A 60-year-old woman on long-term diuretic therapy presents with muscle weakness. Her ECG shows prominent U waves and ST-segment depression. Which serum electrolyte abnormality is most directly responsible for these ECG changes?
- A Hyperkalemia
- B Hypercalcemia
- C Hypokalemia ✓
- D Hypocalcemia
Correct answer: C. Hypokalemia
Explanation
Hypokalemia classically causes ST-segment depression, flattened T waves, and prominent U waves, often leading to muscle weakness. Hyperkalemia causes peaked T waves and widened QRS complexes. Hypercalcemia shortens the QT interval, while hypocalcemia prolongs it. Diuretic use is a classic cause of hypokalemia.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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