**Question:** What ECG finding is shown here?

A. ST elevation
B. ST depression
C. Sinus tachycardia
D. Atrial fibrillation

**Correct Answer:** B. ST depression

**Core Concept:** Electrocardiogram (ECG) is a non-invasive diagnostic tool used to evaluate the electrical activity of the heart and detect abnormalities in cardiac function. Changes in the ST segment represent myocardial ischemia, infarction, or dysfunction.

**Why the Correct Answer is Right:** ST depression is a change in the ST segment on an ECG, where the ST segment moves below the horizontal line of the isoelectric baseline. This finding is associated with myocardial ischemia or infarction, where oxygen demand exceeds the supply to the heart muscle.

**Why Each Wrong Option is Incorrect:**

A. ST elevation: This refers to the ST segment moving above the isoelectric line, indicating myocardial ischemia or infarction. This is the correct answer for ST elevation, not depression.

B. Sinus tachycardia: This refers to an increased heart rate, not a change in the ST segment. It is unrelated to the ECG findings shown.

C. Atrial fibrillation: This refers to an abnormal heart rhythm, not a change in the ST segment. It is unrelated to the ECG findings shown.

**Clinical Pearl:** ST depression is a crucial ECG finding in diagnosing acute myocardial infarction (heart attack) and guiding appropriate medical management. It is essential for medical practitioners to interpret ECG findings accurately and promptly to provide optimal patient care.