mg/kg IV bolus
    • Bivalirudin 0.75-mg/kg IV bolus and then 1.75-mg/kg/hr 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) in the following:
        • Symptom onset of ≤12 hours
        • Symptom onset of ≤12 hours and contraindication to fibrinolytic therapy irrespective of time delay
        • Cardiogenic shock or acute severe heart failure (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.
    • Procedural considerations
      • Routine aspiration thrombectomy is no longer recommended prior to PCI because usefulness and safety are not fully established.
      • PCI of infarct-related artery (IRA) is indicated.
      • Routine revascularization of non-IRA lesions in cardiogenic shock is not recommended during primary PCI.
    • Fibrinolysis
      • If presenting to 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 symptom onset, 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 followed by 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 of 48 hours and preferably duration of admission (up to 8 days) or until revascularization, if performed.
  • 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)
  • IV β-blocker should be considered at the time of presentation, if no contraindications exist (signs of congestive heart failure [CHF], low output state) and systolic blood pressure >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 (spironolactone, eplerenone) is recommended in patients with EF <40% and HF or diabetes, who are already receiving an ACE inhibitor and a BB, if there is no renal failure or hyperkalemia.

Second Line
Long-acting nondihydropyridine calcium channel blocker (CCB) when BB is ineffective or contraindicated and EF is normal; do not use immediate-release nifedipine.

Issues For Referral

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.

Surgery/Other Procedures

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.

Admission, Inpatient, and Nursing Considerations

  • All STEMI patients should be admitted to a CCU or an intensive cardiac care unit for evaluation and treatment.
  • Right ventricular infarction may need fluid resuscitation for hypotension.

Ongoing Care

Follow-up Recommendations

Patient Monitoring
  • STEMI patients should follow up with a cardiologist 1–2 weeks postdischarge, every 3 months for the first year, and then yearly.
  • Emphasize medication adherence and encourage smoking cessation.
  • In patient with left ventricular ejection fraction equal or less than 40%, repeat echocardiography 6–12 weeks after AMI or after complete revascularization, is recommended to assess the potential need for primary prevention implantable cardioverter defibrillator implantation.
  • Consider an exercise-based cardiac rehabilitation program.

Diet

Low-fat/healthy-fat diet: reduced intake of saturated fats (to <7% of total calories) (but dairy fats are possibly not associated with CAD), eliminate trans fatty acids (to <1% of total calories). Impact of low-cholesterol diet remains uncertain. Mediterranean diet is healthy.

Patient Education

May resume sexual activity 1 or more weeks after uncomplicated MI or 6 to 8 weeks after CABG; smoking cessation and low-fat diet

Prognosis

Poor prognosis is associated with advanced age, diabetes, delayed or unsuccessful revascularization, reduced left ventricular systolic function, and evidence of congestive heart failure.

Complications

HF, myocardial wall rupture, left ventricular aneurysm, pericarditis, dysrhythmias, acute mitral regurgitation, and depression (common)

Codes

ICD-10

  • 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

ICD-9

  • 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

SNOMED

  • 394659003 Acute coronary syndrome (disorder)
  • 401303003 Acute ST segment elevation myocardial infarction (disorder)
  • 443502000 Atherosclerosis of coronary artery (disorder)

Clinical Pearls

  • STEMI occurs from occlusion of one or more coronary arteries resulting in transmural myocardial ischemia.
  • Early revascularization with percutaneous coronary intervention (PCI) within 90 minutes of presentation at a PCI capable hospital is required, or within 120 minutes if transfer to a PCI-capable hospital is required.
  • Fibrinolytic therapy should be initiated within 30 minutes if presenting to a hospital without PCI capability and cannot be transferred to a PCI-capable facility to undergo PCI within 120 minutes of first medical contact.
  • Duration of dual antiplatelet therapy should be determined based on an individualized risk assessment of ischemia and bleeding, and also considering type of intervention (PCI, CABG) undertaken.

Authors


Yutthapong Temtanakitpaisan, MD
Adedotun Anthony Ogunsua, MD, MPH
Kimberly Atianzar, MD

Bibliography

  1. Ibanez B, James S, Agewall S, et al. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force for the management of acute myocardial infarction in patients presenting with ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J. 2018;39(2):119–177.  [PMID:23247303]


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