Which ECG finding is indicative of a myocardial infarction?

The presence of an elevated ST segment on an electrocardiogram (ECG) is a critical marker for myocardial infarction (MI). This finding is associated with the acute phase of an MI, particularly in cases of ST-segment elevation myocardial infarction (STEMI). When ischemia occurs due to inadequate blood flow, reperfusion leads to cellular injury, which manifests as changes in the heart's electrical activity.

An elevated ST segment represents a pathophysiological response to myocardial injury, indicating that there is significant damage to the myocardial tissue. This is often accompanied by other changes, such as the presence of abnormal Q waves or T wave inversions, but the ST segment elevation is specifically indicative of an ongoing acute ischemic event.

In contrast, flat T waves can reflect various conditions but are not explicitly diagnostic of myocardial infarction. A prolonged QT interval is often associated with electrolyte imbalances or certain medications, and while a wide QRS complex can indicate various cardiac conditions like bundle branch blocks, it does not specifically signal myocardial infarction. Thus, the elevated ST segment is the hallmark finding that clinicians look for to confirm an ongoing myocardial infarction.