Myocardial infarction

Myocardial infarction

  • Healing process
    • Within 24 hours, leukocytes infiltrate the area of cell death
    • Proteolytic enzymes of neutrophils and macrophages begin to remove necrotic tissue by fourth day → thin wall
    • Necrotic zone identifiable by ECG changes
    • Collagen matrix laid down
    • 10 to 14 days after MI, scar tissue is still weak
    • Heart muscle vulnerable to stress
    • Monitor patient carefully as activity level increases
    • By 6 weeks after MI, scar tissue has replaced necrotic tissue
      • Area is said to be healed, but less compliant
    • Ventricular remodeling
      • Normal myocardium will hypertrophy and dilate in an attempt to compensate for infarcted muscle
  • Complications of myocardial infarction
    • Dysrhythmias
      • Most common complication
      • Present in 80% to 90% of MI patients
      • Can be caused by ischemia, electrolyte imbalances, or SNS stimulation
      • VT and VF are most common cause of death in prehospitalization period
    • Heart failure
      • Occurs when pumping power of heart has diminished
      • Left-sided HF
        • Mild dyspnea, restlessness, agitation, slight tachycardia initially
      • Right-sided HF
        • Jugular venous distention, hepatic congestion, lower extremity edema
    • Cardiogenic shock
      • Occurs because of
        • Severe LV failure, papillary muscle rupture, ventricular septal rupture, LV free wall rupture, right ventricular infarction
      • Requires aggressive management
        • Associated with a high death rate
    • Papillary muscle dysfunction or rupture
      • Causes mitral valve regurgitation
      • Aggravates an already compromised LV → rapid clinical deterioration
    • Left ventricular aneurysm
      • Myocardial wall becomes thinned and bulges out during contraction
      • Leads to HF, dysrhythmias, and angina
    • Ventricular septal wall rupture and left ventricular free wall rupture
      • New, loud systolic murmur
      • HF and cardiogenic shock
      • Emergency repair
      • Rare condition associated with high death rate
    • Acute pericarditis
      • Inflammation of visceral and/or parietal pericardium
      • Mild to severe chest pain
        • Increases with inspiration, coughing, movement of upper body
        • Relieved by sitting in forward position
      • Pericardial friction rub
      • ECG changes
    • Dressler syndrome
      • Pericarditis and fever that develops 1 to 8 weeks after MI
      • Chest pain, fever, malaise, pericardial friction rub, arthralgia
      • High dose aspirin is treatment of choice