Hyperkalaemia
- Normal level of Potassium is vital for regulating the normal electrical activity of the heart.
- Increased extracellular potassium level 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.
Definitions
- Hyperkalaemia is defined as a potassium level > 5.5 mEq/L
- Moderate hyperkalaemia is a serum potassium > 6.0 mEq/L
- Severe hyperkalaemia is a serum potassium > 7.0 mE/L
Effects of hyperkalaemia on the ECG
Serum potassium > 5.5 mEq/L is associated with repolarization abnormalities:
- Peaked T waves (usually the earliest sign of hyperkalaemia)
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
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)
Serum potassium level of > 9.0 mEq/L causes cardiac arrest due to:
- Asystole
- Ventricular fibrillation
- PEA with bizarre, wide complex rhythm
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