23-48: Hypokalemia

Maite A. Huis in ‘t Veld; Amal Mattu; R. Jason Thurman

ECG Findings

Flattened or inverted T waves
Prominent U waves that can merge with the T waves producing the appearance of a prolonged QT
ST-segment depression
Conduction disturbances

Pearls

Hypokalemia can produce varied ECG changes associated with the repolarization phase of the cardiac cycle.
Unlike hyperkalemia, in hypokalemia, there is no direct correlation with the potassium level and the severity of ECG changes. However, more ECG changes may become apparent as the potassium level falls.
Suspect hypomagnesemia if the ECG does not normalize after potassium replacement.

FIGURE 23.49A

Hypokalemia. (ECG contributor: R. Jason Thurman, MD.)

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FIGURE 23.49B

This ECG demonstrates multiple findings consistent with hypokalemia: flattened T waves (blue arrowhead), U waves (black arrowhead), prolonged QT (QU) intervals (double arrow), and ST-segment depression (arrow). This patient’s potassium level was 1.9.