Harvard Heart Letter

Redefining myocardial infarction

The latest definition should mean fewer missed heart attacks.

A heart attack — myocardial infarction in doctor-speak — isn't an instantly recognizable event. Some attacks are so small they pass almost unnoticed, written off as indigestion or the flu. Others are major catastrophes, causing death or long-lasting disability. What they all have in common is the death of heart muscle caused by a lack of blood flow to part of the heart.

In the 1950s, doctors had to rely on a person's symptoms and sometimes hard-to-interpret changes on an electrocardiogram to determine if a heart attack was under way. As researchers learned how to detect the chemical signature of dying heart cells, blood tests have become an important part of the diagnosis. The early blood markers were signs of general trouble in and around the heart. The one preferred today, called troponin, is the best red flag so far. Troponin is a protein complex found almost exclusively in heart and skeletal muscle cells. Its sudden release into the bloodstream signals damage to the heart muscle. It is also released earlier and more readily than the proteins that were previously used to help diagnose a myocardial infarction.

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