Hypokalemia
Also calledLow potassium · Low K · Decreased K+ · Reduced serum potassium · K+ depletion
Definition
A low serum potassium level that prolongs ventricular repolarization (the QT interval). The earliest change is a fall in T-wave amplitude; as potassium falls further, ST-segment depression, T-wave inversion and increasingly prominent U waves appear, sometimes with PR prolongation and taller P waves. As the T wave shrinks and the U wave grows the two can fuse, giving a pseudo-prolonged QT that is actually a QU interval; a U wave taller than the T wave usually means a potassium below about 2.7 to 3 mmol/L.
Clinical noteSevere hypokalemia predisposes to torsades de pointes and other ventricular arrhythmias, including ventricular tachycardia and fibrillation.
Sources
- Levis JT. ECG diagnosis: hypokalemia. Perm J. 2012;16(2):57. doi.org/10.7812/tpp/12-015
- Gentry BC, Viera AJ. Photo quiz. A subtle ECG. Am Fam Physician. 1999;59(9):2581-2582. www.aafp.org/pubs/afp/issues/1999/0501/p2581.html
- Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation. 2010;121(8):1047-1060. doi.org/10.1161/CIRCULATIONAHA.109.192704
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.