Hypocalcaemia QT Prolongation TdP Risk — FRCA Final MCQ

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ModerateGeneral AnaesthesiaHypocalcaemia QT Prolongation TdP RiskFRCA Final

A 55-year-old woman (ASA III) with chronic kidney disease and secondary hyperparathyroidism undergoes parathyroidectomy. Post-operatively her ionised calcium drops to 0.85 mmol/L (normal 1.1-1.3) and she develops QTc prolongation to 520 ms. The most important ECG monitoring concern is:

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Correct answer: E — Torsades de pointes

Severe hypocalcaemia (ionised Ca <0.9 mmol/L) causes significant QT prolongation by prolonging the ST segment. A QTc >500 ms places the patient at high risk of torsades de pointes (TdP), a polymorphic ventricular tachycardia that can degenerate into VF. Treatment of the hypocalcaemia: IV calcium gluconate 10 mL of 10% over 10 minutes (may need repeated doses or infusion), correct hypomagnesaemia if present (Mg is a cofactor for PTH secretion and action), and start alfacalcidol. Continuous ECG monitoring is mandatory until ionised calcium normalises.

Reference: RCOA – 2023 – Electrolyte physiology; Resuscitation Council UK – 2021 – Arrhythmia management