Disorders of Calcium and Phosphate Metabolism Practice Test 2026 – The Complete Guide to Exam Mastery!

Calcium shapes the plateau phase of the ventricular action potential, which directly affects how long the ventricles stay depolarized before finishing repolarization. In hypocalcemia, there is less calcium available to drive that plateau, so repolarization is delayed and the ST segment lengthens. This lengthening of the ST segment spreads into a longer QT interval on the ECG. That’s why hypocalcemia commonly presents with a prolonged QT interval.

Hypercalcemia does the opposite and shortens the QT interval, while ST elevation or inverted T waves point to other conditions such as pericarditis, ischemia, or infarction rather than calcium balance. The prolonged QT in hypocalcemia also raises the risk of torsades de pointes, a potentially dangerous arrhythmia.