A zone of ischemia typically produces what variation in the ST segment?

• A. Elevation
• B. Depression
• C. No change
• D. Inversion

Answer: (B)

When there is a zone of ischemia in the heart muscle, it typically manifests as a depression in the ST segment on the ECG. This depression occurs because ischemic tissue is unable to depolarize and repolarize normally, leading to a distortion in the electrical activity recorded on the ECG. The changes reflect an imbalance in the ionic environment of the myocardial cells, which affects their electrical stability.

The presence of ST segment depression is indicative of subendocardial ischemia, which may occur during situations such as angina or stress testing. This specific alteration in the ECG can be an important diagnostic marker for coronary artery disease or impending myocardial infarction. By identifying these ST segment changes, healthcare providers can assess the severity and extent of ischemic heart conditions, allowing for appropriate management and intervention.

In contrast, ST segment elevation is often associated with acute myocardial infarction, while no change or inversion might signify different underlying cardiac conditions, making the identification of ST segment depression a vital tool in ECG interpretation related to ischemia.