Metabolic and drug effects
Hyperkalaemia
Tall tented T waves, a flattening P wave and a widening QRS on its way to a sine wave.
58 bpmSinus, P waves disappearing
What you see
- Peaked, narrow-based, symmetrical T waves — the earliest change.
- P wave amplitude falls and the PR lengthens; eventually the P disappears.
- Progressive QRS widening with no bundle branch block morphology.
- Sine wave appearance immediately before ventricular fibrillation or asystole.
Why it looks like that
A raised extracellular potassium raises the resting membrane potential, which inactivates sodium channels and slows conduction — hence the wide QRS and vanishing P wave. Repolarisation is simultaneously accelerated, which peaks the T wave.
What to do
- IV calcium gluconate or chloride immediately for any ECG change — it stabilises the myocardium within minutes and buys time.
- Insulin with dextrose, and salbutamol, to shift potassium intracellularly.
- Remove potassium: dialysis, or a potassium binder in the non-acute setting.
- Stop ACE inhibitors, ARBs, spironolactone, trimethoprim and NSAIDs.
The trap
The ECG changes correlate poorly with the serum level — some patients arrest at 6.5 mmol/l and others look well at 9. Treat the ECG, not the number, and never wait for a repeat sample before giving calcium.
tented T wavescalcium gluconatesine waveinsulin dextrose