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Potassium: ECG changes

Hypokalemia (see images 1 and 2)

Earliest change →ST-segment depression, T-wave flattening and inversion, PR interval prolongation along with increase in P-wave amplitude.

Later changes → U-wave (often in leads V2 and V3)

When Serum K < 2 meq/L → U and T waves fuse (giant U waves mask smaller preceding T wave)

Pseudo-prolonged QT interval → Actually QU interval in absence of T wave.

Severe hyperkalemia → Tachyarrhythmia (ventricular tachycardia and fibrillation)

→ Rare occasions AV block.

→ Can lead to Torsade’s de points

Hyperkalemia(see image 3)

Early ECG changes → Peaked T waves

→ Short PR interval

Later changes → Loss of P wave → followed widening of QRS complex → “sine wave” morphology.


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