Myocardial Infarction, ST-Segment Elevation (STEMI) – Causes, Symptoms, Diagnosis, Treatment and Ongoing care

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 coronary artery 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 occurs) on an electrocardiogram (ECG).

Epidemiology

Incidence

In the US, estimated annual incidence of MI is 600,000 new and 320,000 recurrent attacks.

Prevalence

Leading cause of morbidity and mortality in the USApproximately 7.5 million people in the US are affected by MI.Prevalence increases with age and is higher in men (5.5%) than women (2.9%).

Risk Factors

Advancing age, hypertension, tobacco use, diabetes mellitus, dyslipidemia, family history of premature onset of coronary artery disease (CAD), sedentary lifestyle

General Prevention

Smoking cessation, consume healthy diet, weight control, regular physical activity, maintain goal blood pressure

Pathophysiology

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.

Etiology

Atherosclerotic coronary artery diseaseNonatherosclerotic: Emboli: For example, thrombi from left ventricle or atriumMechanical obstruction: Chest trauma, dissection of aorta or coronary arteriesIncreased vasomotor tone, variant anginaArteritis, others: Hematologic (DIC), aortic stenosis, cocaine, intravenous (IV) drug use, severe burns, prolonged hypotension

Commonly Associated Conditions

Abdominal aortic aneurysm, extracranial cerebrovascular disease, atherosclerotic peripheral vascular disease

Diagnosis

History

Classically, sudden-onset chest heaviness/tightness, with or without exertion, lasting at least minutesPain or discomfort radiating to neck, jaw, interscapular area, upper extremities, and epigastriumPrevious 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 CADMedications: Phosphodiesterase-5 inhibitors (if recent use, avoid concomitant nitrates)Alcohol and drug abuse (especially cocaine)

Physical Exam

General: Restless, agitated, hypothermia, feverNeuro: 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, cracklesGastrointestinal (GI): Abdominal pain, nausea, vomitingMusculoskeletal: Pain in neck, back, shoulder, or upper limbsSkin: 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, or dementia. Patients with diabetes mellitus may have fewer and less dramatic chest symptoms.

Diagnostic Tests & Interpretation

Lab

Initial lab tests

12-lead electrocardiogram (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 represent 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 (V3R, V4R, V7-V9).

Follow-Up & Special Considerations

Serum biomarkers: Troponin I and T (cTnI, cTnT) rise 3–6 hours after onset of ischemic symptoms. Elevations in cTnI persist for 7–10 days, while those in cTnT persist for 10–14 days after MI.Myoglobin fraction of creatine kinase (CK-MB): Rises 3–4 hours after onset of myocardial injury; peaks at 12–24 hours and remains elevated for 2–3 daysMyoglobin: Early marker for myocardial necrosis. Rises 2 hours after onset of myocardial necrosis, reaches peak at 1–4 hours, and remains elevated for 24 hours.Fasting lipid profile, complete blood count with platelets, electrolytes, magnesium, blood urea nitrogen (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

Imaging

Initial approach

ECG with continuous monitoring:

2-D 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 left bundle branch block (LBBB).Useful in assessing mechanical complications and mural thrombus

Diagnostic Procedures/Surgery

Coronary pressure (fractional flow reserve) or Doppler velocimetry to determine whether PCI of a specific coronary lesion is warranted. High-quality portable chest x-ray.Transthoracic and/or transesophageal echocardiography, contrast chest computed tomography (CT) scan, or magnetic resonance imaging (MRI). Coronary angiography.

Alert

Isosmolar contrast medium or low-molecular-weight contrast medium other than ioxaglate or iohexol is indicated in patients with chronic kidney disease undergoing angiography who are not undergoing chronic dialysis.

Pathological Findings

Myocardial necrosis and atherosclerosis, if etiologic

Differential Diagnosis

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

Treatment

Medication

Medication recommendations based upon 2009 ACC/AHA focused guideline updates (1)

