Heart attack

Definition

A heart attack, which is also called a myocardial infarction (MI), is the death or damage of part of the heart muscle because the supply of blood to the heart muscle is sharply reduced or stopped.

Description

A heart attack occurs when one or more of the coronary arteries that supply blood to the heart are completely blocked and blood to the heart muscle is cut off. The blockage is usually caused by athero-sclerosis , the build-up of plaque in artery walls, and/or by a blood clot in a coronary artery. Sometimes, a healthy or atherosclerotic coronary artery has a spasm and the blood flow to part of the heart decreases or stops, resulting in a heart attack.

Demographics

Generally, heart attacks occur in persons over age 40 and most are in those ages 50 to 70. Between the

ages of 40 to 65, more men than women suffer heart attacks; after age 65 the gender difference disappears.

Causes and symptoms

Heart attacks are generally caused by severe coronary artery disease. Most are caused by blood clots that form on atherosclerotic plaque, which impedes the supply of blood to part of the heart. A number of major and contributing risk factors increase the likelihood of developing coronary artery disease. Some of these risk factors can be modified, but others cannot. Persons with more risk factors are more likely to develop coronary artery disease.

Major risk factors

Major risk factors significantly increase the likelihood of developing coronary artery disease. Risk factors that cannot be changed include:

• Heredity. People whose parents have coronary artery disease, particularly those who develop it at younger ages, are more likely to be diagnosed with it.
• Gender. Men under the age of 60 years of age are more likely to have myocardial infarctions than women of the same age.
• Age. Men over age 45 and women over age 55 are considered at risk. Older adults (those over 65) are more likely to die as a result of a heart attack. Older women are twice as likely to die within a few weeks of a heart attack as men.

Major risk factors which can be changed are:

• Smoking greatly increases both the risk of developing coronary artery disease and the chance of dying from it. Smokers are more than twice as likely to have a heart attack. They are also more likely to die within an hour of a heart attack. Second-hand smoke may also increase risk.
• High cholesterol levels increase the risk of developing coronary artery disease. When combined with other factors, the risk is even greater. Low levels of HDL (high-density lipoprotein) increase the risk of coronary artery disease; highHDLprotects against it.
• High blood pressure makes the heart work harder, and over time, weakens it. When high blood pressure is combined with obesity, smoking, high cholesterol, or diabetes, the risk of heart attack or stroke increases.
• Sedentary lifestyle and lack of physical activity increase the risk of heart disease. Even modest physical activity is beneficial if done regularly.

QUESTIONS TO ASK YOUR DOCTOR

• How can I help to prevent a second heart attack?
• Is exercise safe after a heart attack?
• Is sexual activity safe after having a heart attack?

Contributing risk factors

Contributing risk factors have been linked to coronary artery disease, but their significance and prevalence are not known yet. Contributing risk factors are:

• Diabetes increases the risk of developing heart disease.
• Obesity increases the strain on the heart muscle and increases the risk of developing heart disease, even if no other risk factors are present. Obesity increases both blood pressure and blood cholesterol, and can lead to diabetes.
• Stress and anger can produce physiological changes that contribute to the development of coronary artery disease. Stress increases heart rate and blood pressure, and can injure the lining of the arteries. Evidence shows that anger increases the risk of dying from heart disease and more than doubles the risk of having a heart attack right after an episode of anger.

More than 60% of patients experience symptoms before the heart attack occurs. These symptoms may occur days or weeks before the heart attack. Common symptoms include:

• Uncomfortable pressure, fullness, heaviness, squeezing, or pain in the center of the chest. The sensation lasts more than a few minutes, or may go away and return.
• Pain that spreads to the shoulders, neck, left arm, or jaw.
• Chest discomfort accompanied by lightheadedness, fainting, sweating, nausea, or shortness of breath.

All of these symptoms do not necessarily occur with every heart attack. Sometimes, symptoms disappear and then reappear. Persons with any of these symptoms should immediately call an emergency rescue service or be driven to the nearest hospital with a 24-hour cardiac care unit, whichever is quicker.

Diagnosis

Experienced emergency medical personnel confirm the diagnosis of heart attack by taking a thorough history, checking heart rate and blood pressure , performing an electrocardiogram (ECG), and drawing a blood sample. The ECG shows which coronary artery is blocked. The blood test detects the leak of enzymes or other biochemical markers from damaged cells in the heart muscle.

Treatment

Treatment usually begins in the emergency department with thrombolytic agents, aspirin , oxygen, and beta-blockers. Oxygen eases the heart's workload and can help patients breathe easier. If oxygen is administered within hours of the heart attack, it also may help limit damage to the heart. Subsequent treatment includes close monitoring; nitrates and morphine if needed; electric shock; drug therapy; revascularization procedures; coronary angioplasty ; and coronary artery bypass surgery.

