Key result
Combined hypopotassemia and hypocalcemia prolongs S-T and Q-T intervals, merging T and U waves.
Observational
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.
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Surawicz et al. (1953) conducted an observational in Hypopotassemia with and without hypocalcemia. Hypopotassemia with and without hypocalcemia vs. Normal subjects was evaluated on Electrocardiographic pattern (Q-U interval, S-T, Q-T). Hypopotassemia typically causes S-T depression and T wave inversion, whereas combined hypopotassemia and hypocalcemia prolongs S-T and Q-T intervals, causing merging between T and U waves.