**Core Concept:** Hypokalaemia is a condition characterized by low levels of potassium ions (K+) in the blood, which can lead to disruption of cardiac, skeletal, and renal functions. Potassium plays a crucial role in maintaining the resting membrane potential, excitability, and contraction of cells.

**Why the Correct Answer is Right:** The question is asking about the ECG changes that are not seen in hypokalaemia. Correct ECG changes in hypokalaemia include T-wave inversion, widening of QRS complex, and prolonged PR interval. However, the changes in ST segment elevation are not typically seen in hypokalaemia.

**Why Each Wrong Option is Incorrect:**

A. T-wave inversion: This is a common finding in hypokalaemia, reflecting the depolarization abnormalities in cardiac myocytes.
B. Widening of QRS complex: This represents increased sodium influx into cardiac myocytes, which is also seen in hypokalaemia.
C. Prolonged PR interval: This is a result of slowed conduction in the atrioventricular (AV) node, not specifically related to potassium levels.
D. ST segment depression: This is a common finding in ischemia and infarction, not typically seen in hypokalaemia.

**Clinical Pearl / High-Yield Fact:** Hypokalaemia should be suspected in patients with neuromuscular symptoms (weakness, tetany, cramps) and ECG changes (T-wave inversion, widened QRS complex) in the absence of ST depression. Correction of hypokalaemia can have significant clinical benefits, including relief of symptoms and normalization of ECG findings.

**Correct Answer:** D. ST segment depression

While hypokalaemia can lead to QRS complex widening and T-wave inversion, ST segment depression is a more specific ECG finding that is less likely to occur in hypokalaemia. In hypokalaemia, the QRS complex widening reflects increased sodium influx into cardiac myocytes, while ST segment depression is more commonly associated with ischemia and infarction.