Prolonged QTc Hypocalcaemia Hypomagnesaemia — ESENeph MCQ

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ModerateElectrolyte DisordersProlonged QTc Hypocalcaemia HypomagnesaemiaESENeph

A 65-year-old man with CKD G5D on haemodialysis is noted to have a prolonged QTc interval on ECG (510 ms). His calcium is 1.85 mmol/L and magnesium is 0.5 mmol/L. Potassium is 5.2 mmol/L. What electrolyte abnormality is most likely contributing to the prolonged QTc?

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Correct answer: D — Hypocalcaemia and hypomagnesaemia

Prolonged QTc is associated with hypocalcaemia (calcium prolongs phase 2 of the cardiac action potential) and hypomagnesaemia (magnesium stabilises ion channels). Both are common in haemodialysis patients. Hyperkalaemia characteristically shortens QT (and causes peaked T waves, wide QRS). Management involves IV calcium gluconate for both cardiac protection and calcium correction, plus IV magnesium replacement. Dialysate calcium and magnesium concentrations should be reviewed.

Reference: UK Resuscitation Council 2021; KDIGO 2017 – CKD-MBD