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Hyperkalaemia

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Hyperkalaemia produces a progressive sequence of ECG changes as serum potassium rises: peaked T waves, PR prolongation, P-wave flattening, QRS widening and finally a sine-wave pattern. The ECG correlates imperfectly with the potassium level, and severe changes can precede cardiac arrest.

ECG criteria

  • Tall, narrow, symmetrical peaked T waves (the earliest sign, best seen in the precordial leads).
  • Prolonged PR interval, then flattening and loss of P waves.
  • Widening of the QRS complex, with merging of QRS and T waves.
  • Sine-wave pattern as a pre-terminal sign, followed by ventricular fibrillation, asystole or pulseless electrical activity.
  • Bradycardia, AV block, ST elevation mimicking infarction (pseudo-infarct) and bundle branch block patterns may occur.

Mechanism

Extracellular potassium excess raises the resting membrane potential toward threshold, first accelerating repolarisation (peaked T), then inactivating sodium channels, which slows conduction (wide QRS, PR prolongation, loss of P waves). Eventually conduction fails, giving ventricular arrhythmia or asystole.

Common causes

  • Acute and chronic kidney disease (reduced renal excretion).
  • Drugs: ACE inhibitors, angiotensin receptor blockers, potassium-sparing diuretics, potassium supplements, trimethoprim.
  • Cell breakdown or shift: rhabdomyolysis, tumour lysis, haemolysis, tissue injury, acidosis, insulin deficiency.
  • Adrenal insufficiency; spurious hyperkalaemia from haemolysed samples or marked leucocytosis or thrombocytosis.

Management principles

Treatment follows the severity and ECG changes: protect the myocardium, shift potassium into cells, remove excess potassium and treat the cause, according to the local hyperkalaemia protocol. ECG changes indicate an emergency; no doses are given here and local guidelines apply.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • The ECG can be normal in significant hyperkalaemia, and ECG changes correlate poorly with the measured level; treat the patient and the ECG, not the number alone.
  • Peaked T waves are not specific: they also occur in early anterior myocardial infarction, left ventricular hypertrophy and normal variants; hyperacute T waves in infarction are broader-based.
  • Wide QRS with a sine-wave pattern can be mistaken for ventricular tachycardia, and pseudohyperkalaemia from a haemolysed sample can mislead.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
  2. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)
  3. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)

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