Depressed T waves on an ECG most commonly indicate which electrolyte abnormality?

• A. Hyperkalemia
• B. Hypokalemia
• C. Hypercalcemia
• D. Hypermagnesemia

Answer: (B)

Depressed or flattened T waves on the ECG reflect changes in ventricular repolarization caused by low potassium. When potassium levels fall, the repolarization phase is altered, leading to reduced T-wave amplitude and often the appearance of U waves, ST depression, and other related changes. This pattern is characteristic of hypokalemia, making it the best explanation for depressed T waves.

In contrast, high potassium causes tall, peaked T waves with quicker progression to other changes like widened QRS, hypercalcemia tends to shorten the QT interval, and hypermagnesemia can slow conduction with different ECG signs. Those patterns do not center on depressed T waves, so hypokalemia most fits the finding.