Patients with complications such as arrhythmias, congestive heart failure , and blood pressure problems require additional treatment. A defibrillator may be used to restore a normal rhythm. A temporary pacemaker may be inserted to correct a slow heart rate. Ace inhibitors may be used to treat congestive heart failure.

Drugs to and limit damage to the heart include thrombolytics, aspirin, anticoagulants, painkillers, and tranquilizers, beta-blockers, ace-inhibitors, nitrates, anti-arrhthythmics (rhythm-stabilizing) drugs, and diuretics . Thrombolytics, used to limit damage to the heart, work only if given within 6–12 hours of the onset (when the chest pain began) of the heart attack. Thrombolytic drugs act by dissolving the blood clot that is blocking the acutely occluded coronary artery. They increase the likelihood of survival when given as soon as possible after the heart attack.

Nutrition/Dietetic concerns

Maintaining a healthy body weight is vital for heart health. People who are 20% or more over their ideal body weight are at increased risk of developing coronary artery disease. Losing weight can help reduce total and LDL cholesterol, reduce triglycerides, and boost relative levels of HDL cholesterol. It may also reduce blood pressure.

Prognosis

The aftermath of a myocardial infarction is often severe. Thirty percent of patients die as a result of a heart attack. People who survive have a chance of sudden death that is four to six times greater than others and a chance of illness and death that is two to nine times greater. In general, the smaller the amount of heart muscle affected, the better the prognosis. Other factors that affect prognosis include age and the presence of other coexisting illnesses such as diabetes or high blood pressure. The outlook also depends on whether patients adhere to medical treatment and take action to eliminate or reduce modifiable risk factors.

KEY TERMS

Angina —Chest pain that occurs when diseased blood vessels restrict the flow of blood to the heart. Angina is often the first symptom of coronary artery disease.

Atherosclerosis —A process in which the walls of the coronary arteries thicken due to the accumulation of plaque in the blood vessels. Atherosclerosis is the cause of coronary artery disease.

Coronary arteries —The two arteries that provide blood to the heart. The coronary arteries surround the heart like a crown, coming out of the aorta, arching down over the top of the heart, and dividing into two branches. These are the arteries where coronary artery disease occurs.

Myocardial infarction —The medical, technical term for heart attack. Myocardial means heart muscle and infarction means death of tissue from lack of oxygen.

Plaque —A deposit of fatty and other substances that accumulate in the lining of the artery wall.

Prevention

Many heart attacks can be prevented through a healthy lifestyle, which can reduce the risk of developing heart disease . For patients who have already had a heart attack, a healthy lifestyle can prevent another heart attack. A heart healthy lifestyle includes a low-fat diet , regular exercise , maintaining a healthy weight, no smoking , moderate drinking, controlling high blood pressure, and managing stress .

Daily aspirin therapy has been proven to help prevent blood clots associated with atherosclerosis. It can also prevent heart attacks from recurring, prevent them from being fatal, and reduce the risk of strokes.

Caregiver concerns

Depression is a common repercussion of a heart attack, as well as a common side effect of medications used to treat patients who have suffered heart attacks. Care givers and family members also should be sensitive to the fact that diminished tolerance for physical exertion can limit a heart attack patient's ability to participate in physically demanding activities. Many patients are fearful about safely engaging in sexual activity after suffering a heart attack and may benefit from counseling to help allay their fears.

Resources

BOOKS

Zipes DP, Libby P, Bonow RO, Braunwald E, eds. Braunwald's heart disease: a textbook of cardiovascular medicine, 7th ed. Philadelphia: Saunders, 2005.

PERIODICALS

AHA; ACC; National Heart, Lung, and Blood Institute; Smith SC Jr, Allen J, Blair SN, et al. “AHA/ACC guidelines for secondary prevention for patients with coronary and other atherosclerotic vascular disease:2006 update". Endorsed by the National Heart, Lung, and Blood Institute. Journal of the American College Cardiology vol.16, no.10, May 2006

Boersma E, Mercado N, Poldermans D, et al. “Acute myocardial infarction.” Lancet vol.361, no.9374, June 14, 2003

ORGANIZATIONS

American Heart Association, 7272 Greenville Avenue, Dallas, TX, 75231, 301 592-8573, 800 242-8721, 301 592-8563, http://www.americanheart.org.

National Heart, Lung, and Blood Institute, PO Box 30105, Bethesda, MD, 20824-0105, 301 592-8573, 800 242 8721, 301 592-8563, http://www.nhlbi.nih.gov.

Barbara Wexler MPH