Electrolyte disorders and arrhythmogenesis.

Electrolyte disorders can alter cardiac ionic currents kinetics and depending on the changes can promote proarrhythmic or antiarrhythmic effects. The present report reviews the mechanisms, electrophysiolgical (EP), electrocardiographic (ECG), and clinical consequences of electrolyte disorders. Potassium (K⁺) is the most abundent intracellular cation and hypokalemia is the most commont electrolyte abnormality encountered in clinical practice. The most significant ECG manifestation of hypokalemia is a prominent U wave. Several cardiac and non cardiac drugs are known to suppress the HERG K⁺ channel and hence the I(K), and especially in the presence of hypokalemia, can result in prolonged action potential duration and QT interval, QTU alternans, early afterdepolarizations, and torsade de pointes ventricular tachyarrythmia (TdP VT). Hyperkalemia affects up to 8% of hospitalized patients mainly in the setting of compromised renal function. The ECG manifestation of hyperkalemia depends on serum K⁺ level. At 5.5-7.0 mmol/L K⁺, tall peaked, narrow-based T waves are seen. At > 10.0 mmol/L K⁺, sinus arrest, marked intraventricular conduction delay, ventricular techycardia, and ventricular fibrillation can develop. Isolated abnormalities of extracellular calcium (Ca⁺⁺) produce clinically significant EP effects only when they are extreme in either direction. Hypocalcemia, frequently seen in the setting of chronic renal insufficiency, results in prolonged ST segment and QT interval while hypercalcemia, usually seen with hyperparathyroidism, results in shortening of both intervals. Although magnesium is the second most abudent intracellular cation, the significance of magnesium disorders are controversial partly because of the frequent association of other electrolyte abnormalities. However, IV magnesium by blocking the L-type Ca(⁺⁺) current can successfully terminate TdP VT without affecting the prolonged QT interval. Finally, despite the frequency of sodium abnormalities, particularly hyponatremia, its EP effects are rarely clinically significant.