Which electrolyte abnormality is most commonly associated with muscle weakness and arrhythmias?

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

Answer: (D)

Potassium sets the resting electrical potential of muscle and heart cells, so changing its level directly changes how easily these cells fire. When there’s too much potassium outside the cells (hyperkalemia), the resting membrane potential becomes less negative. That partial depolarization inactivates some sodium channels, which slows down or blocks the initiation and propagation of action potentials. In skeletal muscle, this makes muscles weak or even paralyzed because they can’t contract reliably. In the heart, slowed conduction and abnormal repolarization predispose to dangerous rhythm disturbances, i.e., arrhythmias. Because these effects strikingly link high potassium to both muscle weakness and arrhythmias, hyperkalemia best fits the question.