Which statement about electrolyte disturbances and QT interval is true?

• A. Electrolyte disturbances can cause prolonged QT
• B. QT prolongation is unaffected by electrolyte levels
• C. Potassium has no effect on QT interval
• D. Calcium does not influence QT

Answer: (A)

The QT interval reflects how long ventricular repolarization takes, so anything that alters the ions guiding cardiac cells can change its duration. Electrolyte balance directly influences this process: low potassium (hypokalemia), low magnesium (hypomagnesemia), and low calcium (hypocalcemia) slow repolarization and lengthen the QT interval. In contrast, high calcium (hypercalcemia) tends to shorten the QT interval. Because electrolyte abnormalities can delay repolarization and extend the QT, the statement that electrolyte disturbances can cause prolonged QT is true.

Not true aspects to note: electrolyte levels do affect QT, so saying QT prolongation is unaffected by electrolytes is incorrect; potassium does influence QT; calcium does influence QT (hypocalcemia prolongs QT, hypercalcemia shortens QT).