Which electrolyte abnormality is most often associated with tall peaked T waves on ECG?

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

Answer: (B)

Elevated potassium levels alter how the ventricles repolarize, and tall, peaked T waves are a classic early ECG sign of hyperkalemia. As extracellular potassium rises, ventricular myocytes repolarize more rapidly, which makes the T wave taller and narrower. This change is often one of the first clues on the ECG that potassium is too high. If potassium continues to climb, other changes follow—PR interval may lengthen, P waves may flatten or disappear, QRS complexes can widen, and a sine-wave pattern can develop as the risk of life-threatening arrhythmias increases.

In contrast, very low potassium tends to flatten T waves and produce prominent U waves; hyponatremia has more systemic effects and doesn’t produce this characteristic tall T-wave pattern; hypercalcemia tends to shorten the QT interval rather than tall T waves.