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. doi: 10.1016/j.jemermed.2004.04.006. [DOI] [PubMed] [Google Scholar]
- 2.El-Sherif N, Turitto G. Electrolyte disorders and arrythmogenesis. Cardiol J. 2011;18(3):233–45. [PubMed] [Google Scholar]
- 3.Glancy DL, Wiklow FE, Rochon BJ. Electrocardiogram after 2 weeks of diarrhea. Proc (Bayl Univ Med Cent) 2010;23(2):173–4. doi: 10.1080/08998280.2010.11928613. [DOI] [PMC free article] [PubMed] [Google Scholar]