Which of the following is a major sign of hypokalemia?

• A. Tall, peaked T waves
• B. Narrow QRS complex
• C. Flattened T waves
• D. Shortened QT interval

Answer: (C)

Potassium levels shape how ventricular cells repolarize, and the ECG reflects that process. When potassium is low, the repolarization current is reduced, so the T wave loses amplitude and becomes flattened. This flattening is the hallmark sign you look for with hypokalemia. You may also see U waves after the T wave, which result from delayed repolarization of some ventricular tissue. The other options point to different electrolyte problems or non-specific changes: tall, peaked T waves occur with hyperkalemia; a narrow QRS complex isn’t a defining feature of potassium disturbances; and a shortened QT interval isn’t typical for hypokalemia ( QT is often prolonged due to prolonged repolarization).