health

Myocardial infarction

Myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to a part of the heart, causing damage to the heart muscle.^[1] The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw.^[1] Often it occurs in the center or left side of the chest and lasts for more than a few minutes.^[1]The discomfort may occasionally feel like heartburn.^[1] Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired.^[1] About 30% of people have atypical symptoms.^[7] Women more often have atypical symptoms than men.^[10] Among those over 75 years old, about 5% have had an MI with little or no history of symptoms.^[11] An MI may cause heart failure, an irregular heartbeat, cardiogenic shock, or cardiac arrest.

Signs and symptoms

Pain

Chest pain is the most common symptom of acute myocardial infarction and is often described as a sensation of tightness, pressure, or squeezing. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen.^[24] The pain most suggestive of an acute MI, with the highest likelihood ratio, is pain radiating to the right arm and shoulder.^[25] Similarly, chest pain similar to a previous heart attack is also suggestive.^[26] The pain associated with MI is usually diffuse, does not change with position, and lasts for more than 20 minutes.

Tissue death

Drawing of the heart showing anterior left ventricle wall infarction
If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the blocked coronary artery die (infarction), chiefly through necrosis, and do not grow back. A collagen scar forms in their place.^[59] When an artery is blocked, cells lack oxygen, needed to produce ATP in mitochondria. ATP is required for the maintenance of electrolyte balance, particularly through the Na/K ATPase. This leads to an ischemic cascade of intracellular changes, necrosis and apoptosis of affected cells.^[62]Cells in the area with the worst blood supply, just below the inner surface of the heart (endocardium), are most susceptible to damage.^[63]Ischemia first affects this region, the subendocardial region, and tissue begins to die within 15–30 minutes of loss of blood supply.^[64] The dead tissue is surrounded by a zone of potentially reversible ischemia that progresses to become a full-thickness transmural infarct.^[62][64]The initial "wave" of infarction can take place over 3–4 hours
Electrocardiogram[edit]A 12-lead ECG showing a STEMI. Elevation of the ST segment can be seen in some leads.
Electrocardiograms (ECGs) are a series of leads placed on a person's chest that measure electrical activity associated with contraction of heart muscle.^[70] The taking of an ECG is an important part in the workup of an AMI,^[22] and ECGs are often not just taken once, but may be repeated over minutes to hours, or in response to changes in signs or symptoms