Effect of Hypokalemia and Hyperkalemia on the Electrocardiogram

 2006-2007, Institute for Algorithmic Medicine, Houston, TX, USA.

Either a high (hyperkalemia) or a low (hypokalemia) serum potassium may be associated with significant changes in the electrocardiogram. There may be a poor correlation between the serum potassium levels and the ECG changes observed in the individual patient. Early recognition of changes in the ECG may allow early intervention before the onset of serious complications.




P wave

flattening, may disappear

increased amplitude and width

PR interval



QRS interval



ST segment


slight depression

T wave

increased amplitude and width

flattening or inversion

U wave


increased prominence

rate, rhythm

AV block, VF

premature beats; tachyarrhythmias, torsades de pointes

  • The P and T waves show opposite effects in hyperkalemia and hypokalemia.
  • Hypokalemia may enhance the tachyarrhythmias associated with digitalis toxicity.
  • Hyperkalemia may reduce the myocardial response to an artificial pacemaker.


Wagner GS. Marriott's Practical Electrocardiography, Ninth Edition. Williams & Wilkins. 1994. pages 180-183.