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Key Features

Essentials of Diagnosis

  • Sudden but not instantaneous development of prolonged (> 30 minutes) anterior chest discomfort (sometimes felt as "gas" or pressure)

  • Sometimes painless, masquerading as acute heart failure (HF), syncope, stroke, or shock

  • ECG: ST-segment elevation myocardial infarction (STEMI) or left bundle branch block

  • Immediate reperfusion treatment is warranted

    • Primary percutaneous coronary intervention (PCI) within 90 minutes of first medical contact is the goal and is superior to fibrinolytic therapy

    • Fibrinolytic therapy within 30 minutes of hospital presentation is the goal (if PCI is not possible) and reduces mortality if given within 12 hours of onset of symptoms

General Considerations

  • Results, in most cases, from an occlusive coronary thrombus at the site of a preexisting (though not necessarily severe) atherosclerotic plaque

  • More rarely, may result from prolonged vasospasm, inadequate myocardial blood flow (eg, hypotension), or excessive metabolic demand

  • Very rarely, may be caused by embolic occlusion, vasculitis, aortic root or coronary artery dissection, or aortitis

  • Cocaine use may cause infarction and should be considered in young individuals without risk factors

Clinical Findings

Symptoms and Signs

  • Recent onset of angina or alteration in the pattern of angina or chest pressure, squeezing or "indigestion"

  • Pain characteristics

    • Similar to angina in location and radiation but more severe

    • Usually occurs at rest, often in the early morning

    • Builds rapidly

    • Minimally responsive to sublingual nitroglycerin or oral opioids

  • Associated symptoms

    • Diaphoresis

    • Weakness

    • Apprehensiveness

    • Aversion to lying quietly

    • Light-headedness

    • Syncope

    • Dyspnea

    • Orthopnea

    • Cough

    • Wheezing

    • Nausea and vomiting

    • Abdominal bloating

  • 33% of patients do not experience chest pain, especially older patients, women, and patients with diabetes

  • Of all deaths due to myocardial infarction, ~50% occur before patient reaches the hospital, usually of ventricular fibrillation

  • Marked bradycardia (inferior infarction) to tachycardia (increased sympathetic activity, low cardiac output, or arrhythmia)

  • Jugular venous distention indicates right atrial hypertension, often from RV infarction or elevated LV filling pressures

  • Soft heart sounds may indicate LV dysfunction

  • S4 is common; S3 indicates significant LV dysfunction

  • Mitral regurgitation murmur usually indicates papillary muscle dysfunction or, rarely, rupture

  • Pericardial friction rubs are uncommon in the first 24 hours but may appear later

  • Edema is usually not present

  • Cyanosis and cold temperature indicate low output

  • Peripheral pulses should be noted, since later shock or emboli may alter the examination

Differential Diagnosis

  • Acute coronary syndrome without ST-segment elevation

  • Aortic dissection

  • Pulmonary embolism

  • Tension pneumothorax

  • Pericarditis

  • Esophageal rupture

  • Stress cardiomyopathy (Tako-Tsubo cardiomyopathy or apical ballooning syndrome)

Diagnosis

Laboratory Tests

  • Quantitative CK-MB, troponin I, and troponin T elevations as early as 4–6 h after onset; almost always abnormal by 8–12 h

  • Troponins

    • May remain elevated for ≤ 5–7 days

    • Therefore, not generally useful for evaluating suspected early reinfarction

  • High-sensitivity troponin assays

    • When positive, help enable myocardial infarction to ...

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