Electrolyte Disorders

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


ECG characteristics of hyperkalemia, high blood potassium:

  • P-waves are widened and of low amplitude due to slowing of conduction
  • QRS complex:
    • QRS widening
    • fusion of QRS-T
    • loss of the ST segment
  • Tall tented T waves

The initial part of the QRS complex is often spared as purkinje fibers are less sensitive to hyperkalemia. These changes can also occur in acidosis (via the same mechanism) and during Class IC anti-arrhythmic intoxication.

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


Hypokalemia, low blood potassium, results in:

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


Hypercalcemia, high blood calcium, speeds 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, low blood calcium:

  • 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