A heart attack (myocardial infarction) occurs when an area of heart muscle dies or is permanently damaged because of an inadequate supply of oxygen to that area.

Alternative Names

Myocardial infarction; MI; Acute MI

Causes, incidence, and risk factors

Most heart attacks are caused by a clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). The clot usually forms in a coronary artery that has been previously narrowed from changes related to atherosclerosis . The atherosclerotic plaque (buildup) inside the arterial wall sometimes cracks, and this triggers the formation of a thrombus, or clot. A clot in the coronary artery interrupts the flow of blood and oxygen to the heart muscle, leading to the death of heart cells in that area. The damaged heart muscle permanently loses its ability to contract, and the remaining heart muscle needs to compensate for it. Rarely, sudden overwhelming stress can trigger a heart attack. It is difficult to estimate exactly how common heart attack is because many patients die before seeking medical help (perhaps as many as 200,000 to 300,000 in the United States per year). It is estimated that approximately 1 million patients visit the hospital each year with some type of MI as their principal diagnosis. The risk factors for coronary artery disease and heart attack include:

Smoking

Hypertension

(high blood pressure)

High-

fat diet

High blood cholesterol

(

LDL ) levels

Diabetes

Male gender

Age

Heredity

Newer risk factors for coronary artery disease have been identified over the past several years, including elevated homocysteine and C-reactive protein levels. Homocysteine levels can be treated with folic acid supplements in the diet. Studies are still ongoing about the practical value of these new factors. Heart attack accounts for 1 out of every 5 deaths. It is a major cause of sudden death in adults.

Signs and tests

Examination often reveals a rapid pulse . Blood pressure may be normal, high, or low. Listening to the chest with a stethoscope ( auscultation ) may show crackles in the lungs, heart murmur or other abnormal sounds. Heart attack and the extent of heart damage may also show on the following tests:

An electrocardiogram (

ECG ), single or repeated over several hours

Coronary angiography

Nuclear ventriculography (MUGA or RNV)

Echocardiography

The by-products of heart damage and factors indicating high risk for heart attack may show on the following tests:

Troponin I and troponin T

CK

and

CK-MB

Myoglobin - serum

Treatment

A heart attack is a medical emergency! Hospitalization is usually required for 1 to 14 days. Treatment may include intensive care. Continuous

ECG monitoring is started immediately, because life-threatening arrhythmias are the leading cause of death in the first few hours of a heart attack. The goals of treatment are to stop the progression of the heart attack, to reduce the demands on the heart so that it can heal, and to prevent complications. An intravenous line will be inserted to administer medications and fluids. Various monitoring devices may be necessary. A urinary catheter may be inserted to closely monitor fluid status. Oxygen is usually given, even if blood oxygen levels are normal. This makes oxygen readily available to the tissues of the body and reduces the workload of the heart. MEDICATIONS Morphine or morphine derivatives are potent analgesics , often given for pain. Sublingual (under the tongue) or intravenous (IV) nitrates such as nitroglycerin are also given for pain and to reduce the oxygen requirements of the heart. If the ECG recorded during chest pain shows a change called "ST-segment elevation," clot-dissolving (thrombolytic) therapy may be initiated within 6 hours of the chest pain onset. This initial therapy will be administered as an IV infusion of streptokinase or tissue plasminogen activator, and will be followed by an IV infusion of heparin. Heparin therapy will last for 48 to 72 hours. Additionally, warfarin may be prescribed to prevent further development of clots. Thrombolytic therapy is not appropriate for people who have had:

A major surgery, organ

biopsy , or major trauma within the past 6 weeks

Recent neurosurgery

Head trauma

within the past month

History of GI (gastrointestinal) bleed

Intracranial

tumor

Stroke

within the past 6 months

Current severe hypertension

Possible complications of thrombolytic therapy include bleeding and hemorrhage. A cornerstone of therapy for a heart attack is antiplatelet medication (a medication that can prevent platelet aggregation which is the initial event in the circulation leading to clot formation). One antiplatelet agent widely used is aspirin, given at a dose of 160 mg/day. Another antiplatelet medication in use is ticlopidine. More recently, a medication called clopidogrel has shown in clinical studies to be even more effective than aspirin to reduce the occurrence of new heart attacks. Other medications that may be prescribed include the following:

Beta-blockers, to reduce the workload of the heart

Glycoprotein IIb/IIIa inhibitors

Calcium channel blockers

Anti-arrhythmics

Diuretics.

In the first 24 hours of a heart attack that compromises the anterior wall of the heart or is complicated by heart failure, drugs called ACE inhibitors may be recommended. PROCEDURES Emergency coronary angioplasty may be required to open blocked coronary arteries. This procedure may be used instead of thrombolytic therapy, or in cases where such therapy is contraindicated. Often the re-opening of the coronary artery after angioplasty is ensured by implantation of a small device called a stent. Emergency coronary artery bypass surgery ( CABG ) may be required in some cases. Activity may be restricted initially, then gradually increased.

Support groups

The stress of illness can often be helped by joining a support group where members share common experiences and problems. See heart disease - support group .

Expectations (prognosis)

The expected outcome varies with the amount and location of damaged tissue. The outcome is worse if there is damage to the electrical conduction system (the impulses that guide heart contraction). Approximately one-third of cases are fatal. If the person is alive 2 hours after an attack, the probable outcome for survival is good, but may include complications. Uncomplicated cases may recover fully; heart attacks are not necessarily disabling. Usually the person can gradually resume normal activity and lifestyle, including sexual activity.

Complications

Arrhythmias

such as

ventricular tachycardia , ventricular fibrillation, heart blocks

Congestive heart failure

Cardiogenic shock

Infarct extension: extension of the amount of affected heart tissue

Pericarditis

Pulmonary embolism

Complications of treatment (For example, treatment with thrombolytic agents increases the risk of

bleeding during treatment.)

Calling your health care provider

Go to the emergency room or call your local emergency number (such as 911) if crushing chest pain or other symptoms suggestive of heart attack occur.

Prevention

Control cardiac risk factors whenever possible. Control blood pressure and total cholesterol levels. To help with cholesterol control, your doctor may prescribe a medication of the statins group (atorvastatin, simvastatin). You may also need to take aspririn or clopidogrel daily. Avoid smoking , modify diet if necessary (increase vegetables, vegetable oils, and fruits and decrease animal fats), control diabetes , and lose weight if obese . Exercise daily or several times a week by walking and including specific exercises to improve cardiovascular fitness. (Consult your health care provider first.) After a heart attack, follow-up care is important 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. Follow the exercise, diet, and medication regimen prescribed by your doctor.