Which ECG changes are commonly associated with hypokalemia?

Which ECG changes are commonly associated with hypokalemia?

• A. Peaked T waves or ST segment elevation with shortened QT interval.
• B. Flat T waves or ST depression with U waves, prolongation of QT interval.
• C. Widened QRS with sine-wave pattern.
• D. Pathologic Q waves with ST elevation in all leads.

Answer: (B)

Potassium levels directly shape how the heart’s electrical system repolarizes. When potassium is low, repolarization is slowed, which lengthens the QT interval and produces distinctive changes on the ECG: T waves become flat or inverted, the ST segment may be depressed, U waves appear after the T wave, and the overall QT interval is prolonged. This combination—flat T waves or ST depression with prominent U waves and a prolonged QT—is classic for hypokalemia and reflects the heart’s delayed repolarization. Why other patterns don’t fit hypokalemia: patterns with peaked T waves and ST elevation with a shortened QT point to hyperkalemia, not hypokalemia. A sine-wave pattern with a widened QRS indicates severe hyperkalemia. Pathologic Q waves with widespread ST elevation suggests a myocardial infarction, not electrolyte-related changes. So the description of flat T waves or ST depression with U waves and prolonged QT best matches hypokalemia.

Potassium levels directly shape how the heart’s electrical system repolarizes. When potassium is low, repolarization is slowed, which lengthens the QT interval and produces distinctive changes on the ECG: T waves become flat or inverted, the ST segment may be depressed, U waves appear after the T wave, and the overall QT interval is prolonged. This combination—flat T waves or ST depression with prominent U waves and a prolonged QT—is classic for hypokalemia and reflects the heart’s delayed repolarization.

Why other patterns don’t fit hypokalemia: patterns with peaked T waves and ST elevation with a shortened QT point to hyperkalemia, not hypokalemia. A sine-wave pattern with a widened QRS indicates severe hyperkalemia. Pathologic Q waves with widespread ST elevation suggests a myocardial infarction, not electrolyte-related changes.

So the description of flat T waves or ST depression with U waves and prolonged QT best matches hypokalemia.