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). The presence of a prolonged QT interval places the patient at risk for Torsade de Pointes.
Hypokalemia
![hypokalemia@2x](https://www.ecgstampede.com/wp-content/uploads/2022/11/hypokalemia@2x.png)
Examples
![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2022/11/13-Hypokalemia.jpg)
Hypokalemia
Hypokalemia tends to prolong the QT interval by way of delaying repolarization, creating a broad-based T wave, U waves, and T-U fusions.![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2022/12/24-HypoK-Ectopy_1-1-scaled.jpg)
Hypokalemia
Frequent ventricular ectopy places this patient at risk for torsade de pointes.![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2022/11/27-LongQT-scaled.jpg)
Hypokalemia
There is frequent ventricular ectopy placing this patient at risk for torsade de pointes.![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2022/11/64-HypoK.jpg)
Hypokalemia
While there is quite a bit of baseline artifact, a prolonged QT interval with broad-based T waves is evident. This patient was severely hypokalemic and intermittently went into polymorphic ventricular tachycardia. Overdrive pacing via a temporary transvenous pacer was initiated to avoid further episodes of polymorphic ventricular tachycardia.![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2023/01/162-HypoK-scaled.jpg)
Hypokalemia
This patient had a potassium of 1.5 mEq/L and presented with frequent falls. Notice the prolonged repolarization phase. The downward deflected T wave in the anterior precordial leads fuse with the U wave and create a wavy pattern characteristic of hypokalemia.![ECG Showing Hypokalemia](https://www.ecgstampede.com/wp-content/uploads/2023/05/173-HypoK-scaled.jpg)
Hypokalemia
This patient presented with global weakness and was diagnosed with hypokalemic periodic paralysis. The potassium level was 1.9 mEq/L. Note the prolonged QT interval and the U waves.References
- Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. Electrocardiographic manifestations: Electrolyte abnormalities. Journal of Emergency Medicine. 2004;27(2):153-160.
- Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. Journal of the American College of Cardiology. 2018;72(14):e91-e220.