**Question:** Abnormal increase in the amplitude of 'U' wave is seen with

A. Hyperkalemia
B. Hypokalemia
C. Hypoxia
D. Hypernatremia

**Correct Answer:** A. Hyperkalemia

**Core Concept:** The 'U' wave is a late, triangular deflection on the electrocardiogram (ECG) that is typically seen following the T wave. It is caused by the repolarization of the sinoatrial (SA) node, atrioventricular (AV) node, and ventricles. The amplitude of the U wave represents the degree of potassium ions' entrance into the cells during repolarization.

**Why the Correct Answer is Right:** An increase in the amplitude of the U wave indicates an abnormality in repolarization, which is primarily influenced by potassium levels in the blood. Hyperkalemia, a condition with elevated potassium levels, leads to increased potassium ions entering the cells during repolarization, resulting in a visible increase in the U wave amplitude.

**Why Each Wrong Option is Incorrect:**

**A. Hypokalemia:** Hypokalemia is a condition with decreased potassium levels. Hypokalemia would decrease the U wave amplitude due to less potassium entering the cells during repolarization. Thus, this option is incorrect.

**B. Hypoxia:** Hypoxia affects cardiac function indirectly by causing changes in heart rate, contractility, and conduction, but it does not directly impact the U wave amplitude. Therefore, this option is incorrect.

**C. Hypernatremia:** Hypernatremia refers to elevated sodium levels, which does not directly influence U wave amplitude as it affects ion concentrations in the extracellular space but not cellular potassium levels. This option is incorrect.

**D. Narrow QRS complex:** A narrow QRS complex indicates normal electrical conduction in the ventricles. However, the question specifically asks about the U wave, which is unrelated to QRS complex morphology. This option is incorrect.

**Clinical Pearl:** A high potassium level in the blood, as seen in hyperkalemia, can lead to cardiac arrhythmias and may cause a range of ECG changes, including widened QRS complex, flattened T wave, and increased U wave amplitude. Understanding these ECG changes can help in diagnosing hyperkalemia and guiding treatment decisions.