Hyperkalaemia and hypokalaemia on the 12-lead

Both potassium disorders as progressions you can step through. Hyperkalaemia from peaked T waves at K⁺ 6, through a long PR and a wide QRS, to the sine wave and ventricular fibrillation. Hypokalaemia from a flatter T and a small U at K⁺ 3.0, through ST depression and a U taller than the T, to torsades de pointes. Each form has its own short article, and tapping a lead shows its measurements beside the normal range.