Myocardial Ischemia and Infarction

First Things First (assess for & treat the following)

• Is pt hemodynamically stable?
• Is pt continuing to have ischemia symptoms?
• Are high-risk features present (see below)?
• Does ECG show ST segment elevation or LBBB?
• Are there contraindications to thrombolytic therapy (if indicated)?
• Clinical syndromes
  
  • Chronic stable angina: fixed & stable coronary stenosis w/ absence of ischemia at rest, w/ ischemia provoked by normal physical states that increase myocardial metabolic demand (eg, physical exertion, emotional stress, post-prandial)
  • Unstable angina: broad category of self-limited ischemia in the absence of myocardial damage, as defined by an absence of serum cardiac enzyme elevation
    
    • Coronary plaque rupture w/ accumulation of intracoronary platelets & formation of transiently obstructing thrombus
      • Angina at rest, may be nocturnal
      • May follow recent history of MI
      • Represents the highest-risk group of pts w/ unstable angina
    • Previously stable coronary stenosis that slowly worsens due to progressive narrowing
      • Restenosis in the months following angioplasty is most common cause.
      • Gradually worsening exertional angina
    • Fixed & stable coronary stenosis w/ ischemia provoked by abnormal physical states that increase myocardial metabolic demand (eg, anemia, fever, tachyarrhythmia, hypotension, hyperthyroidism, cocaine use)
      • Symptoms abate as underlying disease process is corrected.
    • Coronary vasospasm
  • MI: resulting in death of muscle tissue & abnormal elevation of serum cardiac enzymes
    • Non-ST-segment-elevation MI (NSTEMI)
      • Infarction w/out elevation of ST segment on ECG
      • May result from occlusive thrombus, coronary vasospasm or fixed stenosis in the face of overwhelming myocardial oxygen demand or low oxygen delivery (supply-demand mismatch)
    • ST-segment-elevation MI (STEMI)
      • Infarction w/ elevation of ST segment in the ECG leads localized to the region of infarcting myocardium
      • Persistent coronary occlusion results in significant myocardial necrosis.
  • Acute coronary syndrome: defined as spectrum of the above clinical syndromes that arise from coronary plaque rupture & intracoronary thrombus formation (unstable angina, NSTEMI, STEMI)