Clinical Notes : Cardiology

112. ECG - Hyperkalemia

ECG - Hyperkalemia

Definitions​

Background

Serum Potassium > 5,5 mEq/L

​​Serum Potassium > 6,5 mEq/L

​Serum Potassium > 7,0 mEq/L

​Serum Potassium > 9,0 mEq/L

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- References -

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Definitions

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• 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

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Background

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• 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

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Serum potassium > 5.5 mEq/L

is associated with repolarization abnormalities:

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• 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:

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• 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:

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• 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)

Bradycardia

Sine wave

Serum potassium level of > 9.0 mEq/L

causes cardiac arrest due to:

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• 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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