Early in STEMI, what ECG change may appear as prominent T waves before ST elevation?

Prepare for the Cleveland Clinic EKG Test with flashcards and multiple choice questions. Gain insights with hints and explanations. Ace your exam today!

Early in STEMI, the heart’s ischemic injury causes changes in repolarization that show up as hyperacute T waves—tall, broad, and prominent T waves in the leads facing the affected area. These are among the very first ECG signs of evolving infarction and can appear before any ST-segment elevation is seen. The exaggerated T waves reflect acute injury currents as cells become ischemic and edema develops, altering how the myocardium repolarizes. As infarction progresses, ST elevation appears next, and later on Q waves may develop indicating necrosis. The other changes listed—deep T waves, pathologic Q waves, and QT prolongation—are not typical early markers before ST changes in acute STEMI: deep T waves tend to occur later or in different patterns, Q waves indicate established infarction, and QT prolongation is not a defining early feature of STEMI. Hyperacute T waves are the best answer because they capture the earliest electrical signature of evolving myocardial ischemia.