Text 1:

Myocardial infarction (MI), colloquially known as “heart attack,” is caused by decreased or complete cessation of blood flow to a portion of the myocardium. Myocardial infarction may be “silent” and go undetected, or it could be a catastrophic event leading to hemodynamic deterioration and sudden death.

Most myocardial infarctions are due to underlying coronary artery disease, the leading cause of death in the United States. With coronary artery occlusion, the myocardium is deprived of oxygen. Prolonged deprivation of oxygen supply to the myocardium can lead to myocardial cell death and necrosis.

Patients can present with chest discomfort or pressure that can radiate to the neck, jaw, shoulder, or arm. In addition to the history and physical exam, myocardial ischemia may be associated with ECG changes and elevated biochemical markers such as cardiac troponins.

Text 2: Etiology

As stated above, myocardial infarction is closely associated with coronary artery disease. INTERHEART is an international multi-center case-control study which delineated the following modifiable risk factors for coronary artery disease:

1.    Smoking

2.    Abnormal lipid profile/blood apolipoprotein

3.    Hypertension

4.    Diabetes mellitus

5.    Abdominal obesity (waist/hip ratio) (greater than 0.90 for males and greater than 0.85 for females)

6.    Psychosocial factors such as depression, loss of the locus of control, global stress, financial stress, and life events including marital separation, job loss, and family conflicts

7.    Lack of daily consumption of fruits or vegetables

8.    Lack of physical activity

9.    Alcohol consumption (weaker association, protective)

The INTERHEART study showed that all the above risk factors were significantly associated with acute myocardial infarction except for alcohol consumption, which showed a weaker association. Smoking and abnormal apolipoprotein ratio showed the strongest association with acute myocardial infarction. The increased risk associated with diabetes and hypertension were found to be higher in women, and the protective effect of exercise and alcohol was also found to be higher in women.

Other risk factors include a moderately high level of plasma homocysteine, which is an independent risk factor of MI. Elevated plasma homocysteine is potentially modifiable and can be treated with folic acid, vitamin B6, and vitamin B12.

Some non-modifiable risk factors for myocardial infarction include advanced age, male gender (males tend to have myocardial infarction earlier in life),

genetics (there is an increased risk of MI if a first-degree relative has a

history of cardiovascular events before the age of 50). The role of genetic loci that increase the risk for MI is under active investigation.

Text 3

Pathophysiology

The acute occlusion of one or multiple large epicardial coronary arteries for more than 20 to 40 minutes can lead to acute myocardial infarction. The occlusion is usually thrombotic and due to the rupture of a plaque formed in the coronary arteries. The occlusion leads to a lack of oxygen in the myocardium, which results in sarcolemmal disruption and myofibril relaxation. These changes are one of the first ultrastructural changes in the process of MI, which are followed by mitochondrial alterations. The prolonged ischemia ultimately results in liquefactive necrosis of myocardial tissue. The necrosis spreads from sub-endocardium to sub-epicardium. The subepicardium is believed to have increased collateral circulation, which delays its death.[2] Depending on the territory affected by the infarction, the cardiac function is compromised. Due to the negligible regeneration capacity of the myocardium, the infarcted area heals by scar formation, and often, the heart is remodeled characterized by dilation, segmental hypertrophy of remaining viable tissue, and cardiac dysfunction.

History and Physical

The imbalance between oxygen supply and the demand leads to myocardial ischemia and can sometimes lead to myocardial infarction. The patient’s history, electrocardiographic findings, and elevated serum biomarkers help identify ischemic symptoms. Myocardial ischemia can present as chest pain, upper extremity pain, mandibular, or epigastric discomfort that occurs during exertion or at rest. Myocardial ischemia can also present as dyspnea or fatigue, which are known to be ischemic equivalents. The chest pain is usually retrosternal and is sometimes described as the sensation of pressure or heaviness. The pain often radiates to the left shoulder, neck, or arms with no obvious precipitating factors, and it may be intermittent or persistent. The pain usually lasts for more than 20 minutes. It is usually not affected by positional changes or active movement of the region. Additional symptoms, such as sweating, nausea, abdominal pain, dyspnea, and syncope, may also be present. The MI can also present atypically with subtle findings such as palpitations, or more dramatic manifestations, such as cardiac arrest. The MI can sometimes present with no symptoms.

Text 4:

Medications play a crucial role in heart attack treatment. Anti-clotting medications, such as aspirin and other blood-thinning medicines, are used to prevent further blood clot formation. Nitroglycerin is administered to alleviate chest pain and widen blood vessels, promoting easier blood flow. 

Thrombolytic medications, known as clot-busting drugs, are utilized within the first 12 hours after a heart attack to dissolve blood clots.

Anti-arrhythmia medications are prescribed to address irregular heart rhythms that can occur during a heart attack. Pain medications, including morphine, are often provided to relieve chest pain.

Percutaneous coronary intervention (PCI) is a procedure used to restore circulation to the affected heart muscle. It involves the insertion of a catheter-based device into a major blood vessel, typically in the upper thigh or wrist. This procedure is essential for restoring blood flow, and the time taken for PCI after the patient's arrival at the Emergency Room is measured as "door-to-balloon time." Placement of a stent at the site of the blockage is a common aspect of PCI to maintain open arteries and prevent future blockages.