Acute myocardial infarction, or heart attack, refers to necrosis (death) of myocardial tissue that results from ischemia (deprivation of oxygen) associated with sudden, prolonged diminished blood flow. Every year, nearly 1.5 million individuals in the US suffer an AMI (approximately one heart attack every 20 seconds), and of these approximately 500,000 die. Ischemic heart disease is the principal cause of death in the US. The associated health care costs are enormous.

The most common cause of AMI is an obstruction in the coronary arteries (atherosclerotic coronary artery disease). The disease process begins with a fatty streak on blood vessel surfaces that may enlarge with time to become a fatty plaque and then a thrombus (clot). This process causes reduction in blood flow to the heart and therefore reduction in the amount of oxygen supplied to the surrounding heart tissue (myocardial ischemia). When the obstruction becomes large enough to totally obstruct the blood flow AMI occurs. Complete obstruction of blood flow results in necrosis of heart tissue in the affected region within 20 minutes. Maximal irreversible injury occurs within 6 hours.

Salvage of the myocardium depends on restoring blood flow to the affected area as quickly as possible.

Diagnosis of Acute Myocardial Infarction (AMI)

As established by the World Health Organization, the diagnosis of AMI requires at least two of the following criteria:

• A history of angina (chest pain)
  
  
• Characteristic changes in the ECG (EKG)
  
  
• Elevated levels of cardiac markers