Hypocalcaemia

Hypocalcaemia causing a long QTc (510ms)

Definitions

• 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.

Causes

• 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)

Symptoms

• Neuromuscular excitability
• Carpopedal spasm
• Tetany
• Chvostek’s sign
• Trousseau’s sign
• Seizures

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

• Hypercalcaemia
• Measurement of the QT interval

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits

• Words – Ed Burns
• Pictures – Ed Burns
• Web Editing – Ed Burns

References

• 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.