ECG changes in Hypokalemia:

QRS Complex: Begins to widen at a serum potassium level of about 3.0 mEq/L.
ST Segments: May become depressed by 1 mm or more.
T Waves: Begin to flatten at a serum potassium level of about 3.0 mEq/L and continue to become smaller as the U waves increase in size. The T waves may either merge with the U waves or become inverted.
U Waves: Begin to increase in size, becoming as tall as the T waves at a serum potassium level of about 3.0 mEq/L and, at about 2 mEq/L, becoming taller than the T waves. The U waves reach "giant" size and fuse with the T waves at 1 mEq/L.
QT Intervals: May appear to be prolonged when the U waves become prominent and fuse with the T waves but actually remain normal.
Associated Arrythmias: Ventricular arrhythmias, including the torsade de pointes form of ventricular tachycardia. May occur in hypokalemia in the presence of digitalis.

© Dr. Satish’06