Which of the following is NOT a cause of ST segment changes?

The correct answer focuses on the relationship between anatomical or structural heart conditions and their direct effects on the ST segment of an EKG. ST segment changes are primarily indicative of acute pathophysiological processes, such as ischemia, infarction, or an electrolyte imbalance.

Myocardial infarction is well-known for causing significant ST segment deviations, particularly ST elevation or depression, as it represents acute myocardial ischemia. Electrolyte imbalances, such as changes in potassium or calcium levels, can also lead to ST segment changes due to their direct effects on cardiac electrical conduction. Pulmonary embolism, while primarily a respiratory issue, can lead to strain on the right side of the heart, which may manifest as ST changes.

In contrast, cardiac stenosis, which refers to the narrowing of heart valves, typically presents with symptoms related to heart failure rather than direct changes in the ST segment. Although it may lead to chronic pressures and compromises in cardiac function, it does not directly cause the acute electrical changes in the heart that would be reflected in the ST segment on an EKG. Understanding this distinction helps clarify why the other options are associated with ST segment changes, while cardiac stenosis is not.