A heart attack is when blood vessels that supply blood to the heart are blocked, preventing enough oxygen from getting to the heart. The heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction.

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart starves for oxygen and heart cells die.

In atherosclerosis, plaque builds up in the walls of your coronary arteries. This plaque is made up of cholesterol and other cells. A heart attack can occur as a result of the following:

• The slow buildup of plaque may almost block one of your coronary arteries. A heart attack may occur if not enough oxygen-containing blood can flow through this blockage. This is more likely to happen when you are exercising.
• The plaque itself develops cracks (fissures) or tears. Blood platelets stick to these tears and form a blood clot (thrombus). A heart attack can occur if this blood clot completely blocks the passage of oxygen-rich blood to the heart.

Occasionally, sudden overwhelming stress can trigger a heart attack.

Risk factors for heart attack and coronary artery disease include:

• Increasing age (over age 65)
• Male gender
• Diabetes
• Family history of coronary artery disease (genetic or hereditary factors)
• High blood pressure
• Smoking
• Too much fat in your diet
• Unhealthy cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol
• Chronic kidney disease

Chest pain is a major symptom of heart attack. You may feel the pain in only one part of your body, or it may move from your chest to your arms, shoulder, neck, teeth, jaw, belly area, or back.

The pain can be severe or mild. It can feel like:

• A tight band around the chest
• Bad indigestion
• Something heavy sitting on your chest
• Squeezing or heavy pressure

The pain usually lasts longer than 20 minutes. Rest and a medicine called nitroglycerin do not completely relieve the pain of a heart attack. Symptoms may also go away and come back.

Other symptoms of a heart attack include:

• Anxiety
• Cough
• Fainting
• Light-headedness, dizziness
• Nausea or vomiting
• Palpitations (feeling like your heart is beating too fast)
• Shortness of breath
• Sweating, which may be extreme

Some people (the elderly, people with diabetes, and women) may have little or no chest pain. Or, they may experience unusual symptoms (shortness of breath, fatigue, weakness). A "silent heart attack" is a heart attack with no symptoms.

A heart attack is a medical emergency. If you have symptoms of a heart attack, seek immediate medical help. Call 911 or your local emergency number immediately. DO NOT try to drive yourself to the hospital. DO NOT DELAY, because you are at greatest risk of sudden cardiac death in the early hours of a heart attack.

The health care provider will perform a physical exam and listen to your chest using a stethoscope. The doctor may hear abnormal sounds in your lungs (called crackles), a heart murmur, or other abnormal sounds.

You may have a rapid pulse. Your blood pressure may be normal, high, or low.

Tests to look at your heart include:

• Coronary angiography
• CT scan
• Echocardiography
• Electrocardiogram (ECG) -- once or repeated over several hours
• MRI
• Nuclear ventriculography

Blood tests can help show if you have substances produced by heart tissue damage or a high risk for heart attack. These tests include:

• Troponin I and troponin T
• CPK and CPK-MB
• Serum myoglobin

If you had a heart attack, you will need to stay in the hospital, possibly in the intensive care unit (ICU). You will be hooked up to an ECG machine, so the health care team can look at how your heart is beating.

Life-threatening irregular heartbeats (arrhythmias) are the leading cause of death in the first few hours of a heart attack. These arrythmias may be treated with medications or electrical cardioverson/defibrillation.

The health care team will give you oxygen, even if your blood oxygen levels are normal. This is done so that your body tissues have easy access to oxygen and your heart doesn't have to work as hard.

An intravenous line (IV) will be placed into one of your veins. Medicines and fluids pass through this IV. You may need a tube inserted into your bladder (urinary catheter) so that doctors can see how much fluid your body removes.

ANGIOPLASTY AND STENT PLACEMENT

Angioplasty, also called percutaneous coronary intervention (PCI), is the preferred emergency procedure for opening the arteries for some types of heart attacks. It should preferably be performed within 90 minutes of arriving at the hospital and no later than 12 hours after a heart attack.

Angioplasty is a procedure to open narrowed or blocked blood vessels that supply blood to the heart.

A coronary artery stent is a small, metal mesh tube that opens up (expands) inside a coronary artery. A stent is often placed after angioplasty. It helps prevent the artery from closing up again. A drug eluting stent has medicine in it that helps prevent the artery from closing.

THROMBOLYTIC THERAPY (CLOT-BUSTING DRUGS)

Depending on the results of the ECG, certain patients may be given drugs to break up the clot. It is best if these drugs are given within 3 hours of when the patient first felt the chest pain. This is called thrombolytic therapy. The medicine is first given through an IV. Blood thinners taken by mouth may be prescribed later to prevent clots from forming.

