Which ECG change is characteristic of hyperkalemia?

• A. Prolonged QT interval
• B. Atrial fibrillation
• C. Tall peaked T waves
• D. ST segment depression

Answer: (C)

Elevated potassium levels alter how heart muscle cells conduct and repolarize, and the most recognizable ECG change is tall, peaked T waves. When extracellular potassium rises, the ventricles repolarize more quickly, which makes the T waves become tall and narrow. As potassium levels climb higher, conduction slows (due to partial inactivation of sodium channels), leading to PR interval prolongation and widening of the QRS complex. In severe hyperkalemia, a sine-wave pattern can appear and the risk of life-threatening arrhythmias increases.

So, the tall, peaked T waves are the classic and earliest ECG manifestation of hyperkalemia. Other changes like prolonged QT, atrial fibrillation, or ST-segment depression are not characteristic features of hyperkalemia and point to other processes.