Myocardial infarction is a heart attack. It occurs when there is sudden, complete blockage of blood flow to a portion of heart muscle. Myocardial infarction is one of the most common diseases in the U.S. and causes a large number of deaths every year.

Also in this article: What Happens After Myocardial Infarction? What Are the Risk Factors for a Heart Attack? What Are the Symptoms? How Is It Diagnosed? How Is It Treated? What Happens After Hospital Discharge?

Coronary arteries bring blood, oxygen, and nourishment to the heart muscle. A heart attack starts when the flow of blood through a coronary artery is blocked. This blockage is usually caused by a clot (thrombus) that forms in a coronary artery in the area of an atherosclerotic plaque. An atherosclerotic plaque, made up of some types of blood cells, cholesterol, and other fatty substances, develops in the wall of the coronary artery. It may take years to form but causes the artery to become narrowed. The plaque may break (rupture) even if it is not completely blocking the flow of blood through the artery. The reason the plaque breaks open is unknown. When the plaque ruptures, a blood clot forms at the site of the rupture.

The blood clot grows quickly and completely blocks blood flow through the coronary artery. The lack of oxygen-carrying blood to the heart muscle results in chest pain and loss of the muscle's ability to squeeze. If the lack of blood continues for more than a few minutes, the muscle cells will die.

Much of what happens depends on the size of the dead heart muscle (infarct) and where in the heart it is located. If the damaged area is small, recovery is usually fast with few or no problems. If the area of heart muscle involved is large, the loss of normal heart pumping ability may cause low blood pressure, shock, or congestive heart failure. (For more information, see Cardiogenic Shock.)

Recovery will take a long time and death may occur. In the early stages of a heart attack, the dead heart muscle is likely to cause abnormal heart rhythms that can lead to sudden death. Unlike a broken arm or leg, the heart cannot be kept from moving in a cast or sling during recovery from a heart attack. It must continue to pump. Infarction causes temporary softening and weakness of the heart muscle. During the first few days after a heart attack, this weakness may become so severe that the weakened heart muscle bursts (ruptures). Most such ruptures end in death. Fortunately, they are rare.

The body heals the heart damage by forming a scar, just as in any other tissue. Healing is usually complete in 4 to 8 weeks.

The risk factors for heart attack are well known. Cigarette smoking causes many deaths from myocardial infarction and other heart diseases. Smoking causes almost half of the heart attacks of women under age 55. Stopping smoking can greatly reduce your chances of having a heart attack.

Heart attacks tend to run in families. Other risk factors include high blood pressure, high cholesterol, and diabetes. Most of these risk factors can be treated with medication and diet. With early treatment, heart attacks associated by these risk factors can usually be avoided or delayed.

Severe chest pain or pressure is the most noticeable symptom. The pain may be in the front or back of your chest and often is felt in the left arm. Sometimes pain occurs in the neck, jaw, or upper back. You may also sweat and feel weak. The pain usually lasts longer than 30 minutes. By that time, the pain has brought most people to a hospital or a doctor's office.

Your doctor will most likely be able to make a quick diagnosis by taking your electrocardiogram, which will show damage to the heart. An electrocardiogram records the electrical activity of the heart. (For more information, see Electrocardiogram.)

Sometimes, your blood will need to be tested. These blood tests determine whether heart muscle tissue has been destroyed. The results may not be available for several hours.

The aim of treatment is to restore blood flow through your coronary artery as quickly as possible. Drugs called thrombolytics are given through your vein as soon as you are diagnosed with a heart attack. They are usually started in the emergency room of a hospital. If given soon enough, these drugs usually dissolve the blood clot blocking the coronary artery and allow fresh blood to flow to the heart muscle. Thrombolytics are successful about 85% of the time. You will also be given some aspirin to chew.

While the thrombolytics are taking effect, you will be admitted to the intensive care unit or coronary care unit (ICU/CCU). Your blood pressure and electrocardiogram will be watched carefully. Any heart rhythm problems that arise can be treated quickly. Drugs called beta blockers are started and will be continued after you leave the hospital. ACE inhibitors, drugs that limit heart muscle damage, will also be started.

In some cases, your doctor may decide to use balloon angioplasty to quickly open a blocked artery. The angioplasty treatment involves placing a tube (catheter) with a deflated balloon at its tip in the blocked area. The balloon is inflated and the artery opened. (For more information, see Percutaneous Transluminal Coronary Angioplasty.)

Heart rhythm abnormalities are treated with medicines. A temporary cardiac pacemaker is sometimes required. A temporary cardiac pacemaker is a device that helps the heart to beat normally until it can recover on its own. Permanent cardiac pacemakers are rarely needed.

Your hospital stay usually lasts 3 to 10 days and starts with 1 to 3 days in the ICU/CCU. Cardiac rehabilitation, a program of exercise and education for people who have heart illnesses, takes up the rest of the time. The program starts in the hospital with a progressive exercise program and counseling about any lifestyle or diet changes that need to be made. Rehabilitation helps people to resume normal activity as quickly as possible. (For more information, see Cardiac Rehabilitation.)

A low-level exercise treadmill test is usually done just before you leave the hospital. This test helps your doctor find out if you are at increased risk for further problems. It also helps your doctor to recommend exercises for you. Your doctor will schedule office visits for you and follow the progress of your recovery to see if anything else (such as bypass surgery or angioplasty) needs to be done. Usually, you can expect to return to work or your ordinary activities within 8 weeks of your heart attack.

Written by Donald L. Warkentin, M.D. Published by iMcKesson Clinical Reference Products. Copyright © 1999-2001 iMcKesson LLC. All rights reserved.