Hypomagnesaemia Overview

• Normal serum magnesium = 0.8 – 1.0 mmol/L.
• Hypomagnesaemia = <0.8 mmol/L

ECG changes in Hypomagnesaemia

• 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.

Example ECG

Hypomagnesaemia causing long QTc (510ms)

Related Topics

• QT interval
• Hyperkalemia
• Hypokalemia
• Hypercalcemia
• Hypocalcemia

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest

Advanced Reading

• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
• Wagner GS. Marriott’s Practical Electrocardiography 12e
• Chan TC. ECG in Emergency Medicine and Acute Care
• Rawshani A. Clinical ECG Interpretation
• Mattu A. ECG’s for the Emergency Physician
• Hampton JR. The ECG In Practice, 6e

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John Larkin

Emergency Medicine Specialist MBChB FRCEM FACEM. Medical Education, Cardiology and Web Based Resources | @jjlarkin78 | LinkedIn |