- Normal serum magnesium = 0.8 – 1.0 mmol/L.
- Hypomagnesaemia = <0.8 mmol/L
- The primary ECG abnormality seen with hypomagnesaemia is a prolonged QTc.
- Atrial and ventricular ectopy, atrial tachyarrhythmias and torsades de pointes are seen in the context of hypomagnesaemia, although whether this is a specific effect of low serum magnesium or due to concurrent hypokalaemia is uncertain.
- Nevertheless, correction of serum magnesium to >1.0 mmol/L (with concurrent correction of serum potassium to >4.0 mmol/L) is often effective in suppressing ectopy and supraventricular tachyarrhythmias, while a rapid IV bolus of magnesium 2g is a standard emergency treatment for torsades de pointes.
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