**Question:** Hypokalemia ECG changes-

A. Tall U waves
B. Flattened T waves
C. Sweeping U waves
D. Absent U waves

**Correct Answer:** A. Tall U waves

**Core Concept:** Hypokalemia refers to low potassium levels in the blood, which can lead to disruption of the normal electrical activity of the heart. Potassium plays a crucial role in maintaining the resting membrane potential of cardiac cells and in the generation of action potentials.

**Why the Correct Answer is Right:** In hypokalemia, the decrease in extracellular potassium levels can affect the normal functioning of cardiac muscle cells. Specifically, the reduction in potassium causes a decline in the amplitude of the U waves on an electrocardiogram (ECG). U waves are typically seen in the terminal portion of the QRS complex and represent the repolarization phase of cardiac action potentials. When potassium levels are low, the amplitude of these U waves decreases, leading to taller U waves on the ECG.

**Why Each Wrong Option is Incorrect:**

B. Flattened T waves: Hypokalemia primarily affects the U waves, not T waves. Flattened T waves may be seen in other conditions such as myocardial infarction, atrial fibrillation, or QT interval prolongation.

C. Sweeping U waves: This term is incorrect. The correct term is "tall U waves." Additionally, sweeping U waves would indicate hyperkalemia, not hypokalemia.

D. Absent U waves: This is incorrect as well. In hypokalemia, the U waves become taller, not absent. Absent U waves would indicate hyperkalemia or other conditions affecting the repolarization phase of cardiac action potentials.

**Clinical Pearl:** Hypokalemia can lead to cardiac arrhythmias, including Torsades de Pointes, a potentially life-threatening ventricular arrhythmia. Monitoring potassium levels in patients with suspected hypokalemia is essential, as appropriate management may prevent severe complications.