The difficult diagnosis of hypokalemia.

The electrocardiographic diagnosis of uncomplicated hypokalemia rests on ST segment depression, a decrease in T-wave amplitude, prominent U waves and a U-wave to T-wave ratio of greater than 1. The diagnosis is more difficult in a patient receiving digitalis, but the upsloping ST segment of digitalis can be distinguished from that of hypokalemia. The changes of hypokalemia are most apparent in leads V2 and V3.