ECG diagnosis: The effect of ionized serum calcium levels on electrocardiogram.

High and low levels of ionized serum calcium concentration can produce characteristic changes on the electrocardiogram. These changes are almost entirely limited to the duration of the ST segment, with no change in the QRS complexes or T waves. High ionized serum calcium shortens the ST segment, and low ionized serum calcium prolongs the ST segment. Two common clinical scenarios are presented.