Hypercalcemia commonly presents on ECG with which change?

• A. Prolonged QT interval
• B. Widened QRS complex
• C. Shortened QT interval
• D. ST segment depression

Answer: (C)

Elevated calcium speeds up ventricular repolarization, which shortens the QT interval on the ECG. The QT interval reflects the time from ventricular depolarization to repolarization; when serum calcium is high, the plateau phase of the ventricular action potential is shortened, leading to a shorter QT. In contrast, hypocalcemia prolongs the QT, wide QRS is more typical of severe hyperkalemia or conduction disturbances, and ST segment depression suggests ischemia. Therefore, the ECG change most characteristic of hypercalcemia is a shortened QT interval.