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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Prolonged chest discomfort

  • Characteristic ECG changes:

    • – New ST elevation at the J point in at least 2 contiguous leads ≥ 2 mm in men or ≥ 1.5 mm in women in leads v2–v3; ≥ 1 mm in other contiguous chest leads or the limb leads in absence of left ventricular hypertrophy or LBBB

    • – Elevated marker protein such as troponin

  • Cardiac imaging showing reduced regional perfusion or segmental wall motion abnormalities with normal wall thickness

    • – In the elderly, women, and diabetics, the presentation can be atypical

    • – Cardiac biomarkers (troponin elevation)

GENERAL CONSIDERATIONS

  • Injury to myocardial tissue caused by an imbalance between myocardial oxygen supply and demand, usually due to acute coronary artery occlusion by thrombosis in situ

  • Coronary artery atherosclerosis is an essential component of the process in most patients

  • Rupture of an atherosclerotic plaque with subsequent acute thrombus formation is the usual mechanism

  • Inflammation plays a pivotal role in the genesis of plaque rupture

  • About 50% of deaths occur within 1 hour, most frequently due to ventricular fibrillation

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Chest discomfort is usually in the center of the anterior chest radiating to the left arm or neck

  • Individual patients may vary widely in the character, location, and radiation of chest discomfort

  • The patient may place a hand over the sternum (Levine’s sign)

  • Women have more atypical symptoms

  • Diabetics and the elderly may not complain of chest discomfort (silent infarct) but may have other features of an infarction such as heart failure

  • Dyspnea, diaphoresis, nausea, or vomiting may occur

PHYSICAL EXAM FINDINGS

  • S4 is heard frequently

  • Signs of heart failure such as S3, neck vein distention, and rales occur with larger infarcts

  • Cold perspiration and skin pallor may be seen in those with left ventricular failure and sympathetic stimulation

  • Sinus tachycardia and frequent premature ventricular beats are common (bradycardia not uncommon in inferior myocardial infarction [MI])

  • Systolic blood pressure may be < 90 mm Hg in those with cardiogenic shock

  • Murmurs or rubs may occur as complications of MI

    • – Systolic murmur with mitral regurgitation

    • – Pericardial rub in pericarditis

DIFFERENTIAL DIAGNOSIS

  • Stable angina pectoris

  • Variant angina

  • Unstable angina

  • Aortic dissection

  • Acute myopericarditis

  • Stress cardiomyopathy (takotsubo syndrome)

  • Acute pulmonary embolism

  • Esophageal reflux

  • Cholecystitis

  • Peptic ulcer disease

  • Cervical radiculopathy

  • Costochondritis

  • Pneumothorax

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • CBC, brain natriuretic peptide testing

  • Cardiac biomarkers (troponin T or I)

  • Other tests depend on differential diagnosis, which may include amylase, lipase, liver function tests, or D-dimer levels

  • Arterial blood gas analysis if hypoxemia is found on pulse oximetry

  • Urine analysis including drug screen for cocaine in young patients with MI or patients with history of drug use

ELECTROCARDIOGRAPHY

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