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).
Hypocalcemia
![prolonged-qt@2x](https://www.ecgstampede.com/wp-content/uploads/2022/11/prolonged-qt@2x.png)
Examples
![ECG Showing Hypocalcemia](https://www.ecgstampede.com/wp-content/uploads/2022/11/143-hypoCa-1-scaled.jpg)
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.References
- Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. Electrocardiographic manifestations: Electrolyte abnormalities. Journal of Emergency Medicine. 2004;27(2):153-160.