ECG Diagnosis: Hypokalemia


Joel T Levis, MD, PhD, FACEP, FAAEM

Spring 2012 - Volume 16 Number 2

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

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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