Cardiac Electrophysiology Practice Test 2026 - Free Cardiac Electrophysiology Practice Questions and Study Guide

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.