Which change on an ECG might indicate ischemia?

Depressed ST segments are often used as an indicator of ischemia on an ECG. Ischemia, which refers to a reduced blood flow to heart muscle, can cause a deviation in the normal ST segment of the ECG trace. Specifically, when there is insufficient blood supply, this can lead to changes in the electrical activity of the heart, manifesting as ST segment depression, particularly during exertion or under stress conditions.

In the context of ischemia, the heart muscle may not receive enough oxygen, which affects the repolarization phase of the cardiac cycle. This is reflected by the ST segment deviating downwards from the baseline during the ECG reading. Analyzing these changes can become crucial for early detection of potential coronary artery issues.

The other options provided describe different cardiac issues that may not specifically indicate ischemia. Elevated ST segments are typically associated with conditions such as myocardial infarction. A shortened PR interval may suggest a conduction disturbance but does not directly relate to ischemic conditions. Lastly, a prolonged QT interval is often linked with arrhythmias or electrolyte imbalances, which are also not indicative of ischemia. Each of these options points to different electrical abnormalities but does not reflect the hallmark sign of ischemia that ST segment depression does.