Hypocalcemia

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Hypokalemia, hypomagnesemia, and hypocalcemia can all cause a prolongation of the QT interval. While hypokalemia and hypomagnesemia both delay the repolarization phase (phase 3) of the of the cardiac action potential (creating wide-based T waves, U waves, or a fusion of both), hypocalcemia prolongs the QT interval by way of extending the plateau phase (phase 2) of the cardiac action potential (lengthening the ST segment but with a normal T wave).

Examples

ECG Showing Hypocalcemia

Hypocalcemia

QT prolongation by way of lengthened ST segment is specific for hypocalcemia (as opposed to broadening of the T wave or T-U fusion). The peaked T waves also suggest hyperkalemia. This is a classic ECG for patients with end-stage renal disease.
ECG Showing Hypocalcemia

Hypocalcemia

This patient presented with fatigue and was found to have newly discovered renal failure. The calcium was 5.6 mg/dL.

References

  1. Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. Electrocardiographic manifestations: Electrolyte abnormalities. Journal of Emergency Medicine. 2004;27(2):153-160.