Thrombolytic therapy is not appropriate for people who have:

• Bleeding inside their head (intracranial hemorrhage)
• Brain abnormalities such as tumors or blood vessel malformations
• Stroke within the past 3 months (or possibly longer)
• Head injury within the past 3 months

Thrombolytic therapy is extremely dangerous in women who are pregnant or in people who have:

• A history of using blood thinners such as coumadin
• Had major surgery or a major injury within the past 3 weeks
• Had internal bleeding within the past 2-4 weeks
• Peptic ulcer disease
• Severe high blood pressure

OTHER MEDICINES FOR HEART ATTACKS

Many different medicines are used to treat and prevent heart attacks. Nitroglycerin helps reduce chest pain. You may also receive strong medicines to relieve pain.

Antiplatelet medicines help prevent clots from forming. Aspirin is an antiplatelet drug. Another one is clopidogrel (Plavix). Ask your doctor which of these drugs you should be taking. Always talk to your health care provider before stopping either of these drugs.

• For the first year after a heart attack, you will likely take both aspirin and clopidogrel every day. After that, your health care provider may only prescribe aspirin.
• If you had angioplasty and a coronary stent placed after your heart attack, you may need to take clopidogrel with your aspirin for longer than one year.

Other medications you may receive during or after a heart attack include:

• Beta-blockers (such as metoprolol, atenolol, and propranolol) help reduce the strain on the heart and lower blood pressure.
• ACE inhibitors (such as ramipril, lisinopril, enalapril, or captopril) are used to prevent heart failure and lower blood pressure.
• Lipid-lowering medications, especially statins (such as lovastatin, pravastatin, simvastatin, atorvastatin, and rosuvastatin) reduce blood cholesterol levels to prevent plaque from increasing. They may reduce the risk of another heart attack or death.

CORONARY ARTERY BYPASS SURGERY

Coronary angiography may reveal severe coronary artery disease in many vessels, or a narrowing of the left main coronary artery (the vessel supplying most of the blood to the heart). In these circumstances, the cardiologist may recommend emergency coronary artery bypass surgery (CABG). This procedure is also called "open heart surgery." The surgeon takes either a vein or artery from another location in your body and uses it to bypass the blocked coronary artery.

See:Heart disease -- resources

How well you do after a heart attack depends on the amount and location of damaged tissue. Your outcome is worse if the heart attack caused damage to the signaling system that tells the heart to contract.

About a third of heart attacks are deadly. If you live 2 hours after an attack, you are likely to survive, but you may have complications. Those who do not have complications may fully recover.

Usually a person who has had a heart attack can slowly go back to normal activities, including sexual activity.

• Cardiogenic shock
• Congestive heart failure
• Damage extending past heart tissue (infarct extension), possibly leading to rupture of the heart
• Damage to heart valves or the wall between the two sides of the heart
• Inflammation around the lining of the heart (pericarditis)
• Irregular heartbeats, including ventricular tachycardia and ventricular fibrillation
• Blood clot in the lungs (pulmonary embolism)
• Blood clot to the brain (stroke)
• Side effects of drug treatment

Immediately call your local emergency number (such as 911) if you have symptoms of a heart attack.

To prevent a heart attack:

• Keep your blood pressure, blood sugar, and cholesterol under control.
• Don't smoke.
• Consider drinking 1 to 2 glasses of alcohol or wine each day. Moderate amounts of alcohol may reduce your risk of cardiovascular problems. However, drinking larger amounts does more harm than good.
• Eat a low-fat diet rich in fruits and vegetables and low in animal fat.
• Eat fish twice a week. Baked or grilled fish is better than fried fish. Frying can destroy some of the health benefits.
• Exercise daily or several times a week. Walking is a good form of exercise. Talk to your doctor before starting an exercise routine.
• Lose weight if you are overweight.

If you have one or more risk factors for heart disease, talk to your doctor about possibly taking aspirin to help prevent a heart attack. Aspirin therapy (75 mg to 325 mg a day) or a drug called clopidogrel may be prescribed for women at high risk for heart disease.

Aspirin therapy is recommended for women over age 65 to prevent a heart attack and stroke. However, it is only recommended if blood pressure is controlled and the benefit is likely to outweigh the risk of gastrointestinal side effects. Regular use of aspirin is not recommended for healthy women under age 65 to prevent heart attacks.

New guidelines no longer recommend hormone replacement therapy, vitamins E or C, antioxidants, or folic acid to prevent heart disease.

After a heart attack, you will need regular follow-up care to reduce the risk of having a second heart attack. Often, a cardiac rehabilitation program is recommended to help you gradually return to a normal lifestyle. Always follow the exercise, diet, and medication plan prescribed by your doctor.

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Goodman SG, Menon V, Cannon CP, Steg G, Ohman EM, Harrington RA, et al. Acute ST-segment elevation myocardial infarction: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th edition). Chest. 2008;133:708S-775S.