Which electrolyte disturbance is noted for causing characteristic changes in the ECG?

Hypokalemia is well-documented for its significant impact on the electrocardiogram (ECG). When potassium levels in the blood drop, various discernible changes can occur on an ECG tracing. Notably, these include the presence of U waves, which are small deflections that occur after the T wave, a prolonged QT interval, and in more severe cases, ST segment depression and T wave flattening or inversion. These changes occur due to the critical role potassium plays in maintaining normal cardiac myocyte depolarization and repolarization.

Each of the other electrolyte disturbances mentioned can affect heart function and might have ECG manifestations, but none exhibit the distinctive and well-defined patterns associated with hypokalemia. For instance, while hypocalcemia can lead to a prolonged QT interval and hypercalcemia can shorten it, these changes are not as specific or characteristic as those caused by hypokalemia. Similarly, hyponatremia has less direct impact on the cardiac rhythm and conduction system, making hypokalemia the most notable for its specific ECG changes.