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How can an electrocardiogram help detect a myocardial infarction?

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The role of coronary artery disease in heart attack — cardiovascular disease This micrograph shows a cross section of a coronary artery narrowed by an atherosclerotic plaque (purplish matter inside the artery). Most heart attacks are caused by the rupture of an atherosclerotic plaque, which triggers the formation of a clot that abruptly blocks blood flow to part of the heart muscle.

An electrocardiogram (ECG or EKG) detects a myocardial infarction—commonly known as a heart attack—by recording the electrical activity of the heart muscle through electrodes placed on the limbs and chest.21

Because a myocardial infarction involves the death of heart muscle tissue (necrosis), it disrupts the normal electrical impulses generated during a heartbeat. In most instances, this damage produces distinct and characteristic abnormalities in the ECG tracing at the onset of the event. These deviations from the normal pattern—which typically shows specific P, Q, R, S, and T waves—provide clinicians with vital diagnostic information regarding the condition and performance of the heart.231

It is important to note, however, that ECG results are not infallible; in some cases, the abnormalities may be less characteristic or even absent during an infarction. Therefore, while the electrocardiogram is a primary tool for diagnosing acute and prior heart attacks, it is often used in conjunction with other clinical assessments.32