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Lesson 20 of 21 · Advanced

Electrolyte Abnormalities

Potassium and calcium change repolarization in predictable ways. Hyperkalemia is the one that kills: learn its progression cold.

01Hyperkalemia progression

Hyperkalemia progression
NormalK⁺ 3.5–5.0Peaked TK⁺ 5.5–6.5Wide QRS, flat PK⁺ 6.5–8.0Sine waveK⁺ > 8.0 → VF
V3
Peaked T waves.
II
Flattened P, long PR, wide QRS.
II
Sine wave: pre-arrest. Give calcium now.

02Hypokalemia

II
Flat T waves, ST depression, prominent U waves.

03Calcium

  • Hypocalcemia: long QT (prolonged ST segment)
  • Hypercalcemia: short QT
II
Prolonged QT: hypocalcemia, hypokalemia, hypomagnesemia, drugs.

Clinical pearl. In a dialysis patient with bradycardia and a wide QRS, give calcium before you get the potassium level back.

Key takeaways

  • HyperK: peaked T → wide QRS → sine wave
  • HypoK: U waves
  • Ca²⁺: low = long QT, high = short QT