An electrocardiogram shows a prominent U-wave. Which electrolyte imbalance is most likely responsible?

An electrocardiogram shows a prominent U-wave. Which electrolyte imbalance is most likely responsible?

• A. Hypermagnesemia
• B. Hypokalemia
• C. Hyponatremia
• D. Hypocalcemia

Answer: (B)

A prominent U-wave on an ECG points to low potassium levels in the blood. The U-wave reflects late ventricular repolarization, and when extracellular potassium is reduced, this late repolarization becomes exaggerated, producing a noticeable U-wave. In hypokalemia you also often see flattened or inverted T waves and ST-segment depression. Other choices don’t fit this pattern: high magnesium can cause conduction abnormalities but not the classic U-wave prominence associated with low potassium; hyponatremia mainly affects brain and fluid balance rather than producing a characteristic U-wave; low calcium lengthens the QT interval by prolonging the plateau phase of the action potential rather than producing prominent U-waves. So the electrolyte imbalance most likely responsible is hypokalemia.

A prominent U-wave on an ECG points to low potassium levels in the blood. The U-wave reflects late ventricular repolarization, and when extracellular potassium is reduced, this late repolarization becomes exaggerated, producing a noticeable U-wave. In hypokalemia you also often see flattened or inverted T waves and ST-segment depression.

Other choices don’t fit this pattern: high magnesium can cause conduction abnormalities but not the classic U-wave prominence associated with low potassium; hyponatremia mainly affects brain and fluid balance rather than producing a characteristic U-wave; low calcium lengthens the QT interval by prolonging the plateau phase of the action potential rather than producing prominent U-waves.

So the electrolyte imbalance most likely responsible is hypokalemia.