ECG changes in hyperkalaemia

Last edited 02/2018 and last reviewed 10/2022

Hyperkalaemia causes a rapid reduction in resting membrane potential leading to increased cardiac depolarization, and muscle excitability which in turn causes EG changes (1).

ECG changes are usually progressive and may include:

  • tall, peaked (tented) T waves [T wave larger than R wave in more than 1 lead]
  • first degree heart block (prolonged PR interval) [>0.2 s];
  • flattened or absent P waves
  • ST-segment depression
  • S and T wave merging (sine wave pattern)
  • widened QRS [>0.12 s]
  • arrythmias including bradycardia, ventricular tachycardia or fibrillation
  • cardiac arrest (pulseless electrical activity [PEA], ventricular fibrillation/pulseless ventricular tachycardia [VF/VT], asystole) (2)

ECG changes with hyperkalaemia do not consistently follow a stepwise, dose-dependent pattern.

  • risk of arrhythmias increase with potassium values > 6.5 mmol/L and even small elevations in potassium above this concentration can lead to rapid progression from peaked T waves to ventricular fibrillation or asystole
  • the longer a patient has high potassium concentrations, the greater the risk of sudden deterioration (1)

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  • ECG finding are neither specific nor sensitive for detecting hyperkalaemia (3)