Which electrolyte disturbance is most commonly associated with prolonged QT interval on ECG?

Which electrolyte disturbance is most commonly associated with prolonged QT interval on ECG?

• A. Hyperkalemia
• B. Hypercalcemia
• C. Hypocalcemia
• D. Hypokalemia

Answer: (C)

The QT interval reflects how long the ventricles take to depolarize and then repolarize, so anything that slows ventricular repolarization will lengthen this interval. Calcium is a key player in the plateau phase of the ventricular action potential; when calcium levels are low, the plateau is prolonged, delaying repolarization and thus lengthening the QT interval. This makes hypocalcemia the electrolyte disturbance most classically linked to a prolonged QT. In contrast, higher calcium shortens the QT, and potassium disturbances tend to affect other aspects of repolarization (with hypokalemia sometimes prolonging QT but not as characteristically as hypocalcemia). So the most typical association with a prolonged QT is low calcium.

The QT interval reflects how long the ventricles take to depolarize and then repolarize, so anything that slows ventricular repolarization will lengthen this interval. Calcium is a key player in the plateau phase of the ventricular action potential; when calcium levels are low, the plateau is prolonged, delaying repolarization and thus lengthening the QT interval. This makes hypocalcemia the electrolyte disturbance most classically linked to a prolonged QT. In contrast, higher calcium shortens the QT, and potassium disturbances tend to affect other aspects of repolarization (with hypokalemia sometimes prolonging QT but not as characteristically as hypocalcemia). So the most typical association with a prolonged QT is low calcium.