Heart Attack (Myocardial Infarction)
A heart attack, or myocardial infarction, is a medical emergency in which the supply of blood to the heart is suddenly and severely reduced or cut off, causing the muscle to die from lack of oxygen. More than 1.1 million people experience a heart attack (myocardial infarction) each year, and for many of them, the heart attack is their first symptom of coronary artery disease. A heart attack may be severe enough to cause death or it may be silent. As many as one out of every five people have only mild symptoms or none at all, and the heart attack may only be discovered by routine electrocardiography done some time later.
Not everyone has the same heart attack symptoms when having a myocardial infarction.
- About 2 out of every 3 people who have heart attacks have chest pain, shortness of breath or feel tired a few days or weeks before the attack.
- A person who has angina (temporary chest pain) may find that it happens more often after less and less physical activity. A change in the pattern of angina should be taken seriously.
- During a heart attack, a person may feel pain in the middle of the chest that can spread to the back, jaw or arms. The pain may also be felt in all of these places and not the chest. Sometime the pain is felt in the stomach area, where it may be taken for indigestion. The pain is like that of angina but usually more severe, longer lasting and does not get better by resting or taking a nitroglycerin pill.
- About 1 out of every 3 people who have heart attacks do not feel any chest pain. These people are more likely to be women, non-Caucasian, older than 75, someone with heart failure or diabetes and someone who has had a stroke.
Other common symptoms include:
- Sudden sweating
- Shortness of breath, especially in older people
- Heavy pounding of the heart
- Abnormal heart rhythms (arrhythmias), which occur in more than 90% of the people who have had a heart attack
- Loss of consciousness, which sometimes is the first symptom of a heart attack
- Feelings of restlessness, sweatiness, anxiety and a sense of impending doom
- Bluishness of the lips, hands or feet
- Older people may have symptoms that resemble a stroke and may become disoriented
Older people, especially women, often take longer than younger people to admit they are ill or to seek medical help
During the early hours of a heart attack, heart murmurs and other abnormal heart sounds may be heard through a stethoscope.
Causes and Risk Factors
A heart attack (myocardial infarction) is usually caused by a blood clot that blocks an artery of the heart. The artery has often already been narrowed by fatty deposits on its walls. These deposits can tear or break open, reducing the flow of blood and releasing substances that make the platelets of the blood sticky and more likely to form clots. Sometimes a clot forms inside the heart itself, then breaks away and gets stuck in an artery that feeds the heart. A spasm in one of these arteries can cause the blood flow to stop.
Because a heart attack (myocardial infarction) can be life threatening, men older than 35 or women older than 50 who have chest pain should be examined to see if they area having a heart attack. However, similar pain can be caused by pneumonia, a blood clot in the lung (pulmonary embolism), pericarditis, a rib fracture, spasm of the esophagus, indigestion or chest muscle tenderness after injury or exertion. A heart attack can be confirmed within a few hours of its occurrence by:
- Electrocardiography (ECG)
- Blood tests to measure levels of serum markers. The presence of these markers shows that there has been damage to or death of the heart muscle. These markers are normally found in the heart muscle, but they are released into the blood when the heart muscle is damaged.
- Echocardiography can be performed if the above tests do not give enough information
- Radionuclide imaging can also be done
Half the deaths from a heart attack occur in the first 3 or 4 hours after symptoms begin. It is crucial that symptoms of a heart attack be treated as a medical emergency. A person with these symptoms should be taken to the emergency department of a hospital in an ambulance with trained personnel.
The sooner that treatment of a heart attack begins, the better. Chewing an aspirin tablet after an ambulance has been called can help reduce the size of the blood clot. A beta-blocker may be given to slow the heart rate so the heart is not working as hard and to reduce the damage to the heart muscle. Often a person who is having a heart attack is given oxygen, which also helps heart tissue damage to be less.
People who may be having a heart attack are usually admitted to a hospital that has a cardiac care unit. Heart rhythm, blood pressure and the amount of oxygen in the blood are closely monitored so that heart damage can be assessed. Nurses in these units are specially trained to care for people with heart problems and to handle cardiac emergencies.
Drugs may be used to dissolve blood clots in the artery so that heart tissue can be saved. To be effective, these drugs must be given intravenously within six hours of the start of the symptoms of a heart attack. After six hours, most damage is permanent. (People who have bleeding conditions or severe high blood pressure and those who have had recent surgery or a stroke cannot be given these drugs.)
Instead of drug therapy, angioplasty may be performed immediately to clear the arteries. This approach is preferred as primary therapy in heart attacks. If the blockages are extensive, then coronary artery bypass surgery may be necessary.
Chances of surviving a heart attack can improve when an individual recognizes the symptoms early and seeks immediate medical attention. One out of every 10 people who have heart attacks, however, die within a year - usually within the first three or four months. Typically, these people continue to have chest pain, abnormal heart rhythms or heart failure. Older people and smaller people tend to not do as well after a heart attack as younger people and larger people. This may be one reason why women tend to fare less well than men after a heart attack - they tend to be both older and smaller, as well as have other disorders. They also tend to wait longer after a heart attack before going to the hospital.
After a heart attack (myocardial infarction), a doctor may require additional tests or treatment, including: