Heart attack (myocardial infarction) overview

Myocardial infarction, commonly known as a heart attack, is essentially synonymous with the acute coronary syndrome spectrum classification for STEMI. It occurs when a large part of the heart muscle is deprived of oxygen after a sudden and complete, or nearly complete, blockage of a coronary artery. If the flow of blood is not restored quickly, the affected heart muscle becomes damaged from lack of oxygen and begins to die.

The patient will most likely complain of chest pain, nausea, sweating, and difficulty breathing. However, as many as 20% of myocardial infarctions may go unrecognized because they are silent and do not cause any pain.

Myocardial infarction is a medical emergency. Among those patients who actually survive long enough to make it to the hospital, about 10% will die within a year. Approximately half of all deaths from a myocardial infarction occur within the first 3 to 4 hours after the onset of symptoms. The rapid reestablishment of coronary circulation is critical to preventing or minimizing damage to the myocardium. In fact, prompt reperfusion may limit the extent of the infarction and minimize the risk of major cardiac complications, such as pump failure and abnormal heart rhythms. Thus, patients who are having a myocardial infarction are frequently given aspirin to thin the blood, or antithrombolytic drugs, such as Heparin, to prevent the formation of additional clots.

Diagnoses of myocardial infarction is based on ECG findings and blood tests to evaluate the presence of myocardial proteins and enzymes which are released into the circulation when myocardial cells die. Although the ECG usually reveals an ST segment elevation, occasionally a negative result can be obtained. Therefore, serial ECG tracing are important for the diagnosis of acute myocardial infarction. Blood tests will show cardiac biomarkers, or enzymes, within 12 hours of heart muscle damage.

Review Date:7/14/2024
Reviewed By:Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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