ECG changes in electrolyte disturbance (U waves-hypokalaemia, peaked T-hyperkalaemia)
Core concept
- Potassium sets the resting membrane potential; calcium sets the plateau (phase 2) duration
- -> K+ abnormalities change the T wave, QRS and P wave. Ca2+ abnormalities change the ST segment and QT interval, with a normal T wave.
- Hyperkalaemia - inc extracellular K+ -> less negative resting potential -> Na channel inactivation
- -> slowed conduction (wide QRS), and faster repolarisation (tall narrow T)
- Hypokalaemia - hyperpolarised, prolonged repolarisation -> ST depression, flat T, U wave
- Hypocalcaemia - prolonged phase 2 -> long ST segment -> long QT with a normal-width T wave
- Hypercalcaemia - short ST -> short QT
3 more sections, plus exam facts
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