Electrolyte Disorders

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Author(s) J.S.S.G. de Jong
Moderator T.T. Keller
some notes about authorship


Hypercalcemia results in a faster repolarization. Characteristics of hypercalcemia:

  • mild: broad based tall peaking T waves
  • severe: extremely wide QRS, low R wave, disappearance of p waves, tall peaking T waves.


ECG-characteristics of hypocalcemia:

  • narrowing of the QRS complex
  • reduced PR interval
  • T wave flattening and inversion
  • prolongation of the QT-interval
  • prominent U-wave
  • prolonged ST and ST-depression


Extreme hyperkalemia. No p-waves, wide QRS, tall peaking T waves.
Same patient after partial correction of the potassium level. Still no p-waves visible, wide QRS, tall peaking T waves.

ECG characteristics of hyperkalemia:

  • Tall peaked T waves
  • Flattening p-waves. In extreme hyperkalemia p-waves may disappear altogether.
  • Prolonged depolarization leading to QRS widening (nonspecific intraventricular conduction defect) sometimes > 0.20 seconds

At concentrations > 7.5 mmol/L atrial and ventricular fibrillation can occur.


Consecutive ECGs of a patient with hypokalemia. ECG1
Consecutive ECGs of a patient with hypokalemia. ECG2
Consecutive ECGs of a patient with hypokalemia. After correction of potassium levels.

Hypokalemia is a low blood potassium level. This results in:

  • ST depression and flattening of the T wave
  • Negative T waves
  • A U-wave may be visible