Myocardial infarction (MI) is the death of cardiac muscle tissue (myocardium) due to the occlusion (clogging) of a branch of the coronary artery, usually the anterior descending branch of the left coronary artery. This causes an irreversible necrosis of the heart muscle because of the interruption of blood supply to the heart. Also known as heart attack, myocardial infarction occurs when a coronary artery (a blood vessel that supplies the heart) are blocked by cholesterol plaque or blood clots, preventing enough oxygen from getting to the heart muscle cells (fibers). Thus, the myocardium dies or becomes permanently damaged. The occlusion of one of these blood vessels causes ischemia, which is an insufficient supply of blood to a body tissue.
The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous. Chest pain is the most common symptom of acute myocardial infarction and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia (a lack of blood and hence oxygen supply) of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and epigastrium, where it may mimic heartburn. Shortness of breath (dyspnea) occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis (an excessive form of sweating), weakness, light-headedness, nausea, vomiting, and palpitations.
The diagnostic tests available to detect heart muscle damage are an electrocardiogram (ECG), echocardiography, and various blood tests. The most often used markers are the creatine kinase-MB (CK-MB) fraction and the troponin levels. Immediate treatment for suspected acute myocardial infarction includes oxygen, aspirin, and sublingual nitroglycerin.
What causes a Myocardial infarction (Video Animation)