Clinical Notes : Cardiology

112. ECG - Hyperkalemia

ECG - Hyperkalemia


  • Hyperkalaemia is defined as a potassium level > 5,0 - 5.5 mEq/L in adults

    • the range in infants and children is age-dependent

  • Moderate hyperkalaemia is a serum potassium > 6.0 mEq/L

  • Severe hyperkalaemia is a serum potassium > 7.0 mE/L


  • Potassium is vital for regulating the normal electrical activity of the heart.

  • Increased extracellular potassium reduces myocardial excitability, with depression of both pacemaking and conducting tissues.

  • Progressively worsening hyperkalaemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system, resulting in bradycardia and conduction blocks and ultimately cardiac arrest



Serum potassium > 5.5 mEq/L


is associated with repolarization abnormalities:

  • Peaked T waves (usually the earliest sign of hyperkalaemia)


Peaked T waves

Serum potassium > 6.5 mEq/L


is associated with progressive paralysis of the atria:

  • P wave widens and flattens

  • PR segment lengthens

  • P waves eventually disappear


Prolonged PR segment

Loss of P waves


Serum potassium > 7.0  mEq/L


is associated with conduction abnormalities and bradycardia:

  • Prolonged QRS interval with bizarre QRS morphology

  • High-grade AV block with slow junctional and ventricular escape rhythms

  • Any kind of conduction block (bundle branch blocks, fascicular blocks)

  • Sinus bradycardia or slow AF

  • Development of a sine wave appearance (a pre-terminal rhythm)


Sine wave

Serum potassium level of > 9.0 mEq/L


causes cardiac arrest due to:

  • Asystole

  • Ventricular fibrillation

  • PEA with bizarre, wide complex rhythm


This ECG displays many of the features of hyperkalaemia:

  • Prolonged PR interval.

  • Broad, bizarre QRS complexes — these merge with both the preceding P wave and subsequent T wave.

  • Peaked T waves.

This patient had a serum K+ of 9.2. 


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