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Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms,〔 with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.〔 Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol intake, among others. The mechanism of an MI often involves the rupture of an atherosclerotic plaque, leading to complete blockage of a coronary artery.〔 MIs are less commonly caused by coronary artery spasms, which may be due to cocaine, significant emotional stress, and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests, and coronary angiography. An ECG may confirm an ST elevation MI if ST elevation is present.〔 Commonly used blood tests include troponin and less often creatine kinase MB.〔 Aspirin is an appropriate immediate treatment for a suspected MI.〔 Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes.〔〔 Supplemental oxygen should be used in those with low oxygen levels or shortness of breath. In ST elevation MIs treatments which attempt to restore blood flow to the heart are typically recommended and include angioplasty, where the arteries are pushed open, or thrombolysis, where the blockage is removed using medications.〔 People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use angioplasty in those at high risk.〔 In people with blockages of multiple coronary arteries and diabetes, bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers, and statins, are typically recommended.〔 Worldwide, more than 3 million people have ST elevation MIs and 4 million have NSTEMIs each year. STEMIs occur about twice as often in men as women. About one million people have an MI each year in the United States.〔 In the developed world the risk of death in those who have had an STEMI is about 10%. Rates of MI for a given age have decreased globally between 1990 and 2010. ==Signs and symptoms== The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous.〔National Heart, Lung and Blood Institute. (Heart Attack Warning Signs ). Retrieved November 22, 2006.〕 Chest pain is the most common symptom of acute MI 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 upper abdomen, where it may mimic heartburn. Levine's sign, in which a person localizes the chest pain by clenching their fists over their sternum, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed it had a poor positive predictive value. 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. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system, which occurs in response to pain and the blood flow abnormalities that result from dysfunction of the heart muscle. Loss of consciousness (due to inadequate blood flow to the brain and cardiogenic shock) and sudden death (frequently due to the development of ventricular fibrillation) can occur in MIs.〔 Atypical symptoms are more frequently reported by women, the elderly, and those with diabetes when compared to their male and younger counterparts. Women also report more numerous symptoms compared with men (2.6 on average vs. 1.8 symptoms in men).〔 The most common symptoms of MI in women include dyspnea, weakness, and fatigue. Fatigue, sleep disturbances, and dyspnea have been reported as frequently occurring symptoms that may manifest as long as one month before the actual clinically manifested ischemic event. In women, chest pain may be less predictive of coronary ischemia than in men. Women may also experience back or jaw pain during an episode.〔http://feministing.com/2012/02/23/for-women-heart-attacks-look-different-and-so-do-heart-health-outcomes/〕 At least one quarter of all MIs are silent, without chest pain or other symptoms.〔 These cases can be discovered later on electrocardiograms, using blood enzyme tests, or at autopsy without a prior history of related complaints. Estimates of the prevalence of silent MIs vary between 22 and 64%.〔 A silent course is more common in the elderly,〔 in people with diabetes mellitus and after heart transplantation, probably because the donor heart is not fully innervated by the nervous system of the recipient. In people with diabetes, differences in pain threshold, autonomic neuropathy, and psychological factors have been cited as possible explanations for the lack of symptoms.〔 Any group of symptoms compatible with a sudden interruption of the blood flow to the heart, which includes STEMI, NSTEMI or unstable angina, are called an acute coronary syndrome.〔(Acute Coronary Syndrome ). American Heart Association. Retrieved November 25, 2006.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「myocardial infarction」の詳細全文を読む スポンサード リンク
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