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The earliest electrocardiogram (ECG) change associated with hypokalemia is a decrease in the T-wave amplitude.1 As potassium levels decline further, ST-segment depression and T-wave inversions are seen, while the PR interval can be prolonged along with an increase in the amplitude of the P wave.1 The U wave is described as a positive deflection after the T wave, often best seen in the mid-precordial leads (eg, V2 and V3). When the U wave exceeds the T-wave amplitude, the serum potassium level is < 3 mEq/L.2 In severe hypokalemia, T- and U-wave fusion with giant U waves masking the smaller preceding T waves becomes apparent on the ECG.1,2 A pseudo-prolonged QT interval may be seen, which is actually the QU interval with an absent T wave.1 Severe hypokalemia can also cause a variety of tachyarrhythmias, including ventricular tachycardia/fibrillation and rarely atrioventricular block.3 Treatment of hypokalemia involves parenteral and oral potassium supplementation, as well as identification and treatment of the underlying cause.1
Figure 1 12-lead ECG from a 21-year-old man with syncope, generalized weakness, and severe hypokalemia (serum potassium 1.6 mEq/L).
Demonstrates prolonged QT interval (649 ms), ST-segment depression, prominent U waves and slurring of the T waves into the U waves (most prominent in lead II).
Figure 2 12-lead ECG from same patient following oral and intravenous potassium replacement (serum potassium 2.5 mEq/L).
Demonstrates improvement in ST-segment depression, less prominent U waves and decreased QT prolongation (590 ms).

References

1.
Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. Electrocardiographic manifestations: electrolyte abnormalities. J Emerg Med. 2004 27(2):153-60.
2.
El-Sherif N, Turitto G. Electrolyte disorders and arrythmogenesis. Cardiol J. 2011 18(3):233-45.
3.
Glancy DL, Wiklow FE, Rochon BJ. Electrocardiogram after 2 weeks of diarrhea. Proc (Bayl Univ Med Cent). 2010 23(2):173-4.

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Published In

cover image The Permanente Journal
The Permanente Journal
Volume 16Number 2June 1, 2012
Pages: 57
PubMed: 22745618

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Joel T Levis, MD, PhD, FACEP, FAAEM

Notes

Joel T Levis, MD, PhD, FACEP, FAAEM, is a Senior Emergency Medicine Physician at the Santa Clara Medical Center, and Clinical Instructor of Emergency Medicine (Surgery) at Stanford University. He is the Medical Director for the Foothill College Paramedic Program in Los Altos, CA. E-mail: [email protected].

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