Hyperkalemia Vs Hypokalemia - ECG Changes

Potassium (K⁺) is the dominant intracellular cation, with approximately 98% residing inside cells and only 2% in the extracellular fluid. This steep concentration gradient - maintained by the Na⁺/K⁺-ATPase pump - is the primary determinant of the resting membrane potential (RMP) of excitable cells, including cardiac myocytes and skeletal muscle fibers. The normal RMP of a cardiac ventricular cell is approximately −90 mV, generated largely by potassium leak channels that allow K⁺ to flow down its concentration gradient from intracellular to extracellular space. When extracellular K⁺ rises (hyperkalemia), the gradient decreases, the RMP becomes less negative (partially depolarized), and the cell becomes hyperexcitable initially but progressively inexcitable as sodium channels inactivate. When extracellular K⁺ falls (hypokalemia), the gradient steepens, the RMP becomes more negative (hyperpolarized), making the cell harder to depolarize - but paradoxically more prone to ectopic pacemaker activity and re-entrant circuits due to prolonged repolarization. This is why both extremes of potassium produce life-threatening dysrhythmias: they disrupt the precisely calibrated electrical cycling of the heart. Normal serum potassium: 3.5-5.0 mEq/L. Even small deviations (0.5-1.0 mEq/L) can produce clinically...