First Line

Supplemental oxygen 2–4 L/min, maintaining arterial oxygen saturation >90%Nitroglycerin (NTG) sublingual 0.4 mg every 5 mins for total of 3 doses, followed by nitroglycerin IV if ongoing pain and/or hypertension and/or management of pulmonary congestionMorphine sulfate 2–4 mg IV (with increments of 2–8 mg IV repeated at 5–15-minute intervals to relieve pain or pulmonary congestion associated with STEMIAntiplatelet agents: Aspirin (ASA), nonenteric-coated, initial dose 162 mg to 325 mg chewedA loading dose of a thienopyridine is recommended for STEMI patients for whom PCI is planned:At least 300–600 mg of clopidogrel should be given as early as possible before or at the time of primary or nonprimary PCI orPrasugrel 60 mg should be given as soon as possible for primary PCI. Not recommended as part of a dual-antiplatelet therapy regimen in STEMI patients with prior history of stroke and transient ischemic attack for whom primary PCI is planned.Duration of therapy with a thienopyridine varies. 12 months for patients receiving drug eluting stent (DES) during PCI for ACS. Consider earlier discontinuation if risk of morbidity due to bleeding outweighs the benefits of therapy. May continue clopidogrel or prasugrel for longer than 15 months in patients undergoing DES placement. Discontinue clopidogrel for at least 5 days or prasugrel at least 7 days prior to planned CABG.For STEMI patients undergoing nonprimary PCI: Continue clopidogrel in a patient who has received fibrinolytic therapy and has been given clopidogrel.Administer loading dose of clopidogrel 300–600 mg if patient received a fibrinolytic without a thienopyridine, or, once the coronary anatomy is known and PCI is planned, administer a loading dose of prasugrel as soon as possible, but no later than 1 hour after PCI. Administer loading dose of clopidogrel 300 mg in patients less than 75 years of age who received fibrinolytic therapy or who do not receive reperfusion therapy.Clopidogrel 75 mg should be given with aspirin in patients with STEMI regardless of reperfusion therapy. Clopidogrel treatment should continue for at least 14 days.Beta-blocker (BB) within 24 hours, if no contraindications existGlycoprotein IIb/IIIa receptor antagonists at time of primary PCI in selected patients: Abciximab, eptifibatide, or tirofibanAngiotensin-converting enzyme (ACE) inhibitors should be initiated orally within the first 24 hours of STEMI in patients with anterior infarction or LVEF less than 0.40 in the absence of contraindications. Initiate ACE inhibitors within 24 hours of STEMI in all patients if no contraindications exist.Coronary reperfusion therapy: Primary PCI: If patient presents within 12 hours of symptom onset and “door-to-balloon inflation” within 90 minutes of presentation at a facility with PCI capabilityIf substantial risk for intracranial hemorrhage (ICH)Age <75 with STEMI or LBBB who develop shock within 36 hours of acute MI (AMI)Severe congestive heart failure and/or pulmonary edema (Killip class III)Not eligible to receive fibrinolytic therapy within 12 hours of onset of symptomsPatients with onset of symptoms within the prior 12–24 hours and 1 or more of the following: Severe CHF, hemodynamis or electrical instability, or persistent ischemic symptomsFibrinolysis: 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, administer fibrinolytic therapy, “door-to-needle,” within 30 minutes of presentation.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 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 mins, then 0.5 mg/kg (up to 35 mg) over 60 min; max 100 mg over 90 minReteplase (r-PA): 10 units IV bolus over 2 min, give 2nd bolus 30 min laterTenecteplase (TNK-tPA): 30–50 mg (based on weight) IV bolus over 5–10 secsCombination reperfusion with abciximab and half-dose r-PA or TNK-tPAUse 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 beta-blocker (BB) is ineffective or contraindicated if ejection fraction (EF) is normalAldosterone receptor antagonist if already receiving therapeutic doses of an ACE inhibitor and beta-blocker. Caution re: hyperkalemia. Use low dose of aldosterone antagonist (e.g., spironolactone 25 mg daily).Lipid-lowering therapy: Statin (preferred because of additional nonlipid effects on vascular function), niacin, or fibrate

Additional Treatment

General Measures

Admit to telemetry/coronary care unit 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, clopidogrel, BB, ACE inhibitors (or ARB if ACE-intolerant), lipid-lowering therapy, tight blood pressure control, progressively increased physical activity, smoking cessation, annual influenza vaccineElicit symptoms or signs of depression and treat with a selective serotonin reuptake inhibitor (SSRI) or psychotherapy if present.

Issues for Referral

Cardiac rehabilitation, neurology/neurosurgery if intracranial hemorrhage

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 comorbidities that may increase risk of adverse surgical outcomes if CABG chosen. Coronary artery bypass graft (CABG) surgery.

In-Patient Considerations

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.

Admission Criteria

Definitive or suspected acute MI, ongoing pain, positive cardiac markers, ST deviations, hemodynamic abnormalities

IV Fluids

Right ventricular infarction may need fluid resuscitation for hypotension.

Ongoing Care

Follow-Up Recommendations

F/U w-in 3–6 weeks of d/c. Identify high-risk patients for implantable cardioverter defibrillator (ICD) placement (especially those with EF <30%).

Diet

n.p.o. for first 4–12 hours due to risk of emesis or aspiration; request dietary consult if lipid, weight, or glucose issues

Patient Education

May resume sexual activity within 7–10 days, consistent with current exercise capacity. Driving can resume 1 week after discharge when in compliance with individual state laws. Recommend diet low in saturated fats and cholesterol.

Complications

Heart failure, myocardial rupture/left ventricular aneurysm, pericarditis, dysrhythmias, acute mitral regurgitation, severe depression (common)

References

1. Kushner FG, et al. 2009 focused updates: ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction and ACC/AHA/SCAI guidelines on percutaneous coronary intervention.J Am Coll Cardiol. 2009;54:2205–41.

Codes

ICD9

410.90 Acute myocardial infarction of unspecified site, episode of care unspecified410.91 Acute myocardial infarction of unspecified site, initial episode of care410.92 Acute myocardial infarction of unspecified site, subsequent episode of care

Snomed

22298006 Myocardial infarction (disorder)401303003 Acute ST segment elevation myocardial infarction (disorder)

Clinical Pearls

Discontinue clopidogrel at least 5–7 days before elective CABG. Do not administer nitrates to patients who have recently used PDE-5 inhibitors.