Which of the following statements about the QT interval in hypocalcemia is correct?

• A. Shortened QT interval
• B. QT interval unchanged
• C. ST depression
• D. Prolonged QT interval

Answer: (D)

Hypocalcemia prolongs ventricular repolarization, which shows up as a longer QT interval on the ECG. Calcium helps the plateau phase of the cardiac action potential; when calcium is low, repolarization takes longer, extending the QT from the start of the QRS to the end of the T wave. That’s why the statement describing a prolonged QT interval is correct.

Smaller clues help solidify the concept: hypercalcemia shortens the QT interval, so a shortened QT would not fit hypocalcemia. QT interval being unchanged isn’t consistent with the slowed repolarization caused by low calcium, and ST depression isn’t the characteristic feature of hypocalcemia. Prolonged QT can raise the risk of dangerous arrhythmias like torsades de pointes, especially with other predisposing factors.