Normal serum magnesium levels are generally considered to be 0.8 – 1.0 mmol/L. Hypomagnesaemia, defined as a level < 0.8 mmol/L, is associated with QT interval prolongation and an increased risk of ventricular arrhythmias.

ECG changes in isolated hypomagnesaemia

Patients with hypomagnesaemia often have concurrent hypokalaemia and/or hypocalcaemia and associated ECG features of these conditions.

Most literature on the ECG in hypomagnesaemia has not excluded patients with these other electrolyte disturbances, making exact changes difficult to ascertain. The only identifiable study examining patients with isolated hypomagnesaemia found no significant differences in QRS duration or ST segments compared to baseline ECGs.

Clinical relevance
  • 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
  • A rapid IV bolus of magnesium 2g is a standard emergency treatment for torsades de pointes
  • Further information regarding the causes and other clinical manifestations of hypomagnesaemia can be found here

ECG examples
Example 1
ECG Hypomagnesemia prolonged QT
Hypomagnesaemia with QTC prolonged at 510ms

The following ECGs were taken from a 76-year-old man presenting with palpitations. He was found to have a serum Magnesium level of 0.28 mmol/L.

Example 2a
ECG Hypomagnesemia nonsustained ventricular tachycardia 1
  • There are runs of nonsustained ventricular tachycardia (NSVT), as well as ventricular ectopics
  • QTC during normal rhythm is 465ms
Example 2b
ECG Hypomagnesemia nonsustained ventricular tachycardia 2
  • Repeat ECG 30 minutes later, when the patient entered conscious sustained VT


Advanced Reading



LITFL Further Reading


MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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

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