The electrocardiographic pattern of hypopotassemia with and without hypocalcemia.

Detailed analysis of the electrocardiogram in patients with hypopotassemia without hypocalcemia showed that the Q-U interval and its components (Q-oT, Q-aT, Q-T, and Q-aU) have essentially the same duration as in normal subjects for the same heart rate and sex. The typical hypopotassemia pattern is characterized by progressive depression of S-T, lowering and inversion of T and increase of U in left precordial leads. In hypopotassemia with hypocalcemia S-T and Q-T, but not Q-U, are prolonged, causing an increased degree of merging between T and U. Three methods of differentiation between completely merged T and U waves and true T waves of long Q-T duration are given.