Myocardial Infarction, Acute with ST-Segment Elevation

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 (MI), ~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 ...