Which statement describes a normal ST segment?

• A. It is usually elevated
• B. It is usually isoelectric
• C. It always follows a QRS complex
• D. It is always depressed

Answer: (B)

A normal ST segment is characterized as isoelectric, meaning it typically lies on the baseline level of the ECG tracing, indicating that there is no net electrical activity occurring in the heart during this phase. This segment follows the QRS complex and precedes the T wave in a typical ECG, representing the period between ventricular depolarization and repolarization.

An elevated ST segment often indicates potential problems, such as myocardial infarction or other cardiac complications, whereas a depressed ST segment can suggest issues like ischemia. Furthermore, while the ST segment does indeed follow the QRS complex as a general rule, it is not exclusively defined by this characteristic. The defining feature of a normal ST segment is its isoelectric nature, which reflects healthy heart electrical activity. This clarity about the normal state is essential for interpreting ECG readings effectively in clinical settings.