Causes and ECG Changes in Hypokalaemia

Hypokalaemia is caused by potassium-wasting diuretics, potassium-wasting diarrhoea and hypokalaemic periodic paralysis.

The hallmark of the effect of hypokalaemia on the ECG is the development of large U waves (positive deflection after the T wave). The normal U wave is produced by repolarisation of the His–Purkinje system.

ECG changes in uraemia

A prolonged QT interval is due to hypocalcaemia and tall T waves to hyperkalaemia and/or acidosis, which can be caused by uraemia. The main ECG change resulting from hypocalcaemia is a long QT interval due to prolongation of the ST segment.