What is the classic ECG finding in hypokalemia and the initial treatment approach?

• A. Peaked T waves with prominent U waves; treat with potassium repletion and magnesium
• B. Flattened/inverted T waves with prominent U waves; treat with potassium repletion, limiting IV rate to ≤10 mEq/hr and correcting magnesium if needed
• C. Prolonged QT interval; give calcium
• D. ST elevations; administer diuretics

Answer: (B)

In hypokalemia, the classic ECG finding is a combination of flattened or inverted T waves with a prominent U wave, often with ST segment flattening or depression and a tendency toward a longer QT interval. The main reason this pattern matters is that it directly points to low potassium as the electrolyte disturbance needing correction. The initial treatment is potassium repletion, started promptly and tailored to severity and symptoms. Potassium can be given orally for mild cases or when the patient can tolerate it, and intravenously for more severe cases or when oral administration isn’t possible. When giving IV potassium, the rate is typically limited to about 10 mEq per hour and the patient is closely monitored with ECG to avoid dangerous arrhythmias. It’s also important to check and correct magnesium if needed, because low magnesium impairs potassium repletion and can hinder correction of the hypokalemia. So the combination of the characteristic U waves with flattened T waves guides both recognition and the need for careful potassium replacement, with magnesium correction as a common accompanying step. The other options describe patterns and treatments that don’t fit hypokalemia (peaked T waves suggest hyperkalemia; prolonged QT with calcium suggests hypocalcemia; ST elevations with diuretics isn’t a typical hypokalemia scenario).