Hypocalcaemia causing a long QTc (510ms)


  • Normal serum corrected calcium = 2.2 – 2.6 mmol/L.
  • Mild-moderate hypocalcaemia =  1.9 – 2.2 mmol/L.
  • Severe hypocalcaemia = < 1.9 mmol/L.


  • Hypoparathyroidism
  • Vitamin D deficiency
  • Acute pancreatitis
  • Hyperphosphataemia
  • Hypomagnesaemia
  • Diuretics (frusemide)
  • Pseudohypoparathyroidism
  • Congenital disorders (e.g. DiGeorge syndrome)
  • Critical illness (e.g. sepsis)
  • Factitious (e.g. EDTA blood tube contamination)


ECG changes

  • Hypocalcaemia causes QTc prolongation primarily by prolonging the ST segment.
  • The T wave is typically left unchanged.
  • Dysrhythmias are uncommon, although atrial fibrillation has been reported.
  • Torsades de pointes may occur, but is much less common than with hypokalaemia or hypomagnesaemia.

More Examples

Example 1 – QTc 500ms in a patient with hypoparathyroidism (post thyroidectomy) and serum corrected calcium of 1.40 mmol/L

Reproduced from Nijjer et al. (2010)

Example 2 – QT prolongation in a patient with DiGeorge’s syndrome and serum calcium of 1.32 mmol/L 

Reproduced from Kar et al. (2005)

Related Topics

Further Reading


  • Chan TC, Brady WJ, Harrigan RA, Ornato JP and Rosen PR. ECG in Emergency Medicine and Acute Care. Elsevier 2005
  • Kar PS, Ogoe B, Poole R, Meeking D. Di-George syndrome presenting with hypocalcaemia in adulthood: two case reports and a review. J Clin Pathol. 2005 Jun;58(6):655-7.
  • Kumar P, Clark M. Kumar & Clark’s Clinical Medicine (7th edition). London: Elsevier (2009).
  • Nijjer S, Ghosh AK, Dubrey SW. Hypocalcaemia, long QT interval and atrial arrhythmias. BMJ Case Reports 2010; doi:10.1136/bcr.08.2009.2216 [full text].
  • Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
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