Hypokalemia electrocardiogram

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Assistant Editor(s)-In-Chief: Jack Khouri

Overview

The most notable EKG findings in hypokalemia are due to the delayed ventricular repolarization, manifesting as (QT-U) with prominent U waves. It is commonly seen at potassium levels <3 meq/L (90% of patients with potassium levels <2.7 meq/L have abnormal ECG findings). However, these changes are rapidly reversible with potassium repletion

ECG changes

1. ST segment depression, decreased T wave amplitude, prominent U waves
   • seen in 78% of patients with a K < 2.7 meq
   • seen in 35% of patients with a K > 2.7 and < 3.0
   • seen in 10% of patients with a K > 3.0 and < 3.5
   • U waves are also prominent in bradycardia and LVH
2. Prolongation of the QRS duration
   • uncommon except in severe hyperkalemia
3. Increase in the amplitude and duration of the P-wave
4. Cardiac arrhythmias and AV block
5. Contrary to popular belief there is not prolongation of the QTc, this is artifactually prolonged due to the U wave. In some cases there is fusion of the T and the U wave making interpretation impossible.

ECG Imaging

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  Long QT interval, ST segment depression, low T waves amplitude and TU wave fusion in a hypokalemic patient.

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  Consecutive ECGs of a patient with hypokalemia. ECG1

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  Consecutive ECGs of a patient with hypokalemia. ECG2

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  Consecutive ECGs of a patient with hypokalemia. After correction of potassium levels.

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  Hypokalemia with LVH. Image courtesy of Dr Jose Ganseman

Treatment

The changes of hypokalemia are rapidly reversible with potassium repletion.

References

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