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. The EKG changes of hypokalemia are commonly seen at potassium levels < 3 meq/Li. 90% of the patients with potassium levels <2.7 meq/L have abnormal ECG findings.
Electrocardiogram
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 U waves making interpretation impossible.
ECG Examples
Shown below is an example of hypokalemia with long QT interval, ST segment depression, low T waves amplitude and TU wave fusion.
Shown below is an example of hypokalemia with Left Ventricular Hypertrophy.
The EKG below demonstrates characteristics of hypokalemia including: T wave inversions and U waves circled in red; flattening of ST segment and prolonged Q- U interval as circled in green.
The EKG changes of hypokalemia are rapidly reversible with potassium repletion.