About Acute Myocardial Infarction

Acute myocardial infarctions (AMI), also known as heart attacks, occur in over 1.1 million Americans each year, particularly in seniors. AMI is the leading cause of hospitalizations in patients over 65. Almost two-thirds of patients do not make a complete recovery from AMI. Even if a patient lives through an AMI, the risk of a related illness or death is two to nine times greater. According to the Maryland vital statistics report, more than 12,000 people in Maryland died from diseases of the heart in 2003.

Read on for more information, or click on a topic in the list:

What is AMI?
What are the symptoms?
What are the causes?
How is it diagnosed?
What are the effects of AMI?
How is it treated?

AMI occurs when a blockage in an artery interrupts the flow of blood to the heart. A lack of blood and oxygen causes heart cells to die.

The atria receive blood from the body. The ventricles collect blood from the atria and pump it out of the heart. AMI can occur in any of these chambers, but they most often occur in the left ventricle.

The first symptom of AMI may be a deep pain in the middle of the chest behind the breastbone. Other symptoms may occur suddenly or develop gradually. Sometimes symptoms occur days to weeks before the event that blocks the flow of blood. Symptoms include:

• Chest pain, called unstable angina, not as common in women  
• Pressure in the chest, described as “crushing,” also not as common in women
• A pain that moves to the back, jaw, or left arm
• Shortness of breath
• Fatigue
• Abdominal pain (an “inferior heart attack”)
• Nausea and vomiting
• Very mild discomfort or no symptoms (a “silent heart attack”)

AMI can be caused by coronary artery disease. When a patient with coronary artery disease has an AMI, the blockage in the flow of blood is caused by blood platelets and a tear in the fatty buildup. When the blood platelets find the tear in the fatty buildup, they make a clot around it. The combination of fatty buildup and the blood clot blocks the flow of blood and chokes off oxygen to the heart.

Hypertension, can also lead to AMI when blood flow pushes too strongly against artery walls and causes fatty buildup. High cholesterol levels, tobacco use, and physical inactivity are also major factors that contribute to AMI.

Other less common causes of AMI include cocaine use and a spasm of the coronary arteries. A blockage occurs during these events because the artery suddenly contracts and stops blood flow.

A doctor usually diagnoses AMI based on the medical history of the patient. The diagnosis is confirmed by any of the following tests:

• Electrocardiograms (ECG)—This test detects the patient’s heartbeat using electrical signals from the heart.

• Echocardiograms—This test uses sound waves to record blood flow in the heart. The sound waves are sent through the patient’s skin or through the esophagus.

• Cardiac catheterization—A doctor passes contrast material through the coronary arteries or chambers of the heart.

• Blood tests—Blood tests may detect signs of changes in enzymes in the blood that occur when the heart is damaged or the presence of troponins to help detect injury to the heart muscle.

Damage to the heart from AMI leads to heart failure in two-thirds of patients hospitalized for AMI. Arrhythmias are another possible complication of AMI.

AMI often can result in left ventricular systolic dysfunction (LVSD). As a result, fluid backs up and accumulates in the lungs, causing breathing difficulties. Hospitals should always check the left side of the heart for weakness in AMI patients.

The Centers for Medicare & Medicaid Services and Joint Commission for the Accreditation of Healthcare Organizations have determined that the following treatments are indicators of quality care for AMI:

• Aspirin within 24 hours
• ACE inhibitor
• Beta blocker
• Advice for smokers on how to stop smoking
• Aspirin at discharge

Hospital Leaders can find more information about treating AMI in Best Practices for AMI.