How is myocardial ischemia often indicated on the ECG?

Myocardial ischemia is typically indicated on an ECG by a depressed ST segment. This phenomenon occurs because ischemia leads to a disturbance in the electrical activity of the heart. When the heart muscle does not receive enough oxygen-rich blood, the normal repolarization process is altered, leading to the characteristic downward shift of the ST segment on the ECG tracing.

In cases of ischemia, especially during stress or the presence of a blockage, the myocardial tissue can become less electrically responsive, which is reflected as a depression in the ST segment. This finding is clinically significant and alerts healthcare professionals to the possibility of reduced blood flow to the heart, which may require further investigation or intervention.

Other options like elevated ST segments are more indicative of myocardial injury or infarction rather than ischemia alone. A widened QRS complex may suggest conduction abnormalities rather than ischemia, and absent T waves could indicate other conditions, such as severe ischemia or effects from prior myocardial infarction, rather than being a direct indicator of ischemia. Hence, depressed ST segment is the clearest reflection of myocardial ischemia on an ECG.