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.
Epidemiology and Demographics
The EKG changes of hypokalemia are commonly seen at potassium levels < 3 meq/Li. 90% of patients with potassium levels <2.7 meq/L have abnormal ECG findings.
Diagnosis
ECG changes
- 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
- Prolongation of the QRS duration
- uncommon except in severe hyperkalemia
- Increase in the amplitude and duration of the P-wave
- Cardiac arrhythmias and AV block
- 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 Examples
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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 EKG changes of hypokalemia are rapidly reversible with potassium repletion.