Severe hyperkalemia affects conduction by causing what change in cell resting state?

• A. Hyperpolarization
• B. Depolarization
• C. No change
• D. Hyperexcitability

Answer: (B)

Severe hyperkalemia depolarizes the resting membrane potential. When extracellular potassium rises, the potassium equilibrium potential becomes less negative. Since the resting state of cardiac cells is largely governed by the K+ equilibrium potential, the cell membrane potential moves toward zero (less negative). This depolarization reduces the availability of voltage-gated sodium channels, which slows the upstroke of the action potential and slows conduction through the atrioventricular node, His-Purkinje system, and ventricles. Clinically, this manifests as slower conduction and characteristic ECG changes as potassium levels climb higher.