Myocardial infarction

• 1. Defining The Heart Attack

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  A myocardial infarction occurs when blood flow decreases or stops in one of the arteries of the heart. This interruption causes tissue death to the heart muscle itself. Medical professionals call this process infarction. It is a type of acute coronary syndrome that describes sudden changes in symptoms related to blood flow. Unlike unstable angina, which involves pain without cell death, an MI always includes actual damage to cells. Doctors measure this damage by checking for specific proteins in the blood called biomarkers. The most common symptom is retrosternal chest pain or discomfort. This pain classically radiates to the left shoulder, arm, or jaw. Sometimes the sensation feels like heartburn instead of pressure.

• 2. Symptoms And Atypical Presentations

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  About 30% of people experience atypical symptoms during a heart attack. Women more often present without chest pain and instead have neck pain or feel tired. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. These silent cases can be discovered later on electrocardiograms or at autopsy after a person has died. Such silent myocardial infarctions represent between 22 and 64% of all infarctions. They are more common in the elderly and in those with diabetes mellitus. Females are less likely to report chest pain and more likely to report nausea, jaw pain, neck pain, cough, and fatigue. Shortness of breath is a common, and sometimes the only symptom, occurring when damage to the heart limits the output of the left ventricle.

• 3. Risk Factors And Biological Mechanisms

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  The complete blockage of a coronary artery caused by a rupture of an atherosclerotic plaque is usually the underlying mechanism of an MI. Atherosclerosis involves the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of the coronary arteries. Inflammatory cells move into affected arterial walls and become laden with cholesterol products. Over time they form foam cells that create a cholesterol core. If there is ongoing inflammation, the cap may be thin or ulcerate. Exposed to pressure from blood flow, these plaques may rupture and trigger the formation of a blood clot. Smoking appears to be the cause of about 36% of coronary artery disease. Obesity accounts for 20% of cases. Lack of physical activity has been linked to 7, 12% of cases. High levels of blood cholesterol is a known risk factor, particularly high low-density lipoprotein.

• 4. Diagnostic Tools And Classification Systems

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  An electrocardiogram records the heart's electrical activity to confirm an ST elevation MI if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB. Troponins are considered the best biomarkers because they have greater sensitivity and specificity for measuring injury to the heart muscle. A rise in troponin occurs within 2, 3 hours of injury to the heart muscle. STEMIs make up about 25, 40% of myocardial infarctions. These classifications are based on ST elevation, a portion of a heartbeat graphically recorded on an ECG. Non-ST elevation MIs are managed differently than those with ST elevation. Imaging tests like echocardiography can visualize the heart and its abnormal motion as it beats. Chest X-rays help explore alternate causes of chest pain.

• 5. Emergency Treatments And Surgical Interventions

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  Treatment of an MI is time-critical and requires immediate medical attention. Aspirin is an appropriate immediate treatment for a suspected MI. In a STEMI, treatments attempt to restore blood flow to the heart using percutaneous coronary intervention or thrombolysis. Percutaneous coronary intervention involves pushing arteries open and may be stented. Thrombolysis removes the blockage using medications like tissue plasminogen activator. Primary percutaneous coronary intervention is the treatment of choice if it can be performed within 90, 120 minutes of contact with a medical provider. People who have non-ST elevation myocardial infarction are often managed with the blood thinner heparin. Coronary artery bypass surgery may be recommended in people with blockages of multiple coronary arteries and diabetes. Oxygen is currently only recommended if oxygen levels are found to be low.

• 6. Long-Term Management And Rehabilitation

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  After an MI, lifestyle modifications along with long-term treatment with aspirin, beta blockers and statins are typically recommended. Cardiac rehabilitation benefits many who have experienced myocardial infarction even if there has been substantial heart damage. The program includes lifestyle advice, exercise, social support, and recommendations about driving and flying. Returning to sexual activity after myocardial infarction is a major concern for most patients. Exercise-based cardiovascular rehabilitation programs reduce the risk of a myocardial infarction and improve health-related quality of life. Statins decrease the incidence and mortality rates of myocardial infarctions. Beta blocker therapy should be started within 24 hours provided there is no acute heart failure or heart block. ACE inhibitor therapy should be started within 24 hours and continued indefinitely at the highest tolerated dose.

• 7. Global Epidemiology And Health Disparities

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  Worldwide, about 15.9 million myocardial infarctions occurred in 2015. More than 3 million people had an ST elevation MI and more than 4 million had an NSTEMI. 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 a STEMI is about 10%. Rates of MI for a given age have decreased globally between 1990 and 2010. Social determinants such as neighborhood disadvantage and lack of social support play an important role in survival. Among individuals who live in low-socioeconomic areas, which is close to 25% of the US population, myocardial infarctions occurred twice as often compared with people who lived in higher SES areas. African Americans have a greater burden of myocardial infarction and other cardiovascular events.