Clinical Notes : Cardiology
112. ECG - Hyperkalemia

ECG - Hyperkalemia
Definitions
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Hyperkalaemia is defined as a potassium level > 5,0 - 5.5 mEq/L in adults
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the range in infants and children is age-dependent
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Moderate hyperkalaemia is a serum potassium > 6.0 mEq/L
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Severe hyperkalaemia is a serum potassium > 7.0 mE/L
Background
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Potassium is vital for regulating the normal electrical activity of the heart.
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Increased extracellular potassium reduces myocardial excitability, with depression of both pacemaking and conducting tissues.
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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:
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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
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PR segment lengthens
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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
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High-grade AV block with slow junctional and ventricular escape rhythms
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Any kind of conduction block (bundle branch blocks, fascicular blocks)
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Sinus bradycardia or slow AF
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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
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Ventricular fibrillation
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PEA with bizarre, wide complex rhythm

This ECG displays many of the features of hyperkalaemia:
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Prolonged PR interval.
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Broad, bizarre QRS complexes — these merge with both the preceding P wave and subsequent T wave.
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Peaked T waves.
This patient had a serum K+ of 9.2.

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