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Acute ST Elevation Myocardial Infarction

Definition

  • Acute ST-elevation myocardial infarction (STEMI)
    • Characterized by clinical findings of acute infarction and ST-segment elevation on 12-lead electrocardiogram (ECG)
    • Generally occurs when coronary blood flow decreases abruptly after a thrombotic occlusion of a coronary artery
    • Early identification and reperfusion are critical for reducing morbidity and mortality.
  • See Unstable Angina and Non ST Elevation Myocardial Infarction.

Epidemiology

  • Incidence
    • One of the most common diagnoses in hospitalized patients in industrialized countries
    • In the U.S.
      • ~650,000 patients have a new acute MI each year.
        • ~370,000 are STEMI, and the remainder are non–ST-elevation myocardial infarction (NSTEMI).
      • 450,000 patients have a recurrent acute MI each year.
  • Age
    • Incidence increases with advancing age.
  • Sex
    • More common in men

Risk Factors

  • Common
    • Age
      • Men ≥ 50 years
      • Women ≥ 60 years
      • Incidence increases with age in both sexes.
    • Cigarette smoking
    • Hypertension
      • Blood pressure ≥ 140/90 mmHg or using antihypertensive medication
    • Low high-density lipoprotein cholesterol level
      • < 40 mg/dL
    • High low-density lipoprotein cholesterol level
      • >130 mg/dL
    • Diabetes mellitus
    • Metabolic syndrome
    • Family history of premature coronary heart disease (CHD)
      • CHD in male first-degree relative < 55 years
      • CHD in female first-degree relative < 65 years
    • Lifestyle risk factors
      • Obesity (body mass index ≥ 30 kg/m2)
      • Physical inactivity
    • Unstable angina
    • Prinzmetal’s variant angina
  • Less common
    • Hypercoagulability
    • Collagen vascular disease
    • Cocaine abuse
    • Intracardiac thrombi or masses that can produce coronary emboli
  • Emerging risk factors
    • Low levels of vitamin D [1]
    • Lipoprotein(a)
    • Elevated lipoprotein-associated phospholipase A2
    • Prothrombotic factors
    • Proinflammatory factors, as reflected in elevated C-reactive protein level
    • Impaired glucose tolerance
    • Ischemic stroke
      • Absolute risk of MI or vascular death after ischemic stroke, even in those without high-risk features, approximates levels used by national organizations to designate groups of patients at high risk of vascular events.
  • Medications[2][3]
    • Cyclooxygenase (COX)-2 inhibitors
      • Several have been discontinued.
      • Celecoxib is still in use and under study; drug carries warning that it may increase risk of cardiovascular events.
    • Nonselective NSAIDs (controversial)

Etiology

  • STEMI usually occurs when coronary blood flow ceases or decreases abruptly, after thrombotic occlusion of a coronary artery previously affected by atherosclerosis.
    • In most cases, infarction occurs when an atherosclerotic plaque ruptures or fissures, and when conditions (local or systemic) favor thrombogenesis.
      • Mural thrombus forms at the site of rupture and leads to coronary occlusion.
    • Histologic studies indicate that the coronary plaques prone to rupture are those with a rich lipid core and a thin fibrous cap.
  • In rare cases, STEMI may be due to coronary artery occlusion caused by:
    • Coronary emboli
    • Congenital abnormalities
    • Coronary spasm
    • Wide variety of systemic—particularly inflammatory—diseases
  • The amount of myocardial damage caused by coronary occlusion depends on:
    • The territory supplied by the affected vessel
    • Whether or not the vessel becomes totally occluded
    • The duration of coronary occlusion
    • The quantity of blood supplied by collateral vessels to the affected tissue
    • The demand for oxygen of the myocardium, whose blood supply has been suddenly limited
    • Native factors that can produce early spontaneous lysis of the occlusive thrombus
    • The adequacy of myocardial perfusion in the infarct zone when flow is restored in the occluded epicardial coronary artery
  • In up to half of cases, precipitating factors such as the following are implicated in STEMI:
    • Vigorous physical exercise
    • Emotional stress
    • Medical or surgical illness
    • Cocaine abuse (rare)

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Last updated: July 16, 2009
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