ACLS Cardiac Arrest Practice Test

Which electrolyte abnormality is associated with prominent U waves on ECG?

Hyperkalemia Hypokalemia Hyponatremia Hypercalcemia

Correct Answer:

Hypokalemia

Explanation:

Prominent U waves on ECG are most characteristic of low potassium. When potassium levels fall, the outward K+ current during repolarization decreases, prolonging the late phase of ventricular repolarization. This creates a small, extra deflection after the T wave—the U wave—best seen in the precordial leads (often V2–V4). Along with U waves, hypokalemia commonly shows flattened or inverted T waves and ST-segment depression, and can predispose to arrhythmias. In contrast, hyperkalemia tends to produce tall, peaked T waves with widened QRS and eventually a sine-wave pattern, not prominent U waves. Hyponatremia and hypercalcemia have different ECG patterns that do not feature prominent U waves as a classic finding.

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